Deep Time: The Big Bang to Civilization
Events · 110
- 13.8 billion years agoBig Bang to Now
The Big Bang
About 13.8 billion years ago, the universe began in an extraordinarily hot, dense state and started to expand, and it has been expanding ever since. In the first tiny fraction of a second it went through a burst of runaway growth that cosmologists call cosmic inflation, during which space itself stretched faster than the speed of light. As it expanded it cooled, and over the following minutes the first atomic nuclei formed out of the cooling soup of particles. Every atom in your body, every star you can see, and every event further along this timeline traces back to this single beginning. NASA notes that the origin, evolution, and nature of the universe are still being worked out, so parts of the earliest instants remain open questions.
Reputable source · 3 sources - In the universe's first three minutesThe Early Universe
Big Bang Nucleosynthesis: the first elements
In the first seconds after the Big Bang, the universe was a hot, dense soup of protons, neutrons, electrons, and photons, far too hot for atomic nuclei to survive. As it expanded and cooled below about 1.2 billion degrees Kelvin, at an age of roughly 2 minutes, protons and neutrons began fusing into deuterium, an isotope of hydrogen. Within another minute, as the temperature dropped further, most of that deuterium fused into helium, with only trace amounts going on to form lithium. The whole process, physicists call it Big Bang nucleosynthesis, was over within about twenty minutes, once the universe had cooled and thinned out too much for further fusion. It left behind a universe that was roughly 75 percent hydrogen and 25 percent helium by mass, with only faint traces of anything heavier.
Reputable source · 2 sources - About 380,000 years after the Big BangThe Early Universe
Recombination and the discovery of the universe's oldest light
For its first 380,000 years, the universe was hot and dense enough that electrons roamed free, scattering light in every direction and keeping the whole cosmos opaque, like the inside of a cloud. As it cooled below about 3,000 kelvin, those electrons finally bound to nuclei to form neutral atoms, an event cosmologists call recombination. Light was suddenly free to travel in straight lines, and that exact burst of light is still arriving today, stretched by thirteen billion years of cosmic expansion into faint microwaves. It was found almost by accident in 1964, when Bell Labs radio astronomers Arno Penzias and Robert Wilson kept picking up a faint, uniform hiss their antenna could not explain. NASA's COBE satellite, launched in 1989, proved this cosmic microwave background had the precise blackbody spectrum an origin in a hot early universe predicts, and then found the faint temperature ripples, only parts per million, that mark the seeds of every galaxy that would ever form.
Reputable source - About 380,000 years after the Big BangBig Bang to Now
The first light: the cosmic microwave background
For its first few hundred thousand years the universe was so hot and crowded that a vast number of free electrons scattered light in every direction, leaving it in a kind of glowing fog through which nothing could be seen. Around 380,000 years after the Big Bang, in a stage scientists call recombination, it finally cooled enough for those electrons to join with nuclei into neutral atoms. Light was suddenly free to travel in straight lines, and it streamed out across the whole sky at once. That ancient light is still arriving today, stretched by the expanding universe into faint microwaves called the cosmic microwave background, the oldest light we can observe.
Primary source · 3 sources - About 13.7 billion years agoThe Early Universe
The cosmic dark ages: a universe with no stars at all
After recombination's burst of light faded, the universe went dark again, and stayed that way for roughly the next 200 million years. There were no stars yet, and no galaxies to hold them, only a thinning sea of neutral hydrogen and helium gas drifting through space under gravity's slow pull. NASA's account of this stretch, called the cosmic dark ages, describes gravity gradually pulling the densest knots of that gas closer together, patiently building the raw material that would eventually collapse into the first stars. It is, by definition, the one era in cosmic history with no light of its own to observe directly.
Reputable source - About 13.5 billion years agoBig Bang to Now
The first stars ignite
After the first light faded, the universe entered a long stretch astronomers call the dark ages, with no stars in it at all, only cooling clouds of hydrogen and helium left over from the Big Bang. Slowly, gravity drew those clouds together until the densest knots grew hot enough at their cores to ignite as the first stars. NASA describes these first stars as giants, 30 to 300 times the mass of our Sun and millions of times brighter, which meant they burned through their fuel quickly and died young in enormous explosions.
Reputable source · 2 sources - About 13.5 billion years agoThe Early Universe
The first stars ignite: giants with no metal in them at all
Deep inside the densest knots of the dark ages' hydrogen and helium clouds, gravity eventually packed enough gas together to ignite nuclear fusion, lighting the universe's first stars. NASA's account of these Population III stars describes them as almost certainly far more massive than the Sun and made of nothing but hydrogen and helium, since no heavier elements existed yet anywhere in the universe to mix into them. That missing chemistry mattered: with no metals to help gas cool efficiently while collapsing, these stars are thought to have grown enormous, burned through their fuel in a few million years, and died in violent supernovae that forged and scattered the universe's first heavier elements.
Reputable source - About 330 million years after the Big BangThe Early Universe
A galaxy that shouldn't exist yet: JWST's earliest surprise
In 2025 the James Webb Space Telescope observed a galaxy, catalogued JADES-GS-z13-1, as it appeared just 330 million years after the Big Bang. By every existing model of how reionization spread, a galaxy this young should still have been wrapped in the thick fog of neutral hydrogen that filled the early universe, fog that blocks exactly the kind of light this galaxy was showing off: a sharp, telltale glow called Lyman-alpha emission. Astronomer George Rieke's team found it anyway, clear and unmistakable, meaning the space around this one galaxy had already been cleared of its surrounding fog hundreds of millions of years before reionization was thought to finish everywhere else. 'We really shouldn't have found a galaxy like this,' one team member said, 'given our understanding of the way the universe has evolved.'
Reputable source - About 13 billion years agoBig Bang to Now
The Milky Way begins to form
Our own galaxy started coming together remarkably early. Using data from its Gaia mission, which measured the positions, motions, and ages of millions of individual stars, the European Space Agency showed that a major part of the Milky Way known as the thick disc began forming about 13 billion years ago. That is only around 0.8 billion years after the Big Bang, and roughly 2 billion years earlier than astronomers had expected the galaxy's structure to appear.
Peer-reviewed · 2 sources - By about 12.8 billion years ago (the universe's first billion years)The Early Universe
Reionization: starlight burns away the cosmic fog
As more and more of the first stars and galaxies switched on, their ultraviolet light did more than just illuminate the universe, it began tearing electrons back off the neutral hydrogen atoms that had formed at recombination, ionizing the gas that filled all of space. NASA's account of this epoch of reionization describes the ultraviolet light from those young stars breaking down hydrogen atoms into free electrons and protons, spreading in expanding bubbles around each new source of starlight. Over several hundred million years those bubbles grew and merged, and by the time the universe was about a billion years old, essentially all of that primordial hydrogen fog had been cleared.
Reputable source - About 10 billion years agoThe Early Universe
The Milky Way's violent youth: the galaxy we swallowed
About 10 billion years ago, roughly 3 billion years after the Milky Way's thick disc had already begun forming, our galaxy collided with another galaxy roughly a quarter its size, comparable to one of the Magellanic Clouds still visible in the night sky today. The European Space Agency's Gaia satellite uncovered the wreckage by mapping the positions and motions of roughly 30,000 stars that move on elongated orbits running backward against the rest of the galaxy's hundred billion stars, a signature no ordinary formation process produces. Astronomers named the vanished galaxy Gaia-Enceladus. Its stripped-apart stars now make up most of the Milky Way's inner halo, and its debris carried with it hundreds of variable stars and thirteen globular clusters that still trace the same telltale backward orbits.
Reputable source - About 4.6 billion years agoThe Formation of the Solar System
A collapsing cloud of gas and dust starts to spin
The Solar System started as a cold, slowly turning cloud of gas and dust, mostly hydrogen and helium left from the Big Bang, salted with heavier elements that earlier stars had forged and scattered when they died. NASA's account has the collapse begin when the shockwave from a nearby exploding star, a supernova, swept through a denser pocket of the cloud and set it contracting under its own gravity. As the cloud fell inward it spun faster and flattened, the way a skater speeds up by pulling in their arms, until almost all of the material had piled into a hot, dense center. That center became the young Sun.
Reputable source - 4.6 billion years agoBig Bang to Now
The Sun and Solar System form
About 4.6 billion years ago, a giant, slowly spinning cloud of gas and dust called the solar nebula began to collapse under its own gravity. Most of the material fell inward and piled up at the center until it grew dense and hot enough to ignite as the Sun, which NASA describes as a yellow dwarf star, a hot glowing ball of hydrogen and helium about 4.5 billion years old. The leftover material spread into a disk around the new star, and out of that disk the planets, moons, asteroids, and comets slowly assembled.
Peer-reviewed · 2 sources - About 4.567 billion years agoThe Formation of the Solar System
The oldest solids we can date: 4.567 billion years
Scattered through the oldest meteorites are pale specks a few millimetres across called calcium-aluminium-rich inclusions, or CAIs. They were the first solid material to condense from the hot inner disk, and they are the oldest objects anyone has dated: lead-lead radiometric dating puts them at about 4,567 million years, with an uncertainty of only tens of thousands of years. Because they formed right at the start, that number defines the age of the Solar System itself. Work at Lawrence Livermore on these grains found the disk's first solids came together in under roughly 200,000 years, a geological eyeblink.
Reputable source · 2 sources - About 4.56 billion years agoThe Formation of the Solar System
The giant planets take shape and carve the asteroid belt
Beyond the frost line, where ice joined rock and metal as building material, Jupiter and Saturn grew far faster and larger than the inner worlds and drew in thick envelopes of gas to become the giant planets. Their gravity then reshaped everything closer in. NASA credits the young Jupiter's pull with ending planet formation in the gap between Mars and Jupiter, stirring the bodies there so hard that they shattered in collisions instead of merging, and that stranded rubble is the asteroid belt. A 2023 study in Scientific Reports models how a near-resonant Jupiter and Saturn set off chaotic gravitational stirring that emptied the disk beyond about 1 to 1.5 times the Earth-Sun distance over some 5 to 10 million years.
Peer-reviewed · 2 sources - About 4.55 billion years agoThe Formation of the Solar System
Dust to planets: accretion builds the worlds
Inside the disk, grains of dust collided and stuck, and the clumps that grew biggest pulled in more material with their stronger gravity. This runaway sticking, called accretion, built pebbles into boulders, boulders into kilometre-wide planetesimals, and planetesimals into Mars-sized planetary embryos. Close to the Sun the disk was too hot for ice or gas to survive, so only rock and metal could condense; that inner zone produced the small rocky planets Mercury, Venus, Earth, and Mars. Past the frost line, where it was cold enough for ice and gas to pile onto growing cores, the giant planets Jupiter and Saturn took shape.
Reputable source - About 4.54 billion years agoThe Formation of the Solar System
Earth reaches its full size, 4.54 billion years ago
Earth grew to nearly its present mass by sweeping up rock and metal from its zone of the disk over tens of millions of years. The planet's age is pinned to about 4.54 billion years, and the figure comes not from any Earth rock but from meteorites, leftover building material that was never reworked. Lead-isotope dating of the Canyon Diablo iron meteorite, treated as part of the same system as the Earth, gives an age for the Earth and meteorites of 4.54 billion years, with an uncertainty under one percent.
Reputable source - About 4.5 billion years agoBig Bang to Now
Earth forms
As the young Solar System settled into its current layout about 4.5 billion years ago, gravity pulled swirling gas and dust in the disk around the Sun together into larger and larger clumps, and one of them became Earth, the third planet out. The early Earth was a violent, largely molten world, bombarded by leftover debris and far too hot for the oceans and continents we know. Over time it cooled, grew a solid crust, released gases that formed an early atmosphere, and eventually held liquid water.
Reputable source · 2 sources - About 4.5 billion years agoBig Bang to Now
The giant impact that made the Moon
Not long after Earth formed, it suffered one of the most violent events in its history. The leading explanation, the giant impact theory, holds that an object roughly the size of Mars struck the young Earth and flung enough molten and vaporized rock into space that the debris settled into orbit and came together to form the Moon. NASA places this collision near the time of the Solar System's formation, about 4.5 billion years ago, and notes that any complete theory of the Moon still has to explain everything we observe about it today.
Peer-reviewed · 2 sources - About 4.5 billion years agoThe Formation of the Solar System
The giant impact that made the Moon
Within the first hundred million years after Earth formed, a world about the size of Mars struck the young planet a glancing blow. NASA calls this the giant-impact hypothesis and names the impactor Theia. The collision melted much of the Earth and flung a huge quantity of vaporized rock into orbit, where it gathered into the Moon. The theory accounts for features that are otherwise hard to explain: the Moon's small iron core, signs that it was once molten to great depth, and the near-identical oxygen-isotope makeup of lunar and terrestrial rock, as if both were cut from the same material.
Peer-reviewed · 2 sources - About 4.5 billion years agoThe Formation of the Solar System
Earth settles into a layered core and a magnetic shield
Heated by its own accretion and by the giant impact, the young Earth settled into the layers it still has: a solid inner core and a molten outer core of iron and nickel, a thick rocky mantle, and a thin crust. NASA puts the solid inner core at about 1,220 kilometres in radius, wrapped in a liquid outer core roughly 2,300 kilometres thick. That churning liquid metal, driven by heat leaking out of the core and twisted by Earth's spin, runs as a geodynamo: it sets up electric currents that produce Earth's magnetic field, which reaches out into space as the magnetosphere.
Reputable source · 2 sources - About 4.4 billion years agoThe Formation of the Solar System
The oldest surviving piece of Earth: a 4.4-billion-year-old crystal
No rock survives from Earth's first few hundred million years, but a single mineral does. In the Jack Hills of Western Australia, geologists recovered tiny zircon crystals, one dated to about 4,404 million years, that had weathered out of long-vanished rocks and been sealed into younger sandstone. Reported in Nature in 2001 by Simon Wilde and colleagues and studied by John Valley's group, the grains carry a chemical clue: an elevated ratio of oxygen-18 to oxygen-16, the signature a rock picks up when it has interacted with liquid water. Their message is that by 4.4 billion years ago Earth already had liquid water at its surface and a solid crust.
Peer-reviewed · 2 sources - By about 4.4 billion years agoThe Formation of the Solar System
Earth gets its oceans and first atmosphere
The Earth that emerged from its violent formation had no breathable air and no seas. Its first atmosphere and oceans came from two sources, according to NASA: gases and water vapour erupting from volcanoes across the young crust, and water carried in by the asteroids and comets still striking the planet, some of it as ice that melted on impact. As the surface cooled enough for that water vapour to condense, it fell as rain and gathered into the first oceans. The 4.4-billion-year-old zircons say liquid water was already present by then, so the seas formed early.
Reputable source · 2 sources - About 4.03 billion years agoThe Formation of the Solar System
The oldest intact rock on Earth: the Acasta Gneiss
The zircons are single crystals, but the oldest whole rock still in place is the Acasta Gneiss, exposed along the Acasta River in Canada's Northwest Territories. Uranium-lead dating of zircons inside it gives an age of about 4.03 billion years, which the Geological Survey of Canada records as the oldest known rock on Earth. It began as igneous rock and was later cooked and squeezed into the banded gneiss seen today, part of the ancient core of the North American continent.
Reputable source - Around 4 billion years ago (estimates span 2 to 4 billion)Early Life on Earth
LUCA and the chemistry of the first cells
Every living thing alive today, from bacteria to blue whales, traces back to a single ancestral microbe biologists call LUCA, the Last Universal Common Ancestor. NASA Astrobiology dates LUCA to around 4 billion years ago, though it notes the split into today's separate domains of life could have happened anywhere between 2 and 4 billion years ago. LUCA was not a simple ancestor waiting to be improved on. It already ran on molecular hydrogen as an energy source, building organic compounds out of hydrogen, carbon dioxide, and nitrogen, a chemistry that points to a home in alkaline hydrothermal vents, cracks in the seafloor rich in iron and sulfur where hot, mineral-laden water met cold ocean.
Reputable source - Around 4 to 3.9 billion years ago (disputed)The Formation of the Solar System
The Late Heavy Bombardment, and why it is disputed
Around 4 billion years ago the young Earth and Moon may have been hit by a spike of asteroid and comet impacts, an episode called the Late Heavy Bombardment. The idea came from Apollo Moon rocks: many impact-melted samples from different landing sites clustered near the same age of roughly 4 billion years, hinting at a single violent pulse. NASA is blunt that the idea 'was and remains fairly controversial.' Later work showed lunar basins are very hard to date and that the Apollo samples may all be contaminated by debris from one or two big impacts, so the apparent cluster could be an artifact of where the astronauts happened to land.
Peer-reviewed · 2 sources - About 3.8 billion years agoBig Bang to Now
Life begins on Earth
Sometime in Earth's first billion years, in the planet's early oceans, chemistry crossed the line into biology and the first living things appeared. NASA points to those vast early oceans as a convenient place for life to begin about 3.8 billion years ago. The earliest organisms were microscopic, single-celled, and left only faint chemical and fossil traces in very old rocks, which is why the exact timing is uncertain and the earliest claimed evidence is actively debated by scientists.
Peer-reviewed · 2 sources - About 3.48 billion years ago (a rival claim reaches 3.7 billion)Early Life on Earth
The oldest debated evidence of life
In the Dresser Formation of the Pilbara Craton in Western Australia, geologists have documented stromatolites, layered mounds built by microbial mats, dated to about 3.48 billion years old, alongside fossilized hot-spring mineral deposits called geyserite. A study in Nature Communications treats this combination, stromatolites plus fractionated carbon and sulfur isotopes plus the geyserite itself, as some of Earth's earliest convincing evidence of life, and the first sign that early life lived on land in hot springs, not only in the sea. A rival, older claim goes further: in 2016 a team led by Allen Nutman reported what they called microbial structures in 3.7-billion-year-old rock at Isua, Greenland, in Nature. Other geologists pushed back hard. Abigail Allwood's team re-examined the Isua structures and argued they were lined up too neatly, like children's toes in a row, and lacked the internal layering real stromatolites should have, favoring a non-biological origin from rock deformation instead.
Peer-reviewed · 3 sources - About 2.4 billion years agoBig Bang to Now
The Great Oxidation Event
For roughly the first half of Earth's history the air held almost no free oxygen, and the planet's chemistry was completely different from today's. Then cyanobacteria, microbes that make energy from sunlight through photosynthesis, released oxygen as a waste product, and over hundreds of millions of years it built up faster than the rocks and oceans could absorb it. The American Society for Microbiology places this Great Oxidation Event sometime between about 2.4 and 2.1 billion years ago, when oxygen finally accumulated in the atmosphere.
Peer-reviewed · 2 sources - About 2.5 to 2.3 billion years agoEarly Life on Earth
The Great Oxidation Event
For well over a billion years, life on Earth ran without free oxygen. That changed when cyanobacteria mastered oxygenic photosynthesis, splitting water molecules with sunlight and releasing oxygen as a byproduct. NASA Astrobiology dates the resulting Great Oxidation Event to between 2.5 and 2.3 billion years ago, the point when oxygen first accumulated in Earth's atmosphere and has stayed present ever since. It was not instant. Newly released oxygen reacted with dissolved iron in the oceans first, rusting out of seawater as it went, before enough built up to escape into the air. NASA-funded research on ancient stromatolites in Australia's Shark Bay also found signs of oxygen in small pockets of shallow ocean water even before the main event, a more gradual warm-up than a single global switch flipping.
Reputable source · 2 sources - By about 2.1 billion years agoEarly Life on Earth
Eukaryotes appear: a cell swallows a cell
The simple bacteria and archaea that had run life for two billion years shared one limitation: no internal compartments, no nucleus, no organelles. That changed with the eukaryotes, cells built from the inside out through endosymbiosis, in which a host cell engulfed a free-living bacterium instead of digesting it and kept it on as a permanent, useful resident. Biologist Lynn Margulis argued in 1967 that mitochondria, chloroplasts, and even the whip-like flagella eukaryotic cells use to swim were each once independent bacteria, a claim rejected by journal after journal before it was finally published and eventually became the accepted explanation. The oldest strong fossil evidence for this new kind of cell is Grypania spiralis, a spiral-coiled, thread-like organism up to half a metre long, found in the 2.1-billion-year-old Negaunee Iron Formation near Marquette, Michigan.
Peer-reviewed · 2 sources - About 1.8 to 0.8 billion years agoEarly Life on Earth
The Boring Billion: life idles for a billion years
For roughly a billion years, geologically and biologically, almost nothing appeared to happen. Continents drifted with unusual stability, the climate held remarkably steady, and complex life barely diversified, a stretch of time paleontologists nicknamed the Boring Billion. The likely brake was oxygen: research summarized in a Scientific Reports study puts atmospheric and oceanic oxygen during this period at well under 1% of today's level, with the deep ocean widely oxygen-poor and often sulfidic, chemistry hostile to the animals that would eventually need real quantities of oxygen to grow large and active.
Peer-reviewed - 1.047 billion years agoEarly Life on Earth
Bangiomorpha: the first sex, the first true multicellular life
In rocks first collected on Baffin and Somerset Islands in Arctic Canada, paleontologist Nicholas Butterfield described a fossil red alga, Bangiomorpha pubescens, built from differentiated filaments of cells rather than a single cell alone, some specialized for spores and others for reproduction. A 2018 re-dating using rhenium-osmium radiometric methods pinned the fossil to 1.047 billion years old, about 150 million years younger than earlier estimates, and McGill University, whose researchers led that dating work, calls Bangiomorpha the oldest known direct ancestor of modern plants and animals. Butterfield's original description argued the fossil's cell differentiation is best explained as evidence of sexual reproduction, the oldest such evidence on record, arising alongside true multicellularity rather than after it.
Reputable source · 2 sources - About 890 million years ago (disputed)Early Life on Earth
Possibly the first animals: a disputed sponge
In weathered reef rock in Canada's Northwest Territories, geologist Elizabeth Turner identified microscopic branching structures she interprets as the fossilized skeletal fibers of keratosan demosponges, a group of simple sponges alive today. Published in Nature in 2021, the claim would push the animal fossil record back to about 890 million years ago, roughly 350 million years earlier than the next-oldest confirmed animal fossils, with the sponges living as small patches tucked into the nooks of ancient microbial reefs. The claim has not been accepted. Paleobiologist Nicholas Butterfield, the same researcher who described Bangiomorpha, argued that several past claims of sponge fossils in similarly aged rock were later disproven, and that an animal turning up this early runs against the expectation that a genuinely new, successful body plan spreads and diversifies quickly rather than staying rare and easy to miss for hundreds of millions of years.
Peer-reviewed · 2 sources - About 720 to 635 million years agoEarly Life on Earth
Snowball Earth: the planet freezes over
Twice during the Cryogenian period, roughly 720 to 710 million years ago and again around 640 million years ago, geological evidence shows glaciers reaching all the way to the equator, each episode lasting on the order of 10 million years. NASA's Goddard Institute for Space Studies points to glacial deposits found at tropical latitudes as the core evidence: if ice reached the tropics on land, the logic runs, it likely wrapped the whole planet, a hypothesis known as Snowball Earth. The most recent of these glaciations ended around 635 million years ago, just as complex life was beginning to take shape. How it ended is genuinely unresolved. The standard explanation holds that volcanic carbon dioxide slowly built up beneath the ice until it thawed the planet, but NASA's own researchers note there is no geologic evidence for atmospheric carbon dioxide ever reaching the level that explanation requires, which has pushed some scientists toward a milder 'Slushball Earth' with open water at the equator instead of a solid ice shell.
Peer-reviewed · 2 sources - About 574 to 539 million years agoEarly Life on Earth
The Ediacaran biota: animals fill the world
In the last tens of millions of years before the Cambrian, the fossil record fills with strange, soft-bodied organisms unlike anything alive today, first found in 1946 at the Ediacara Hills in South Australia and since recovered on every continent except Antarctica. NASA Astrobiology's account of the Nilpena fossil site in South Australia calls this the first time animals moved through open water, the first time they crawled or grazed the seafloor, and the first time some of them reproduced sexually. The best-known member, Dickinsonia, was a flattened, ribbed oval that could grow over a metre across. For decades its identity was debated: animal, fungus, giant single-celled organism, no one could say for certain. That changed when researchers led by Jochen Brocks analyzed molecules preserved in a Dickinsonia fossil from Russia's White Sea coast and found it held up to 93 percent cholesterol, a molecule that regulates animal cell membranes, while the sediment around the fossil held a completely different molecule associated with algae and fungi. Brocks described the contrast as black and white.
Reputable source · 2 sources - About 541 to 521 million years agoThe Cambrian Explosion
Small shells and spines: the first mineralized skeletons
In the roughly 20 million years between the start of the Cambrian and the appearance of trilobites, the fossil record fills with tiny, hard fragments known collectively as the small shelly fauna: spines, tubes, armor plates, and shells a millimetre or two across, built from apatite, the same calcium phosphate mineral as bone and teeth, or from calcium carbonate like a modern snail's shell. They represent some of the first evidence that animals had begun building mineral skeletons at all. Some belong to early molluscs, brachiopods, and other recognizable lineages; many others remain what paleontologists frankly label 'problematica,' fragments whose parent animal nobody has yet identified.
Reputable source - About 539 million years agoBig Bang to Now
The Cambrian explosion
The Cambrian Period, which the Natural History Museum dates from about 539 to 485 million years ago, opened with a burst of animal evolution so rapid and far-reaching that it is called the Cambrian explosion. In a geologically short window, thought to be only the first 20 million years or so of the period, animals diversified into full-bodied creatures with a wide range of body plans and lifestyles. Those body plans define what scientists call phyla, the major groups all animals are sorted into, of which there are nearly 40. Trilobites, hard-shelled arthropods with jointed legs and antennae, are the characteristic animals of the period.
Peer-reviewed · 2 sources - 538.8 million years agoThe Cambrian Explosion
The Cambrian explosion begins
The Cambrian Period opened about 538.8 million years ago, and within a geologically short window, perhaps only its first 20 million years, animal life diversified into nearly every major body plan alive today. The Natural History Museum dates the period from 539 to 485 million years ago and credits this opening burst with producing the body plans that define almost 40 animal phyla, the broadest categories life is sorted into. Before this, the Ediacaran world held soft-bodied, largely immobile organisms. After it, oceans held fast-moving predators, armored prey, and burrowing scavengers, the entire architecture of animal life compressed into a sliver of geological time.
Reputable source - About 535 million years ago (the cause is still debated)The Cambrian Explosion
Why so fast? The unresolved cause of the explosion
No single explanation for the speed of the Cambrian explosion has won out. The Royal Ontario Museum's own account of the debate lays out the leading, competing hypotheses. A rise in atmospheric and ocean oxygen could have allowed larger, more active animals to exist, though oxygen levels show little clear change right at the Ediacaran-Cambrian boundary. Small shifts in Hox genes, the master switches that lay out an animal's body plan during development, could have unlocked a much larger range of possible body shapes from only minor genetic changes. Predation itself may have driven the burst: once some animals began hunting others, the hunted evolved shells and burrowing to escape, and the hunters evolved better senses and weapons in response, an evolutionary feedback loop with no obvious stopping point. Zoologist Andrew Parker has argued more specifically that the sudden evolution of camera-like vision was the trigger, since sight let predators hunt at a distance for the first time, but other researchers, including Martin Brasier, counter that sharp eyes appear too late in the sequence to have started it.
Reputable source · 2 sources - About 521 million years ago onwardThe Cambrian Explosion
Trilobites: eyes built from stone
Trilobites, hard-shelled arthropods with jointed legs and antennae, appeared around 521 million years ago and quickly became one of the dominant animal groups of the Cambrian and early Ordovician oceans. Their most distinctive feature was their eyes, built from stacked prisms of calcite, the same mineral as limestone and chalk, each prism angled slightly differently from its neighbors to build a compound image. The Natural History Museum notes this is a feature no other animal, before or since, is known to have evolved: every other compound eye in nature is built from soft or organic lens material, never solid mineral crystal.
Reputable source - About 538 to 500 million years agoThe Cambrian Explosion
The Cambrian substrate revolution: animals rebuild the seafloor
Before the Cambrian, the seafloor was carpeted in tough microbial mats, and burrowing animals barely disturbed it, leaving a firm, sealed surface with almost no mixing between the top layer of sediment and the water above. A 2000 paper in GSA Today by David Bottjer, James Hagadorn, and Stephen Dornbos, drawing on years of prior fieldwork, documents how Cambrian animals overturned this arrangement: as burrowing organisms increasingly churned sediment vertically, not just sideways, the old mat-sealed seafloor gave way to a soft, waterlogged, mixed layer, the loose muddy seabed still typical of shallow oceans today. The paper traces this substrate revolution's direct evolutionary toll on two groups of stalked, filter-feeding echinoderms: small sediment-perching helicoplacoids, which depended on the old firm seafloor and went extinct as it disappeared, while edrioasteroids and eocrinoids survived the same change by evolving root-like holdfasts and stems to anchor onto hard surfaces instead.
Peer-reviewed - About 518 million years agoThe Cambrian Explosion
Haikouichthys: the first fish, the first vertebrates
Among the Chengjiang biota's fossils is Haikouichthys, a slender, two-and-a-half-centimetre animal that the Natural History Museum lists among the earliest vertebrates in the fossil record. Its impression shows a notochord, the flexible internal supporting rod that is a hallmark of all chordates, along with what appear to be traces of a skull and vertebral elements, features that put it on the vertebrate branch of the family tree rather than merely near it. It shared its Chengjiang world with the earlier-discovered, less fish-like Pikaia, but Haikouichthys and its close relative Myllokunmingia, both from Chengjiang, show more developed vertebrate anatomy and are considered closer to the actual root of the vertebrate lineage.
Reputable source - About 518 million years agoThe Cambrian Explosion
China's rival windows: Qingjiang and Chengjiang
The Burgess Shale is not alone. In southern China, a cluster of similarly exceptional fossil beds preserves an even earlier slice of the Cambrian explosion, roughly 518 million years old, about 10 million years older than the Burgess Shale itself. The Chengjiang biota, discovered in Yunnan Province in 1984, was the first of these Chinese windows recognized, and it remains one of the richest, documenting at least sixteen animal phyla. More recently, the Qingjiang biota, described from Hubei Province and reported in Science in 2019, turned up so many previously unknown species, over half its species were new to science, that researchers described it as rivaling both the Burgess Shale and Chengjiang for both preservation quality and diversity.
Reputable source · 2 sources - Fossils about 508 million years old, discovered in 1909The Cambrian Explosion
Charles Walcott finds the Burgess Shale
On August 30, 1909, Smithsonian administrator and geologist Charles Walcott, riding the high slopes of the Canadian Rockies near what is now Yoho National Park, spotted a loose slab of shale containing fossils unlike anything he had cataloged before. He returned the following year with his family and worked the resulting quarry almost every summer until 1924, eventually extracting some 60,000 specimens now held at the Smithsonian Institution. What made the site extraordinary was not just its age of roughly 508 million years, but its preservation: soft body parts, gills, guts, and delicate limbs that almost never survive fossilization were flattened and preserved as carbon films, revealing animals whose entire soft anatomy would otherwise have vanished without a trace.
Reputable source - About 506 million years agoThe Cambrian Explosion
Anomalocaris: the apex predator that was mistaken for three animals
At up to a metre long, Anomalocaris was the largest hunter of the Cambrian seas, a swimming predator with grasping spiked appendages and a circular, tooth-lined mouth. For nearly a century it was not recognized as one animal at all. In 1892, Joseph Whiteaves described its grasping arms as the tail of a separate shrimp-like creature; Charles Walcott, working the Burgess Shale, identified its mouth as a jellyfish he named Peytoia; and Simon Conway Morris mistook its body for a sponge he called Laggania. Only in 1985 did Harry Whittington and Derek Briggs recognize that all three fossils were fragments of the same single animal. In 2011, a study in Nature examining fossilized eyes from an Australian Anomalocaris relative found each eye held at least 16,700 individual lenses, rivaling the resolution of a modern dragonfly's eye.
Peer-reviewed · 2 sources - About 470 million years agoLife Conquers the Land
Plants leave the water for good
Rock from the Ordovician Period carries the first evidence that plants had begun colonizing dry land, in the form of microscopic spores called cryptospores, distinct from anything a marine alga produces. The U.S. National Park Service notes that the first unquestioned plant fossils come slightly later, from the Late Silurian, but the earlier Ordovician spore evidence points to the same slow migration: plant ancestors most likely evolved first in the sea, moved into fresh water, and only then, gradually, onto land itself.
Reputable source - About 430 million years agoLife Conquers the Land
The first jaws: placoderms take a bite out of the world
The oldest known placoderms, an armored, extinct group of fish, appear in the fossil record from the late Early Silurian in China, and they carried something no vertebrate before them had: a jaw. The University of California Museum of Paleontology places placoderms as the earliest branch of the gnathostomes, the jawed vertebrates that include every fish, amphibian, reptile, bird, and mammal alive since. Odd as it sounds, placoderms never evolved teeth. Bony plates built into the jaw itself did a tooth's job instead, some wearing into naturally self-sharpening edges as the animal fed.
Reputable source - About 380 to 360 million years agoLife Conquers the Land
Dunkleosteus: the strongest bite in the Devonian seas
By the late Devonian, the placoderm lineage had produced Dunkleosteus, an armored predator that grew to an estimated 6 metres and 1,000 kilograms and became one of the first vertebrate apex predators in any ecosystem on Earth. A 2006 biomechanical study modeled its skull and found a bite force of over 4,400 newtons at the jaw tip and more than 5,300 newtons at the rear of its bladed dental plates, concentrating enough stress at the cutting edge, over 100 million newtons per square metre, to puncture and fragment armor plating as tough as its own. Rather than teeth, Dunkleosteus's mouth was lined with sharpened bony blades that could shear through the armored placoderms and other fish sharing its ocean.
Peer-reviewed - About 375 million years ago (found in 2004)Life Conquers the Land
Tiktaalik: the fish that was becoming something else
In 1998, paleontologist Neil Shubin was flipping through an undergraduate geology textbook when he noticed a map of Devonian-age rock outcrops, one of them in the Canadian Arctic, largely unexplored. After finding an old paper comparing that site's geology to formations he already knew, Shubin's team spent several difficult field seasons searching Ellesmere Island for fossils of exactly the age they needed, at the edge of their funding, before finally finding what they were looking for in 2004: Tiktaalik roseae, a nine-foot fish with a flat, crocodile-like skull, gills, and, on top of its head, air-breathing nostrils called spiracles. Its fins carried fish-like rays for paddling, but inside them sat sturdy bones corresponding to an upper arm, forearm, and even a wrist, along with a hip and pelvis built sturdier than a fish preparing to swim should need.
Reputable source · 2 sources - About 365 million years agoLife Conquers the Land
Ichthyostega and Acanthostega: the first four legs on land
In rock from what is now Greenland, paleontologists have found Ichthyostega and Acanthostega, two of the earliest true tetrapods, four-limbed vertebrates with digits rather than fins. Acanthostega was long treated as the more primitive of the two, the first vertebrate with fingered limbs, while Ichthyostega combined a still fish-like, finned tail and a fish-like skull with weight-bearing limb bones and a reinforced ribcage built to support a body out of water. More recent analysis has complicated that tidy story: Ichthyostega's pelvis and vertebrae now look more built for land than Acanthostega's, hinting that Acanthostega, despite its early reputation, may actually have spent much of its life back in the water.
Reputable source - About 320 to 300 million years agoLife Conquers the Land
The Carboniferous coal forests: giant bugs in super-oxygenated air
Vast swampy forests spread across the land in the Carboniferous Period, and because wood-decomposing fungi had not yet evolved to break it down efficiently, dead plant matter piled up and was buried rather than rotting and releasing its carbon back into the air, the same buried plant matter that would later become coal. That buildup pushed atmospheric oxygen to levels estimated as high as 35 percent, far above today's 21 percent. A peer-reviewed study on insect body size found that oxygen this abundant let arthropods sidestep a physical limit: insects breathe through narrow tubes called tracheae that ordinarily choke off oxygen supply to a large body, so with oxygen this plentiful, gigantism became viable. The result included Meganeura, a dragonfly relative with a wingspan up to 75 centimetres, and Arthropleura, a millipede that grew past 2 metres, the largest land arthropod ever known.
Peer-reviewed - About 312 million years agoLife Conquers the Land
Hylonomus and the egg that freed vertebrates from the water
Near Joggins, Nova Scotia, fossil hunters found the remains of Hylonomus lyelli sealed inside the hollow, rotted-out stumps of fossilized club-moss trees, a small, 20-to-25-centimetre lizard-like animal that had likely crawled in seeking shelter and become trapped. Hylonomus is considered the earliest known reptile, and, more specifically, the earliest known amniote, the group whose eggs carry their own protective membrane and no longer need to be laid in water. That single innovation, a self-contained egg an animal could lay on dry land, is what let its descendants push inland, away from the rivers, swamps, and coasts every vertebrate before them had stayed tied to.
Reputable source · 2 sources - About 252 million years agoAge of Dinosaurs
The Great Dying clears the stage
The Mesozoic Era, the age of dinosaurs, began in the aftermath of catastrophe. About 252 million years ago the Permian-Triassic extinction, which the Natural History Museum calls the Great Dying, wiped out more than 95 percent of all species and stands as the largest mass extinction in Earth's history. On land and in the seas, most life was eradicated. The exact trigger is still argued over, with huge volcanic eruptions in what is now Siberia among the leading suspects, and by some estimates the planet took millions of years to recover.
Peer-reviewed · 3 sources - From about 250 million years agoAge of Dinosaurs
Sea dragons take the oceans
As life recovered from the Great Dying, reptiles moved back into the sea. Among the first were the ichthyosaurs, marine reptiles the Natural History Museum calls the real sea dragons, whose oldest fossils date from right at the end of the Permian into the Early Triassic, around 250 million years ago. Over time some grew to enormous size, while others took on streamlined shapes that made them look strikingly like today's dolphins as they dashed through the water. They were reptiles, not fish and not dinosaurs, breathing air while living their whole lives at sea.
Peer-reviewed · 2 sources - About 245 million years agoBig Bang to Now
Dinosaurs rise
Dinosaurs first appeared in the Triassic Period, around 245 million years ago, and went on to dominate life on land for the next 180 million years or so, through the Jurassic and Cretaceous that followed. Over that immense span they ranged from small, fast, feathered hunters to the largest animals ever to walk the Earth. One branch of the dinosaurs survived everything that came later and is still alive all around us: the birds.
Peer-reviewed · 2 sources - About 240 million years agoAge of Dinosaurs
The first dinosaurs appear
The Natural History Museum places the first dinosaurs in the fossil record around 240 million years ago, during the Triassic Period, which ran from 252 to 201 million years ago. These earliest dinosaurs were small, bipedal creatures, a modest start for a group that would go on to include the largest animals ever to walk the Earth. They shared the Triassic world with many other kinds of reptile and were not yet dominant.
Peer-reviewed · 3 sources - About 215 to 66 million years ago (Late Triassic to end of the Cretaceous)Age of Dinosaurs
Pterosaurs rule the air
Pterosaurs first turn up in the fossil record around 215 million years ago in the Late Triassic and lasted until the same asteroid impact that ended the Cretaceous, 66 million years ago. The Natural History Museum is direct about a common misconception: pterosaurs were not dinosaurs, but their own separate branch of reptile, related to dinosaurs only in that both descend from a shared archosaur ancestor further back in time before the two lines split. Their wings were not feathered but built from a thin skin membrane, stretched from an elongated finger to the ankle and reinforced with internal fibres rather than a skeleton of multiple wing fingers. The largest of them, Quetzalcoatlus, had a wingspan of roughly 11 metres, about the size of a small airplane, stood some 2.5 metres tall at the shoulder, roughly the height of a giraffe, yet weighed only up to about 250 kilograms.
Peer-reviewed · 2 sources - About 201 million years ago (the Triassic-Jurassic boundary)Age of Dinosaurs
The end-Triassic extinction opens the world to dinosaurs
At the end of the Triassic, about 201 million years ago, a mass extinction swept away many of the large land animals that had shared the world with the first dinosaurs, including groups like phytosaurs, aetosaurs, and other reptile relatives that had until then rivaled or outnumbered them. The U.S. National Park Service names massive volcanic eruptions, tied to the beginning of Pangaea's breakup, as the most likely primary cause, releasing gases that disrupted the climate and ocean chemistry. Both the National Park Service and the Natural History Museum are direct about the limits of that certainty: the Natural History Museum states the causes of this extinction are still hotly debated among scientists.
Reputable source · 3 sources - From about 201 million years ago (end of the Triassic) onwardAge of Dinosaurs
Pangaea breaks apart beneath the dinosaurs' feet
When dinosaurs first appeared, all of Earth's land was joined into a single supercontinent, Pangaea. Toward the end of the Triassic, around 201 million years ago, huge volcanic eruptions began tearing it apart along the boundary between what is now North America and Africa, opening the earliest North Atlantic Ocean. During the Jurassic that followed, Pangaea split fully into two: Laurasia in the north and Gondwana in the south. The Natural History Museum notes that fossil records still show similarities between the two halves early in the Jurassic, meaning some land connections lingered, but the two landmasses grew more distinct as the period went on. By the Cretaceous, the pieces had separated further into something close to today's continents, still adrift from their modern positions. The U.S. Geological Survey frames the whole process as spanning nearly the full 165-million-year run of the dinosaurs.
Reputable source · 3 sources - Late Jurassic, about 149 to 145 million years agoAge of Dinosaurs
Archaeopteryx: feathers between dinosaurs and birds
In the Late Jurassic, around 149 to 145 million years ago, a small, bird-like dinosaur called Archaeopteryx lived in what is now Germany. About the size of a magpie, it had broad feathered wings and could fly, yet it kept features no modern bird has, including sharp teeth and a long bony tail. The Natural History Museum bought the first skeleton in 1862, now called the London specimen and displayed in its Cadogan gallery, and it became one of the most famous fossils in the world.
Peer-reviewed · 3 sources - Late Jurassic, about 152 to 145 million years agoAge of Dinosaurs
Allosaurus hunts the giants
Allosaurus was a large, two-legged predator that hunted across what is now the United States in the Late Jurassic, about 152 to 145 million years ago, growing to roughly 9.7 metres long and 2,700 kilograms, armed with dagger-like, serrated teeth, three-fingered hands, and small horns above its eyes. The Natural History Museum reports direct fossil evidence of its diet: Stegosaurus fossils bearing Allosaurus bite marks, and separate evidence that it scavenged the remains of large sauropods, though experts are not certain whether it regularly killed such enormous prey alive or fed on carcasses it found already dead. Multiple Allosaurus skeletons have also turned up together in the same bone beds, which has led some researchers to wonder whether the species hunted in packs, a hypothesis the museum treats as unresolved rather than settled.
Reputable source · 2 sources - Late Jurassic, about 152 to 145 million years agoAge of Dinosaurs
Stegosaurus and the mystery of the plates
Stegosaurus lived in what is now the United States in the Late Jurassic, about 152 to 145 million years ago, growing to roughly 9 metres long, defended by a powerful spiked tail it could swing at predators such as Allosaurus. Its signature row of bony plates was embedded in its skin rather than fused to its skeleton, which is why fossil plates are usually found separated from the body. The Natural History Museum states plainly that scientists are not certain what the plates were for: possibilities include warning off predators, helping members of the species recognize each other, or regulating body temperature, an idea supported by tiny grooves in the plate surfaces that may have held blood vessels. When the paleontologist O. C. Marsh first described a Stegosaurus fossil in 1877 he thought the plates lay flat along the back; only after finding a specimen preserved in mud that had held the plates in place did he realize they stood upright, alternating along the spine.
Reputable source · 2 sources - Late Jurassic, about 152 to 145 million years agoAge of Dinosaurs
Sauropods: the largest animals to ever walk the Earth
The sauropods, four-legged plant-eaters with long necks, small heads, and long tails, produced the largest land animals in Earth's history, and several of the best-known lived in the Late Jurassic, about 152 to 145 million years ago, in what is now the United States. Brachiosaurus grew to roughly 22 metres long and weighed around 46,900 kilograms; the Natural History Museum notes that figure may even be an underestimate, since some experts think the known fossil belonged to an animal that was not yet fully grown. Diplodocus grew even longer, around 26 metres, though on a comparatively lighter frame at about 15,000 kilograms. The first Brachiosaurus remains were dug up in Colorado in 1900 by the Chicago paleontologist Elmer S. Riggs, who did not formally name the find until 1903, by which point it was, in his words, the largest dinosaur ever discovered.
Reputable source · 3 sources - 145 to 66 million years agoAge of Dinosaurs
The Cretaceous world and the first flowers
The Cretaceous Period began 145 million years ago and ended 66 million years ago, the last period of the Mesozoic Era and the final act of the age of dinosaurs. During it, flowering plants, known as angiosperms, spread and diversified; today about 90 percent of plant species are flowering plants. This was the world of many of the most famous dinosaurs, a warm planet with no polar ice caps, right up until the moment it ended.
Peer-reviewed · 2 sources - Late Cretaceous, about 99 to 94 million years agoAge of Dinosaurs
Spinosaurus and the aquatic-dinosaur debate
Spinosaurus lived in what is now Egypt and Morocco in the Late Cretaceous, about 99 to 94 million years ago, and at an estimated 14 metres nose to tail, the Natural History Museum calls it longer than any other known carnivorous dinosaur, though it cautions that no complete skeleton exists, so the full length is an estimate. It carried a sail on its back roughly 1.5 metres tall whose purpose is itself unresolved, possibly for temperature regulation, display, or swimming. Fossils show short hind legs and a wide, paddle-like tail, and the museum states outright that whether Spinosaurus actively swam and hunted underwater, or mostly waded and struck from the shoreline, is not settled. A 2022 Natural History Museum report on new supporting evidence still carried on-the-record pushback from outside researchers: Dr David Hone of Queen Mary University of London said the new findings did not resolve doubts about whether the animal could truly dive and swim, even if dense bones let it wade in deeper water.
Peer-reviewed · 3 sources - Late Cretaceous, 74 to 70 million years agoAge of Dinosaurs
Velociraptor: smaller, feathered, and nothing like the movies
Velociraptor lived in what is now Mongolia in the Late Cretaceous, 74 to 70 million years ago, and was, in reality, a small predator: about 1.8 metres long and only around 7 kilograms, a fraction of the size shown in the Jurassic Park films. The Natural History Museum states plainly that the movies recreated Velociraptor at twice its actual size and modeled it closely on a different, larger dinosaur called Deinonychus. Fossil evidence gathered since points to a fine, feather-like covering on the real animal, something no film version has shown.
Peer-reviewed · 2 sources - Late Cretaceous, 68 to 66 million years agoAge of Dinosaurs
Tyrannosaurus rex, the tyrant king
In the final few million years of the Cretaceous, 68 to 66 million years ago, Tyrannosaurus rex hunted across what is now Canada and the United States. It had up to 60 saw-edged teeth, some as long as 20 centimetres, which together with its powerful jaws delivered the strongest bite of any known land animal. The largest known specimens, named Sue and Scotty, weighed over 8,000 kilograms and were almost 13 metres long. The first T. rex skeletons were found by Barnum Brown, in Wyoming in 1900 and at Hell Creek in Montana in 1902, and the species was named by Henry Fairfield Osborn.
Peer-reviewed · 2 sources - Late Cretaceous, 68 to 66 million years agoAge of Dinosaurs
Triceratops locks horns with the tyrant king
Triceratops lived in what is now the United States during the very last few million years of the Cretaceous, 68 to 66 million years ago, sharing its world with Tyrannosaurus rex. It carried three horns, a parrot-like beak, and a bony frill that could reach nearly a metre across, giving it one of the largest and most striking skulls of any land animal, on a body about 9 metres long and roughly 10,000 kilograms. The Natural History Museum points to direct proof that these horns saw combat: a partial Triceratops fossil collected in 1997 has a horn bitten clean off, and the bite marks match Tyrannosaurus.
Peer-reviewed · 2 sources - 66 million years agoBig Bang to Now
The asteroid that ended the dinosaurs
About 66 million years ago, at the end of the Cretaceous Period, an asteroid several kilometers wide slammed into what is now the coast of Mexico, leaving the huge, buried Chicxulub crater. The Natural History Museum calls the result one of the most dramatic mass extinctions Earth has ever seen: the impact threw so much material into the atmosphere that soot and dust darkened the sky worldwide and cut off sunlight, and all non-bird dinosaurs, along with many other groups of animals, died out. The first clue to the cause was a thin layer of iridium, a metal common in asteroids but rare in Earth's rocks, found in rocks from exactly the end of the Cretaceous by Luis and Walter Alvarez in the late 1970s.
Peer-reviewed · 2 sources - 66 million years agoAge of Dinosaurs
The asteroid that ended the dinosaurs
About 66 million years ago, at the very end of the Cretaceous, an asteroid several kilometres wide struck what is now the coast of Mexico, leaving the huge, buried Chicxulub crater. The Natural History Museum calls the result one of the most dramatic mass extinctions Earth has ever seen: the impact hurled so much material into the atmosphere that soot and dust darkened the sky worldwide and cut off sunlight, and all non-bird dinosaurs, along with many other groups, died out. The first clue to the cause was a thin worldwide layer of iridium, a metal rare in Earth's rocks but common in asteroids, found in end-Cretaceous rocks by Luis and Walter Alvarez in the late 1970s.
Peer-reviewed · 2 sources - About 66 million years agoThe Age of Mammals
Purgatorius: the first primate, climbing before it could reason
Among the small mammals that survived the extinction, or appeared in the immediate aftermath, was Purgatorius, a squirrel-sized animal now recognized as the earliest known primate. Its teeth carry an unspecialized, primitive shape typical of early primate ancestors, and its ankle bones show the kind of joint mobility built for climbing among branches rather than moving on the ground. That places Purgatorius, and the earliest primates generally, as tree-dwellers from the start, feeding on fruit and insects in the canopy rather than competing with ground-based mammals below.
Peer-reviewed - From 66 million years ago onwardAge of Dinosaurs
Mammals inherit the Earth
Mammals had existed alongside dinosaurs for most of the Mesozoic, but stayed small and constrained the whole time. That changed the moment the non-bird dinosaurs vanished 66 million years ago. Using 3D scans of 322 mammal skull specimens from more than 20 international museum collections, researchers led by Professor Anjali Goswami at the Natural History Museum traced what happened next: an explosion of diversity among placental mammals immediately after the extinction, with the earliest ancestors of today's living mammal groups appearing in the fossil record within a few hundred thousand years of the impact. The study also found that this initial burst of evolutionary speed was never matched again, slowing steadily in the tens of millions of years that followed.
Peer-reviewed · 2 sources - About 66 to 65 million years agoThe Age of Mammals
Mammals explode in size within a million years of the asteroid
A fossil site at Corral Bluffs, Colorado, dug up layer by layer, gave paleontologists a rare thing: an actual timeline of what happened to mammals right after the asteroid. Immediately after the extinction, the largest mammals were about rat-sized, down from raccoon-sized before the impact. Within 100,000 years they were back to raccoon-sized, but a new kind. By 300,000 years they had grown to beaver-sized, and by 700,000 years after the impact, species like Ectoconus ditrigonus weighed over a hundred pounds, a hundredfold increase in body size from the survivors that started it. Paleontologist Tyler Lyson, who led the study, found that new legume plants growing back after the extinction gave these recovering mammals a richer diet than they'd had before, right alongside the disappearance of the dinosaurs that used to eat them.
Reputable source - 66 million years ago and afterAge of Dinosaurs
Birds: the dinosaurs that survived
Not every dinosaur died with the asteroid. One group came through and is still alive all around us: the birds. Decades of fossil discoveries, especially perfectly preserved feathered dinosaurs unearthed in China from the 1990s onward, convinced researchers that there is a direct link between modern birds and theropod dinosaurs, the same group that included Velociraptor and Tyrannosaurus. Birds are not merely descended from dinosaurs; scientists now regard them as dinosaurs, the one lineage that outlived the extinction.
Peer-reviewed · 2 sources - About 50 million years agoThe Age of Mammals
Pakicetus wades in, and a land mammal starts becoming a whale
Pakicetus looked nothing like a whale. It was a four-legged, hoofed, wolf-sized land mammal that lived and hunted along rivers in what is now Pakistan, and by every outward measure it belonged on land. Its skeleton says otherwise: Pakicetus carries an ear bone structure found nowhere else except in whales, along with an ankle bone shared with even-toed hoofed mammals like modern deer and cattle, tying it directly into the group whales are now known to have descended from. Within about 10 million years, its descendants, culminating in the fully aquatic Dorudon, had lost their legs entirely and completed the move into open water for good.
Reputable source - About 55 to 15 million years agoThe Age of Mammals
Horses trade the forest for the grassland, tooth by tooth
The earliest known horse, Hyracotherium, also called Eohippus, was a fox-sized forest browser around 55 million years ago, standing barely 50 centimetres tall, with four padded, hoofed toes on each front foot and three behind, built for soft forest ground rather than open plains. As global cooling spread grassland savannas across the continents over the following tens of millions of years, horse lineages adapted alongside it. By around 17 to 11 million years ago, Merychippus had become the first true grazing horse, with high-crowned cheek teeth able to withstand the punishing, silica-laden wear of grass, long legs built for outrunning predators across open ground, and a body plan recognizably horse-shaped for the first time, even while still carrying three toes rather than the single hoof of a modern horse.
Reputable source · 2 sources - About 17 to 15 million years agoThe Age of Mammals
Elephants trade a long jaw for a trunk
Early proboscideans, the elephant lineage, fed for millions of years using a long, shovel-like lower jaw rather than a dedicated trunk. A 2024 study of Miocene proboscidean skulls found that as grasslands spread and opened up new habitat, different lineages split into different feeding strategies: Platybelodon kept a shortened lower jaw paired with a strong, flexible trunk suited to cutting plants that grew upright, while Choerolophodon specialized instead in cropping low, horizontally spreading vegetation. Across the elephant lineage as a whole, the study found that the trunk gradually took over feeding entirely, and the long mandible early proboscideans had relied on disappeared.
Peer-reviewed - About 7 to 6 million years agoHuman Evolution
The first steps toward walking upright
The Smithsonian's Human Origins Program traces the oldest evidence for walking on two legs back to two of the earliest known species in the human lineage. Sahelanthropus tchadensis, dated to about 7 to 6 million years ago, may have walked on two legs, based on features of its skull. Around 6 million years ago, Orrorin tugenensis left behind a thigh bone whose upper portion resembles that of other large apes, but whose angled neck closely resembles a modern human's, forming what the Smithsonian describes as a strong bridge with the hip capable of supporting the body's weight while walking upright. For a long stretch afterward, from at least 6 to 3 million years ago, early human ancestors combined apelike and humanlike ways of moving, still capable of climbing trees while increasingly walking upright on the ground.
Peer-reviewed · 2 sources - About 6 million years agoBig Bang to Now
Early humans stand up
One of the very first traits that set our lineage apart from other apes was walking upright on two legs. The Smithsonian's Human Origins Program traces the oldest evidence for it back about 6 million years, to early species such as Sahelanthropus that may have walked on two legs. For millions of years afterward, from at least 6 to 3 million years ago, our ancestors combined apelike and humanlike ways of moving, still climbing trees but increasingly walking upright on the ground, before becoming mostly bipedal by around 4 million years ago.
Peer-reviewed · 2 sources - About 4.4 million years agoHuman Evolution
Ardi overturns the savanna story
Between 1992 and 1994, a team led by paleoanthropologist Tim White found the first Ardipithecus ramidus fossils in the Middle Awash region of Ethiopia, but it was not until 2009 that the team announced their most important find: a partial skeleton nicknamed Ardi, about 4.4 million years old and one of the most complete early human skeletons ever recovered. Ardi's feet had an opposable, grasping big toe alongside more rigid remaining toes, her pelvis was short and broad, and her wrists could bend backward in a way chimpanzees and gorillas, built for knuckle-walking, cannot. Together, the Smithsonian describes this as a mosaic: she could walk upright on the ground while still moving carefully on top of branches using all four limbs, a gait called palmigrady, rather than swinging or knuckle-walking like a chimp.
Peer-reviewed · 3 sources - 24 November 1974Human Evolution
Lucy: forty percent of a skeleton, all the proof of upright walking
On 24 November 1974, at the site of Hadar in Ethiopia, Donald Johanson and his student Tom Gray, working within an expedition that geologist Maurice Taieb helped organize, found a small fossil skeleton later shown to be just under 3.18 million years old. Over two weeks of excavation the team recovered several hundred bone fragments, 47 of which formed a single skeleton representing about 40 percent of one individual, an exceptional proportion for a fossil this old. That night, celebrating at camp while the Beatles' 'Lucy in the Sky with Diamonds' played repeatedly, someone gave the skeleton the name Lucy; its Ethiopian name, Dinkinesh, is Amharic for you are marvelous or you are beautiful, depending on the source. Lucy's thigh bone, pelvis, and vertebrae all show adaptations the Smithsonian and the Institute of Human Origins describe as clear evidence of habitual upright walking, including a pelvis remodeled to balance the trunk over one leg at a time and a spine curved the way a modern human's is.
Reputable source · 3 sources - About 2.6 million years agoHuman Evolution
The first stone tools: the Oldowan toolkit
By about 2.6 million years ago, early humans were deliberately shaping stone into tools. The Smithsonian's Human Origins Program describes this earliest toolkit, the Oldowan, as the most basic stone implements our ancestors made: hammerstones used to strike other rocks, the stone cores those strikes came from, and the sharp flakes knocked off in the process. Toolmaking then continues across the roughly 2.6 million years since, spanning thousands of excavated archaeological sites that have been studied and dated, an unbroken technological record from a chipped stone flake to the device this sentence is being read on.
Peer-reviewed · 2 sources - About 2.6 million years agoBig Bang to Now
The first stone tools
By about 2.6 million years ago, early humans were deliberately making the first stone tools. The Smithsonian describes this earliest toolkit, known as the Oldowan, as the most basic stone implements: hammerstones, stone cores, and the sharp flakes struck off them, which could cut and scrape in ways bare hands could not. Toolmaking then spans the whole 2.6 million years since, a record that runs unbroken from a chipped stone flake all the way to the device you are reading this on.
Peer-reviewed · 2 sources - About 1.89 million to 110,000 years agoHuman Evolution
Homo erectus builds a body for the long walk
Homo erectus lived from about 1.89 million years ago to as recently as 110,000 years ago, and the Smithsonian's Human Origins Program calls its earliest African fossils the oldest known early humans with modern human-like body proportions: relatively elongated legs and shorter arms compared to the torso, an adaptation for a life spent on the ground rather than in trees, built for walking and possibly running long distances. Individuals ranged from about 4 feet 9 inches to 6 feet 1 inch tall. A remarkably complete skeleton found in East Africa, an eight- to nine-year-old boy who lived about 1.6 million years ago and stood 1.6 metres tall, shows the same tall, lean build adapted to hot, dry environments. Homo erectus is generally considered the first early human species to expand beyond Africa, reaching Western Asia and as far as China and Indonesia, though whether it reached Europe remains uncertain.
Peer-reviewed · 3 sources - By about 790,000 years ago (earlier use debated)Human Evolution
The control of fire
The Smithsonian describes the oldest definite control of fire at about 790,000 years ago, in the form of fire-scorched stone toolmaking debris and burned seeds and wood marking early hearths at Gesher Benot Ya'aqov in Israel, a site excavated by a team led by Naama Goren-Inbar and reported in 2004. The Smithsonian's own pages are careful to distinguish this from older, less certain claims: it notes that some researchers think cooking may reach back more than 1.5 million years, within the long span of Homo erectus, but frames that earlier date as a minority view rather than settled fact, and lists how well Homo erectus actually mastered fire as one of the field's genuinely open questions.
Peer-reviewed · 4 sources - About 400,000 to 40,000 years agoHuman Evolution
Neanderthals: our closest, and only interbred, relative
Neanderthals lived across Europe and southwestern to central Asia from about 400,000 to 40,000 years ago, and the Smithsonian's Human Origins Program calls them our closest extinct human relative. They had a large mid-face, angled cheekbones, and a large nose suited to warming and humidifying cold, dry air, on bodies shorter and stockier than a modern human's, and brains just as large as ours, often larger relative to their heavier build. They made sophisticated tools, controlled fire, built shelters, wore clothing, hunted large animals, and sometimes made symbolic objects; there is evidence they deliberately buried their dead, occasionally with grave offerings such as flowers. Neanderthals and Homo sapiens shared a common ancestor between about 700,000 and 300,000 years ago, and the two species inhabited the same parts of western Asia for 30,000 to 50,000 years, a period during which genetic evidence shows they interbred before Neanderthals disappeared from the fossil record entirely by about 40,000 years ago.
Peer-reviewed · 3 sources - About 300,000 years agoBig Bang to Now
Homo sapiens appears
Our own species, Homo sapiens, evolved in Africa about 300,000 years ago, according to the Smithsonian, and every person alive today belongs to it. For most of that time our ancestors lived across Africa; only much later did they spread out to populate the rest of the planet, until the species that started on one continent now lives worldwide. We are, in the long view of this timeline, a very young kind of animal.
Peer-reviewed · 2 sources - About 300,000 years ago (discovery published 8 June 2017)Human Evolution
Jebel Irhoud pushes Homo sapiens back 100,000 years
Homo sapiens evolved in Africa during a period of dramatic climate change about 300,000 years ago, a date fixed by fossils from Jebel Irhoud cave in Morocco that are now considered the oldest known members of our species. Published in the journal Nature on 8 June 2017 by Jean-Jacques Hublin and colleagues, the find pushed back the origin of Homo sapiens by at least 100,000 years from what had previously been accepted. The fossils show large teeth and a long braincase similar to earlier species like Neanderthals, but a face, forehead, and jawbone much closer to a modern human's. The Smithsonian notes the finds suggest our species evolved across a wide area of Africa, with early populations interacting and evolving for hundreds of thousands of years before any dispersal beyond the continent. Anatomically, later Homo sapiens are marked by a lighter skeleton, a large brain averaging about 1,300 cubic centimetres, a thin-walled, high, rounded skull, and a flatter, more vertical face with smaller teeth and jaws than earlier humans.
Peer-reviewed · 3 sources - About 77,000 to 75,000 years agoHuman Evolution
The Blombos ochre: the first symbol
In 1991, at Blombos Cave in South Africa, archaeologist Christopher Henshilwood found a piece of ochre, about 77,000 to 75,000 years old, bearing deliberately incised, geometrically organized cross-hatched markings. The Smithsonian's Human Origins Program describes the pattern as clearly organized rather than random, which suggests to researchers that the markings represent stored information rather than decoration made without a plan.
Peer-reviewed · 2 sources - At least 50,200 years agoHuman Evolution
A hunting scene painted at least 50,000 years ago
In a cave called Leang Bulu' Sipong 4 on the island of Sulawesi, Indonesia, researchers found a large painted panel depicting a narrative hunting scene: wild pigs and small buffalo-like animals called anoas pursued by human-like figures carrying spears and ropes, several of which show non-human features. A 2024 study published in Nature, using a more precise uranium-series imaging technique, dated the scene to a minimum of 50,200 years, revising an earlier 2019 estimate of 43,900 years upward by more than 4,000 years. The same study reported an even older painting at a nearby cave, Leang Karampuang, with a minimum age of 51,200 years, the figure that gives the paper its title and now stands as the oldest known narrative cave art. The researchers interpret the hybrid figures as therianthropes, composite human-animal beings, rather than straightforward portraits of hunters.
Peer-reviewed - At least 21,000 to 23,000 years agoHuman Evolution
Footprints at White Sands push back the peopling of the Americas
At White Sands National Park in New Mexico, researchers announced in September 2021 that fossilized human footprints in the Tularosa Basin dated to at least 23,000 years old, thousands of years earlier than the roughly 13,500 to 16,000 year arrival previously accepted by most archaeologists. The National Park Service reports the calibrated radiocarbon dates as 22,860 and 21,130 years, derived from seed layers above and below the footprint layer. The finding meant humans were present in North America before the height of the last ice age closed the migration routes from Asia, extending the known period during which people coexisted with Ice Age megafauna. The U.S. Geological Survey states plainly that the original announcement sparked dissenting commentary throughout the scientific community, but a 2023 follow-up study using two additional, independent dating methods reproduced the same 21,000 to 23,000 year range, which the USGS says makes it highly unlikely all three lines of evidence are wrong.
Reputable source · 3 sources - About 20,000 to 19,000 years agoThe Neolithic Revolution
Pottery is invented, thousands of years before farming
The story that ends in cities begins with a technology that came long before any of them, and before farming itself. The oldest known pottery, from Xianrendong Cave in Jiangxi Province, China, is radiocarbon-dated to about 20,000 to 19,000 years ago, and, as the excavators state, it was produced by mobile foragers who hunted and gathered during the height of the last Ice Age, probably to cook food. The Smithsonian likewise dates the oldest East Asian pottery to roughly 18,000 years ago. This was made and used, in the researchers' own words, ten millennia or more before the emergence of agriculture.
Peer-reviewed · 2 sources - About 12,000 years agoBig Bang to Now
Farming begins
Beginning about 12,000 years ago, people in several parts of the world independently began to domesticate plants and animals rather than only hunting wild game and gathering wild plants. World History Encyclopedia describes the first crops and livestock being domesticated across roughly six separate regions, including the Near East, China, Southeast Asia, and Africa. This shift, often called the Neolithic Revolution, unfolded over generations rather than overnight.
Peer-reviewed · 2 sources - About 9,600 to 8,200 BCE (roughly 11,500 years ago)The Neolithic Revolution
Gobekli Tepe: monuments before farming
On a hilltop in the Germuş mountains of southeastern Turkey, excavators uncovered massive carved stone pillars, arranged in circular and oval enclosures, dated by UNESCO to between 9,600 and 8,200 BCE, roughly 11,500 years ago and about 6,000 years before Stonehenge. Each ring centers on two T-shaped limestone pillars, some towering 16 feet and weighing seven to ten tons, surrounded by smaller pillars facing inward, many carved with foxes, lions, scorpions, and vultures. Excavation found the site's bones were overwhelmingly from wild game, not livestock, meaning the people who built it had not yet domesticated animals or crops.
Reputable source · 2 sources - About 11,500 to 8,500 years ago (roughly 9500 to 6500 BCE)The Neolithic Revolution
Wheat and barley stop scattering their own seed
Long before farming as we would recognize it, people in the Fertile Crescent, especially in what is now southeast Turkey and northern Syria, were cultivating wild einkorn wheat, emmer wheat, and barley. Peer-reviewed genetic research traces the moment these became true domesticated crops to a specific change: wild grass seed heads shatter and scatter their grain naturally, a trait called a brittle rachis, but a mutation produced a non-brittle rachis that kept the grain attached to the plant instead of falling to the ground. That single change meant the plant now depended on people to harvest and replant it. Archaeological evidence places pre-domestication cultivation as early as about 11,500 years ago, with the non-brittle trait becoming dominant in the archaeological record roughly a thousand years or more later, and genetic studies trace the origin of the domesticated trait to the same part of southeast Turkey across both einkorn and barley.
Peer-reviewed · 3 sources - By about 8,200 BCEThe Neolithic Revolution
Goats become livestock in the Zagros Mountains
In the Zagros Mountains of western Iran, at a site called Ganj Dareh, researchers combined two kinds of evidence to establish that goats were being managed as livestock, not simply hunted, by about 8,200 calibrated years BCE. The first is demographic: at wild-hunted sites, kills skew toward large adult males, but at Ganj Dareh 60 to 70 percent of male goats were culled young, before two and a half years old, while most females were kept alive well past that age, with females outnumbering males by as much as nearly two to one across every layer of the site, exactly the pattern of a herd being managed for milk and breeding rather than only meat. The second is genetic: ancient DNA from these goats shows signs of captive breeding and shared ancestry with later domestic populations, described by the research team as the oldest confirmed livestock genomes reported to date. In the same layers, sheep bones still showed the profile of a wild, hunted resource, showing that even within one site, goats and sheep were not domesticated on the same timeline.
Peer-reviewed · 2 sources - By about 8000 BCEThe Neolithic Revolution
Jericho raises the world's oldest known wall
Jericho's earliest settlements, drawn by natural springs that could sustain a large population in an otherwise dry landscape, date back to about 9000 BCE. By 8000 BCE the site had grown to about 40,000 square metres, encircled by a stone wall 3.6 metres high and 1.8 metres wide at its base, which World History Encyclopedia calls the oldest known protective wall in the world. Inside that wall stood a stone tower 8.5 metres high and 9 metres wide at its base, built solid enough to contain an internal staircase of 22 steps. Continuing excavation has since turned up stone towers elsewhere that are even older, at a site called Tell Qaramel.
Peer-reviewed · 2 sources - About 7,400 to 6,200 BCEThe Neolithic Revolution
Catalhoyuk: a town with no streets
At Catalhoyuk in central Turkey, a Neolithic settlement grew from its first occupation around 7,400 BCE and lasted through about 6,200 BCE, rebuilt on the same spot many times over that span. UNESCO's World Heritage listing calls it a unique streetless settlement: rectangular mudbrick houses were built directly against each other with no streets or alleys between them, and people moved across the rooftops, entering their homes by climbing down a ladder through an opening in the ceiling rather than through a door. At its peak, the excavation project estimates the town held between 3,500 and 8,000 people, and the site is described as illustrating the transition from scattered villages to genuine urban centers, apparently organized on largely egalitarian lines rather than around a ruling elite.
Peer-reviewed · 3 sources - By about 8,700 years ago (roughly 6700 BCE)The Neolithic Revolution
Maize is domesticated in Mexico, a New World origin of farming
Farming was not a single event that spread from one place; it arose independently in several parts of the world, and the clearest proof is in the Americas. In the Central Balsas River Valley of southern Mexico, people domesticated maize from a wild grass called teosinte, specifically Balsas teosinte. Starch grains and phytoliths recovered from grinding tools at the Xihuatoxtla shelter show maize was present there by about 8,700 years ago, and genetic analysis of hundreds of plants independently points to a single domestication in southern Mexico around 9,000 years ago, from teosinte of the Balsas drainage. The researchers note this happened at about the same time as, but entirely separately from, the rise of farming in the Old World.
Peer-reviewed · 3 sources - Rice by about 6700-6300 BCE; millet by about 5800 BCEThe Neolithic Revolution
China domesticates rice and millet, two more independent origins
China gave rise to two more independent farming traditions, split between two great river systems. In the warm, wet Middle and Lower Yangtze valley of the south, people domesticated rice: archaeobotanical evidence shows already-domesticated rice, marked by non-shattering spikelet bases, in the middle Yangtze by about 6700 to 6300 BCE. In the cooler, drier Yellow River valley of the north, the founder crops were millets, chiefly broomcorn millet, cultivated by the Peiligang culture by about 5800 BCE. Researchers describe these as separate northern-millet and southern-rice traditions that only later met and mixed, as rice spread north and millet spread south, by around 4000 BCE.
Peer-reviewed · 2 sources - From about 6500 BCE across the following two millenniaThe Neolithic Revolution
Farming spreads into Europe, carried by migrating farmers
Farming reached Europe from the Near East, and ancient DNA has settled a long argument about how. By about 6500 BCE, settled farming villages were established in northwestern and coastal Anatolia, on the threshold of Europe. Genome-wide DNA from early farmers on both sides of the Aegean then revealed an unbroken chain of ancestry linking farmers across central and southwestern Europe back to Greece and northwestern Anatolia. As the study puts it, this is decisive evidence against the idea that farming spread into Europe as ideas alone, without migration of people. The same signature carried deeper into the continent with the Linear Pottery (LBK) culture, which rooted in Hungary about 7,500 to 8,000 years ago and spread within a few centuries as far as the Paris Basin, its farmers genetically distinct from the local hunter-gatherers and carrying substantial Near Eastern ancestry.
Peer-reviewed · 3 sources - Around 3500 BCEBig Bang to Now
The first cities and writing
In the cities of Sumer, in southern Mesopotamia, writing was invented around 3600 to 3500 BCE, and World History Encyclopedia locates the earliest true writing in the Sumerian city of Uruk. It began as pictographs, simple symbols standing for objects, pressed into wet clay with a reed to keep track of goods and accounts. Over time those pictures gave way to phonograms, marks that stood for sounds, in the script we call cuneiform, and writing grew from a bookkeeping tool into a way to record law, story, and history.
Peer-reviewed · 2 sources - The Uruk Period, about 4000 to 3100 BCE, writing by about 3200 BCEThe Neolithic Revolution
Uruk: the first city, and the first writing
In the Uruk Period, roughly 4000 to 3100 BCE, cities began to develop across Mesopotamia for the first time, and World History Encyclopedia identifies Uruk, in the southern region of Sumer, in what is now Warka, Iraq, as the most important and influential of them, the largest urban center and the hub of regional trade and administration between about 4100 and 3000 BCE. Uruk is credited with a run of firsts: the origin of the ziggurat, the invention of the cylinder seal used to mark property and sign documents, and, most consequentially, the further development of cuneiform writing by about 3200 BCE. Writing began as pictographs, simple pictures representing objects, pressed with a stylus into wet clay to record temple accounts, such as deliveries of sheep, before evolving into phonograms, symbols that could represent sounds and eventually record language itself, including the city's own later literary tradition centered on its king Gilgamesh.
Peer-reviewed · 3 sources - 1760 to 1840Big Bang to Now
The Industrial Revolution
Between about 1760 and 1840, beginning in Britain, work moved out of the home and the workshop and into factories built around steam-powered machines. World History Encyclopedia describes the mechanization of production and the deep social change that came with it, as people crowded from the countryside into fast-growing industrial cities to run and tend the new machines. Earlier gains in agriculture had freed up labor, and that labor now poured into manufacturing.
Peer-reviewed · 2 sources - 1811 to 1823Age of Dinosaurs
Mary Anning finds the sea's monsters
Mary Anning was born in 1799 in Lyme Regis, on England's Jurassic Coast, and became one of the most consequential fossil hunters in the history of the science, working outside the scientific establishment of her time. In the autumn of 1811, when she was twelve, she and her brother Joseph found Britain's first identified ichthyosaur skeleton. In December 1823 she went further, discovering the first complete skeleton of a Plesiosaurus, a marine reptile whose name means near to reptile. The find was so strange that a special meeting was called at the Geological Society of London to examine it, and the French anatomist Georges Cuvier initially doubted it was even genuine, suspecting a fabrication, before further evidence convinced him it was real. Anning herself was not invited to that meeting about her own discovery. She died of breast cancer in 1847, still in financial strain despite a lifetime of major scientific finds.
Reputable source · 2 sources - 1842Age of Dinosaurs
Richard Owen coins the word 'dinosaur'
Until 1842, no one had heard the word dinosaur. The anatomist Richard Owen examined three fossil finds made by other collectors over the previous two decades, Megalosaurus, described by William Buckland in 1824, and Iguanodon and Hylaeosaurus, both described by Gideon Mantell in 1825 and 1833, and recognized shared features linking them as a distinct group unlike any living reptile. He first laid out the idea in a lecture to the British Association in July 1841 that reportedly ran two hours, then formally coined the term Dinosauria in his published report the following year. The Natural History Museum notes that the name is often translated from Greek as terrible lizard, but that Owen himself described the animals instead as fearfully great, a term aimed squarely at their scale rather than their ferocity.
Reputable source · 2 sources - 1977 to 1978Age of Dinosaurs
Egg Mountain: the first evidence dinosaurs cared for their young
In 1977, Marion Brandvold, who ran a small rock shop in Bynum, Montana, found the remains of juvenile dinosaurs and showed them the next year to paleontologist Jack Horner. Horner and his team, working in the Two Medicine Formation, went on to uncover 14 dinosaur nests in a single area, a site that became known as Egg Mountain. Alongside eggs and broken eggshells, they found an adult skeleton in close association with a nest of young dinosaurs about a metre long, and hatchlings too large to have just emerged from an egg. A peer-reviewed study of the specimens found their bones were not fully developed, or ossified, meaning the young could not have walked immediately after hatching and would have needed care from an adult. The species was named Maiasaura, meaning good mother lizard.
Peer-reviewed · 2 sources - The present, 2026Big Bang to Now
Now: the moment you are reading this
Here the timeline reaches you. In the thin slice of time between the first stone tools and this morning, one species learned to farm, to write, to build machines, and then to turn its instruments on the sky and measure the age of the universe itself, 13.8 billion years, and lay the whole story out on a single line you can zoom. You are reading this at the very near end of everything above, in a present that is still being written.
Reputable source