COE - The Hydrosphere Lesson

 

The Hydrosphere

Earth is the only planet whose temperature range allows all three phases of water to exist on its surface. But what was the source of this water? For decades, the debate has focused on two possible explanations:

The first theory focused on the comets that periodically enter our solar system. Comets are essentially giant dirty chunks of ice, so it was theorized that multiple impacts by comets during Earth's early history brought water to the surface.

The competing theory focused on volcanoes, which release a variety of gases into the atmosphere in addition to lava and ash. Water vapor is one of these gases, so the competing theory was that water was present during the formation of the planets, and became incorporated into the planets during accretion. Volcanic eruptions allowed the water trapped inside the Earth to be released into the atmosphere, where it cooled and rained back down onto the Earth's surface.

Recent scientific discoveries present evidence that favors the outgassing theory over the comet theory, although comets haven't been ruled out entirely.

Regardless of the source, the water cycle brought rain upon the barren rocks over and over, dissolving minerals and carrying them down via rivers to the oceans. Over time, these ions would combine to form the salts that differentiate marine environments from freshwater.

 

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