Where does Earths water originally come from? Some of it was here when the earth was made (but locked into the rocks as hydrates ... much of that released as the Earth became molten.) And some came from comets and other ice particles that have bombarded the Earth since it was formed. No one knows which part was the major contributor. In more depth...: At some early point in time (after the moon) the Earth was a hot, glowing ball which would have out-gassed fairly completely. Hydrogen is light enough so that most of it would have escaped. Free Hydrogen is lost from a planet as small as Earth, it takes the outer gas giants with much stronger gravitational pulls to hold it Additionally, there was little or no oxygen (all the bound oxygen was in the rocks - which is mostly still there). One common theory of where the Earths water comes from was the comet impact theory. The belief was that earths water came from comets that impacted on the early Earth (recall that at this time there would be no atmosphere to disintegrate the comets). Scientists have looked at samples of ice from comets and the ratios of heavy water (water with an isotope of hydrogen called deuterium) does not match the water found in the oceans. This has lead scientist to believe the oceans are not made up of mostly cometary water. Evidence of water on the early Earth comes from Zircon Crystals dating from 4.53 billion years ago, only about 200 million years after the planet formed. Zircon crystals can only be created in the presence of water. This has lead scientist to believe that a large percentage of water was already in the rocks on Earth when it was created. However examination from fossil water taken from Hawaiian volcanoes that originally comes from the bottom layers of the crust also shows differences from modern water.
Posted on: Fri, 26 Sep 2014 01:38:24 +0000