Earth gets its oceans and first atmosphere
What happened
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.
Sources
- NASA (Astrobiology Program). What was the Earth like right after it formed? (2024) · Reputable sourcescience.nasa.gov · The domain "science.nasa.gov" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- NASA Astrobiology. Earth's Oldest Mineral Grains Suggest an Early Start for Life · Reputable sourceastrobiology.nasa.gov · The domain "astrobiology.nasa.gov" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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