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About 4.567 billion years agoReputable source · 2 sourcesWell documented

The oldest solids we can date: 4.567 billion years

On the timeline · around About 4.567 billion years ago · Building the PlanetsNebula and SunBuilding the PlanetsThe oldest solids we can date: 4.567 billion years4.6 Ga4.6 Ga4.6 Ga4.6 Ga4.6 Ga4.6 Ga

What happened

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.

Sources

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Part of a timelineThe Formation of the Solar System11 events · 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.View all →
The oldest solids we can date: 4.567 billion years · The Formation of the Solar System · SourcedStory