11 Sep—Oceans

The Earth currently has approximately 344 million cubic miles of water, but early in the Earth's history, the solar wind had scoured most of the early Earth's water away, leaving the Earth rocky and barren. Some water trapped beneath the Earth's surface would have escaped into the atmosphere through volcanoes and outgassing, but not enough to explain the amount of water we have in our oceans today. Where did all the water that fills our oceans come from?

The early solar system was a wild place, full of roaming comets and asteroids that often crashed into their larger cousins, the planets. The leading theory about the origin of the oceans speculates that icy comets bombarded the Earth in its early history, bequeathing to us their water (and also their carbon dioxide, ammonia, nitrogen, and methane). The water we drink today may have come from as many as one million comets impacting the Earth billions of years ago.

At first, the Earth was too hot for the water be in a liquid state. Instead, it evaporated into the atmosphere, where it made up perhaps 80% of the early atmosphere. The rest of the atmosphere was still carbon dioxide and hydrogen sulfide, with small amounts of nitrogen and other gases.

The Earth may have had liquid water as early as 4,400 million years ago. The surface was much hotter then, but the heavy water vapor and carbon dioxide atmosphere created much more pressure than we experience today. The atmospheric pressure would have allowed liquid water to exist at high temperatures, perhaps twice the current boiling point of water.

Oceans—11 September

Anzu rent the sky with his talons,…
the flood came forth.…
The deluge belowed like a bull,
The wind resounded like a screaming eagle.
The darkness was dense, the sun was gone,…
the clamor of the deluge.
 —The Epic of Atrahasis

As the earth cooled about 4,200 million years ago, all that water that had been locked in the atmosphere as water vapor began to condense into liquid water and rain down on the surface of the Earth. There was so much water in the atmosphere that these torrential rains lasted for millions of years and filled up the oceans. (Maps of Time, p. 63)

As the oceans formed, the carbon dioxide in the atmosphere began to dissolve in the newly formed oceans. The greenhouse effect of the carbon dioxide which trapped heat lessened and the Earth began to cool off even further. The exodus of the water and carbon dioxide left behind an atmosphere of mostly nitrogen, more similar to our atmosphere today except that it lacked oxygen.