The Formation of the Solar System
The 800 million years that turned a collapsing cloud of gas into the Sun, the planets, and a habitable Earth, from the oldest solids we can date to the first oceans.
A zoom into the deep-time opening of the Big Bang to Now spine: how the Solar System and the Earth formed between about 4.6 and 3.9 billion years ago. It runs from the collapsing cloud that became the Sun, through the oldest datable solids, the giant planets and the asteroid belt they carved, the accretion of the rocky worlds, the giant impact that made the Moon, the layered core and magnetic shield, the oldest surviving crystal and rock, the first oceans, and the disputed Late Heavy Bombardment. Every event is built from content-verified sources: NASA, the U.S. Geological Survey, the Geological Survey of Canada, national laboratories, and peer-reviewed papers in Nature, Scientific Reports, and the Annual Review of Earth and Planetary Sciences.
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- About 4.6 billion years agoWell documented
Reputable sourcewhy?
Best source: How did our Solar System form?
The domain "science.nasa.gov" is on our Reputable source registry.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.
Why it matters: The gas and dust that did not fall into the Sun stayed behind as a spinning disk. Every planet, moon, asteroid, and comet, the Earth included, was built from that disk, out of the exact mix of elements the original cloud held.
How we know: The composition of the cloud survives in the oldest meteorites, whose element mix closely tracks the Sun's outer layers. The supernova trigger is the explanation NASA gives for what set a slowly turning cloud collapsing, and the flat, one-directional layout of the planets' orbits today still records that early spinning disk.
SourcesRelated timelines- Big Bang to Now → · Zoomed out: this is the spine's 'The Sun and Solar System form'
- About 4.567 billion years agoWell documented
Reputable source · 2 sourceswhy?
Best source: Refractory Inclusions
The domain "earthsciences.anu.edu.au" is on our Reputable source registry.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.
Why it matters: CAIs are the clock everything else is measured against. Dating them fixed a firm zero point, so the ages of meteorites, the Moon, and the Earth are all quoted relative to that 4.567-billion-year start.
How we know: The ages come from radioactive decay locked inside the grains: uranium turns to lead at a known rate, so the ratio of lead isotopes in a CAI records how long ago it crystallized. Different laboratories dating different meteorites land on the same 4,567-million-year figure.
- About 4.56 billion years agoWell documented
Peer-reviewed · 2 sourceswhy?
Best source: Terrestrial planet and asteroid belt formation by Jupiter-Saturn chaotic excitation
Cited as a "journal" source (no stronger domain match).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.
Why it matters: The giants set the boundary conditions for the rocky planets. The same stirring that emptied the asteroid belt is a leading explanation for why Mars is only about a tenth of Earth's mass, and it limited how much material Earth itself could gather.
How we know: The asteroid belt is the standing evidence: a zone of rocky bodies between Mars and Jupiter that never became a planet, which NASA attributes to Jupiter's gravity. The Scientific Reports model reproduces both that emptied belt and Mars's small mass from Jupiter and Saturn's early orbits, without the more extreme migration some rival models require.
- About 4.55 billion years agoWell documented
Reputable sourcewhy?
Best source: How did our Solar System form?
The domain "science.nasa.gov" is on our Reputable source registry.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.
Why it matters: Accretion explains why the Solar System is sorted the way it is, rocky worlds near the Sun and gas giants beyond. Earth sits in the inner zone because that is the only place its iron-and-silicate recipe could come together.
How we know: The rocky-inner, gas-giant-outer pattern is exactly what the disk's temperature gradient predicts, and it matches the Solar System we observe. The leftover planetesimals that never joined a planet still orbit today as asteroids and comets.
Sources - About 4.54 billion years agoWell documented
Reputable sourcewhy?
Best source: Age of the Earth
The domain "pubs.usgs.gov" is on our Reputable source registry.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.
Why it matters: That one number anchors all of geology and much of biology. Every later date on this timeline and the others, from the first oceans to the first humans, is measured against an Earth that is 4.54 billion years old.
How we know: Earth's own surface has been recycled by plate tectonics, so no rock survives from its birth. Meteorites were never recycled, so the lead-isotope clock inside them still reads the moment the Solar System's material formed, which is taken as the age of the Earth.
Sources- U.S. Geological Survey. Age of the Earth · reference
Related timelines- Big Bang to Now → · Zoomed out: this is the spine's 'Earth forms'
- About 4.5 billion years agoWell documented
Peer-reviewed · 2 sourceswhy?
Best source: Origin of the Moon in a giant impact near the end of the Earth's formation
Cited as a "journal" source (no stronger domain match).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.
Why it matters: The impact set Earth spinning fast and left it with an unusually large Moon. Over billions of years that Moon has steadied Earth's tilt and raised the tides, both of which shaped the environments life later evolved in.
How we know: The strongest evidence is the Apollo Moon rocks, whose oxygen isotopes match Earth's and whose chemistry shows a body once molten and short on iron. Simulations of a Mars-sized impact reproduce the angular momentum of the Earth-Moon system, though matching those near-identical isotopes exactly is still an open problem, known as the lunar isotopic crisis.
SourcesRelated timelines- Big Bang to Now → · Zoomed out: this is the spine's 'The giant impact that made the Moon'
- About 4.5 billion years agoWell documented
Reputable source · 2 sourceswhy?
Best source: Facts About Earth
The domain "science.nasa.gov" is on our Reputable source registry.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.
Why it matters: The magnetosphere shields the atmosphere from the solar wind, the stream of charged particles the Sun constantly throws off, which would otherwise strip the air away over time. Stable air and oceans are far harder to keep on a rocky planet with no magnetic shield, so this layering is part of what kept early Earth habitable.
How we know: NASA gives the iron-and-nickel core in its measured dimensions and ties Earth's magnetic field directly to that rotating molten core. The magnetosphere the field creates is not merely inferred, it is mapped, flown through and measured by spacecraft.
Sources - About 4.4 billion years agoWell documented
Peer-reviewed · 2 sourceswhy?
Best source: Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago
Cited as a "journal" source (no stronger domain match).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.
Why it matters: The zircons pushed the date for a cool, wet, potentially habitable Earth back to within about 150 million years of the planet's formation. That moved the earliest possible window for life much closer to Earth's birth than anyone had assumed.
How we know: The age comes from uranium-lead dating of the zircon, a mineral tough enough to outlast the destruction of its parent rock. The water signal comes from the oxygen-isotope ratio measured in the same grain. Both readings sit on one crystal, which is how a single surviving mineral can testify to conditions no rock records.
- By about 4.4 billion years agoWell documented
Reputable source · 2 sourceswhy?
Best source: What was the Earth like right after it formed?
The domain "science.nasa.gov" is on our Reputable source registry.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.
Why it matters: Liquid water is the one ingredient every known form of life requires. Once Earth held stable oceans, it had the setting in which the chemistry that leads to life could begin.
How we know: The volcanic-outgassing and impact-delivery routes are what NASA describes for the origin of the air and seas. The timing is fixed by the 4.4-billion-year-old Jack Hills zircons, whose oxygen isotopes require liquid water to have already been in contact with rock.
SourcesRelated timelines- Big Bang to Now → · The wet, cooling Earth that leads into the spine's 'Life begins on Earth'
- About 4.03 billion years agoWell documented
Reputable sourcewhy?
Best source: Acasta Gneiss (1983)
The domain "science.gc.ca" is on our Reputable source registry.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.
Why it matters: The Acasta Gneiss is where Earth's crust stops being a story told only by loose crystals and becomes rock we can hold and map. It is the oldest surviving piece of a continent, the start of the continuous geological record.
How we know: As with the Jack Hills grains, the age comes from uranium-lead dating of zircons, which lock in the date they crystallized and resist later disturbance. The rock's place in the Slave craton ties it to the oldest stable block of continental crust in North America.
Sources - Around 4 to 3.9 billion years ago (disputed)Debated
Peer-reviewed · 2 sourceswhy?
Best source: The Late Heavy Bombardment
Cited as a "journal" source (no stronger domain match).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.
Why it matters: Whether the bombardment was a real spike bears directly on life's timeline. A late cataclysm could have sterilized or reset the surface just before the earliest signs of life; a gradual tapering of impacts would instead have left early life a calmer window to take hold.
How we know: The evidence is radiometric ages of impact-melt rocks from the Apollo missions. The dispute is a sampling problem: lunar meteorites from a wider spread of the Moon show impact ages more spread out in time, which weakens the case for a tight 4-billion-year spike. Researchers now argue variously that the bombardment was gradual, came in segments, or never happened as a distinct event.
SourcesRelated timelines- Big Bang to Now → · Just before the spine's 'Life begins on Earth'