After decades of telling the public comets brought Earth’s water, scientists are giving up on the idea. It was volcanoes, now they say.
A geologist and mineralogist from Trinity College Dublin says that “Scientists are changing their minds about how the Earth’s water got here.” Writing on The Conversation, Balz Kamber points to evidences that go against the special-delivery theory (what we have called the “water balloon theory”, 7/23/12) for the origin of Earth’s water.
- The isotope of ruthenium found on Earth’s surface is the wrong type to have come from the outer solar system. Ruthenium, a siderophile (iron-loving) element, should have been dragged with iron into Earth’s core. This suggested to geophysicists in the 1970s that it was delivered by comets and asteroids in a “late veneer” after the Earth differentiated, leaving water on the surface as a by-product. But if the impactors were from the inner solar system, they would have been too dry.
- Zircons, thought to have been formed 4.3 billion years ago, appear to have been in contact with water some 200– to 400-million Darwin Years before the “late veneer” should have formed.
- The heat of impacts may have obliterated water as much as delivered it.
- The presence of chlorine implies that it had water to dissolve into – otherwise it would have been lost to space.
If water was on Earth early on, it must have already been here at the time of formation. How could that be on a molten world rife with volcanoes? According to Kamber, volcanoes were the answer. They spewed up minerals that contained hydroxyl ions (OH–) which recombined into H2O as the minerals crystallized. Cute theory; does it work?
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