Life › Origin of life
Formation of Earth
4.54 billion years ago· Event· Earth, climate & extinctions
Well establishedStrong fossil, genetic or geological evidence.
Earth assembled from dust and rock circling the young Sun about 4.54 billion years ago.
See it on the Life map →What happened
The Sun formed inside a spinning disk of gas and dust. In that disk, grains clumped into boulders, then into small planets that kept colliding. Earth grew this way over roughly 10–100 million years, heated by impacts and radioactivity until much of it melted. Heavy iron sank to form the core; lighter rock rose to form the mantle and crust. This first eon, the Hadean, was hot and battered. The Curious Science map covers how stars and planets form.
Why it matters
Every later event on this map happened here. Earth's size, distance from the Sun and iron core, which powers a protective magnetic field, set the limits for life.
The evidence (fossils, genes, rocks)
Radioactive dating of meteorites, leftover building blocks of the solar system, by Clair Patterson in 1956; zircon crystals from Jack Hills, Australia, about 4.4 billion years old, are the oldest known Earth material.
Still debated
How quickly Earth assembled, and where its water and carbon came from, are still argued.
Inside this (4)
Connections (3)
▸Formation of Earth was soon followed by Giant impact forms the MoonStrong evidence
The connection
While Earth was still growing, within perhaps tens of millions of years of its start, a Mars-sized body struck it at an angle. The blast melted Earth's surface and threw rock into orbit, which gathered into the Moon. The impact also likely set Earth's fast early spin and may have tilted its axis.
When and how
About 4.5 billion years ago in the inner solar system; proposed by William Hartmann and Donald Davis in 1975 and by Alastair Cameron and William Ward in 1976.
How sure are we?
Apollo moon rocks match Earth's oxygen isotopes almost exactly; the Moon has little iron; computer simulations reproduce the Earth–Moon spin and orbit.
Debates and open questions
The exact timing (estimates run from about 4.51 to 4.35 billion years ago) and Theia's size are debated; some models use several smaller impacts instead.
▸Formation of Earth cooled enough to hold Water & the first oceansStrong evidence
The connection
As impacts slowed and the molten surface cooled and hardened, water vapor from volcanoes and from water locked in Earth's building blocks condensed. Rain fell and pooled into oceans. A thick carbon dioxide atmosphere probably kept them liquid even though the young Sun was about 25–30% dimmer than today.
When and how
Within roughly 150 million years of Earth forming; key zircon evidence from Jack Hills, Western Australia, published in 2001 by separate teams led by Simon Wilde and Stephen Mojzsis.
How sure are we?
Zircons 4.4 billion years old carry oxygen isotope ratios suggesting contact with liquid water; 3.8-billion-year-old pillow lavas in Greenland formed underwater.
Debates and open questions
How much water came from Earth's own rock versus later asteroids, and whether big impacts boiled early oceans away before they re-formed.
▸Clair Patterson dates the Earth measured the age of Formation of EarthWell established
The connection
Earth's surface has been recycled, so its earliest rocks are gone. Patterson assumed that meteorites formed at the same time from the same material, and that lead in ocean sediments represents Earth's average. Both fell on one uranium-lead age line at 4.55 billion years, dating Earth's formation itself rather than its oldest surviving rocks.
When and how
Measured in 1953 at Argonne National Laboratory near Chicago, with Patterson based at Caltech; published in 1956 in the journal Geochimica et Cosmochimica Acta.
The evidence
Later meteorite dates, Moon rocks from Apollo and 4.4-billion-year-old zircon crystals from Western Australia all fit; today's figure is 4.54 billion years, plus or minus 50 million.
Debates and open questions
Earth grew over tens of millions of years, so 'formation' is a span, not a moment; when the Moon-forming impact happened within that span is still debated.