Geology
The first oceans
Earth cools enough for rain to stay
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Zircon crystals from Jack Hills in Australia, dated to 4.4 billion years, carry isotopic signatures suggesting they formed in contact with liquid water. That water came both from outgassing of Earth's interior and from comets and asteroids. The ocean is not only where life could begin: it is also an enormous heat reservoir that has damped climate swings throughout Earth's history.
For children
When Earth finally cooled enough, the water vapour in the air could turn into droplets. It rained and rained for thousands of years, and the water gathered in hollows on the surface. That is how Earth got its first oceans — and its blue colour.
Connects to
Part of Terra Saga — the story of Earth on a timeline. terrasaga.org