ATMOSPHERE × EARTH
Earth's First Atmosphere
~4.45 to 4.3 billion years ago
The Earth's first atmosphere was made of vaporised rock, formed just after the impact that formed the Moon, and it cooled and fell back as rain within about a thousand years.
The first atmosphere of the Earth was made of rock in the form of vapour. This vapour formed immediately after the collision that formed the Moon, then cooled and fell back as rain within about a thousand years. An atmosphere of steam replaced it. The steam contained all the water of the future ocean, and it exerted several hundred times the pressure of the air at the surface today. Beneath the steam, the molten surface took some two million years to solidify. Only then could the steam fall as rain and remain on the ground. The atmosphere that remained was almost pure carbon dioxide. Its pressure was of the order of a hundred atmospheres, that is, a hundred times the pressure of today's air. The young ocean below was near 230 °C, and only the weight of that atmosphere kept it liquid.
Why it matters
The ocean and the atmosphere both result from the cooling of the young Earth: the water condensed into the ocean, and the carbon dioxide stayed as gas. Neither the ocean nor the atmosphere has remained stable since. Every climate shown on this timeline is a later state of the atmosphere left by that cooling.
Dating & uncertainty
No sample of the first atmosphere survives. Researchers reconstruct it from models of a cooling magma ocean, a layer of molten rock at the surface, and from the gases still released by the mantle, the rock beneath. The open question is how fast the carbon dioxide was buried at sea in mineral form. If the burial was rapid, the planet became habitable ten to twenty million years after the impact. Miyazaki and Korenaga (2022) propose that a wet, chemically heterogeneous mantle could have removed the carbon dioxide, a greenhouse gas that retains heat, within 160 million years. Long afterwards, in the Archaean, a later eon, the atmosphere still contained ten to 2,500 times present-day carbon dioxide, according to Catling and Zahnle (2020).
Earth history as one day
00:28:3223 h 31 min before midnight
if Earth’s 4.54 billion years were compressed into a single day