When did oceans form on Earth? What evidence is preserved in the rock record?
Notes on origin of water: No water on earth at beginning. Probably, the oceans formed as soon as the Earth cooled enough for water to become liquid, about 4 billion years ago. The oldest sedimentary rocks are 3.9 billion years old (BA). These types of rocks require water to form – where did it come from? Some water and gasses came from this heating and reorganization of early earth. As surface cooled, water condensed to the liquid form. But, water has also been supplied since that time from the interior of earth. In the mantle, rocks are thought to be similar in composition to meteorites, which have 0.1 – 0.5 % water. Even though this doesn’t seem like much water, the mass of rocks in the interior is enough to fill the ocean 3 – 16 times, depending on how much water is in the mantle rocks. The water gets from the mantle to the surface from volcanic eruptions. Another estimate of how important this process could be comes from measuring how much water is in volcanic magma (such as comes
