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Birth of the Sun and Earth
Sun c. 4.6 billion years ago; Earth c. 4.54 billion· Event· Universe & Earth
Well documentedSolid records, physical evidence or scientific consensus.
The Sun formed from a collapsing cloud of gas and dust about 4.6 billion years ago; Earth grew from the leftovers.
See it on the History map →What happened
A cloud enriched by earlier stars collapsed, perhaps nudged by a nearby exploding star. Most of the material became the Sun. The rest formed a spinning disk where dust clumped into rocks, then into planets. Earth took shape about 4.54 billion years ago, hot and battered by impacts; its iron sank to form the core. The Curious Science and Curious Life maps go deeper.
Why it matters
Earth's distance from the Sun lets water stay liquid, and its size holds an atmosphere. Every later event on this map happened here.
How we know
Radioactive dating of meteorites by Clair Patterson in 1956 gives the solar system's age; zircon crystals from Jack Hills, Australia, about 4.4 billion years old, are the oldest known Earth material.
Still debated
Where Earth's water came from (comets, asteroids or the original dust) and how fast Earth assembled are still debated.
Inside this (1)
Connections (4)
▸Forging of heavy elements in stars supplied the raw material for Birth of the Sun and EarthWell documented
The connection
By 4.6 billion years ago, generations of stars had seeded our region's gas with iron, silicon, oxygen and other heavy elements. The cloud that formed the solar system held only about 2 percent of them, but that was enough to build rocky planets like Earth, with its iron core and stony crust.
When and how
In the Milky Way's disk, before and during the solar system's birth about 4.6 billion years ago.
How we know
Meteorites contain traces of short-lived radioactive atoms, such as aluminum-26, that must have come from a nearby star shortly before the solar system formed.
Debates and open questions
Whether a nearby exploding star actually triggered the cloud's collapse, or only enriched it, is debated.
▸The Milky Way galaxy was the setting for Birth of the Sun and EarthWell documented
The connection
The solar system formed in the Milky Way's disk, from a cloud enriched by billions of years of star births and deaths. Its location, roughly halfway out from the center, offered enough heavy elements for rocky planets and fewer nearby blasts than the crowded core.
When and how
About 26,000 light-years from the galaxy's center, 4.6 billion years ago, probably in a cluster of sibling stars that later scattered.
How we know
The Sun's chemistry fits the galaxy's pattern for its age and position; astronomers have identified possible sibling stars with nearly identical chemistry.
Debates and open questions
Where the Sun was actually born is uncertain; it may have drifted outward from a birthplace nearer the center.
▸Birth of the Sun and Earth was soon followed by Birth of the MoonMostly agreed
The connection
In the crowded early solar system, Earth was still growing through collisions. Within roughly 100 million years of the solar system's start, a body about the size of Mars, called Theia, struck it. Debris thrown into orbit around Earth gathered into the Moon.
When and how
In the inner solar system, about 4.5 billion years ago; the giant-impact idea was proposed by William Hartmann and Donald Davis in 1975.
How sure are we?
Apollo rocks show the Moon shares Earth's oxygen 'fingerprint' and has little iron, as an impact that blasted off Earth's outer layers would produce.
Debates and open questions
The exact timing (estimates run from about 4.51 to 4.35 billion years ago) and why Theia left so little chemical trace are debated.
▸Birth of the Sun and Earth provided water and chemistry for First lifeMostly agreed
The connection
Earth formed at a distance from the Sun where water stays liquid. Its water, perhaps from water-bearing rocks and comets, pooled into oceans. Volcanoes, minerals, lightning and sunlight supplied energy and raw chemicals. Within a few hundred million years of the surface cooling, life appeared in this setting.
When and how
On Earth, between about 4.4 billion years ago, when oceans may already have existed, and 3.5 billion years ago.
How sure are we?
Zircon crystals about 4.4 billion years old suggest liquid water existed early; fossil microbes about 3.5 billion years old show life followed.
Debates and open questions
Where Earth's water came from, and how quickly life followed once conditions allowed, are debated.