Privileged Planet: why does Earth have so much water? (Introduction)

by David Turell , Monday, November 05, 2018, 20:00 (1998 days ago) @ David Turell

Water is vital for life to exist and we have lots of water. The issue is not settled as to how it happened here , but this research indicates most of it appeared early in Earth formation, before the impact that theoretically created the moon, and theoretically from ice containing meteorites and asteroids impacting the early Earth body:

https://www.geologypage.com/2018/04/water-appeared-while-earth-was-still-growing.html

"Up until about ten years ago, scientists thought they had a pretty good picture of how the moon and Earth came to co-exist. Then more precise measurements blew it all wide open, and scientists are still struggling to reconcile them.

"As part of that effort, a team including UChicago cosmochemist Nicolas Dauphas performed the largest study to date of oxygen isotopes in lunar rocks, and found a small but measurable difference in the makeup of the moon and Earth.

"Published March 28 in Science Advances, the research proposes that Earth acquired the majority of its water during the main stage of its growth — which counters a popular theory.

"The most widely accepted theory of the origin of the Moon speculates that a giant object smashed into the proto-Earth at just enough velocity that part of both bodies broke off and formed the moon. The Earth has a little of the moon and the moon has more of the Earth, but they’d be mostly different objects. Early measurements — many taken by the late UChicago geochemist Robert Clayton — did not have sufficient precision to tell the Moon and Earth apart.

"But in the last decade, Dauphas said, it became clear this picture wasn’t quite right. Elements can come in different forms, called isotopes, and these give scientists clues to the rock’s origin. As ways to measure isotopes improved, scientists discovered striking similarities between the moon and the Earth. Referred to as the “lunar isotopic crisis,” this was a problem for the main theory of lunar formation, because it’s highly unlikely the isotopes would be exactly the same for two random objects in the solar system.

***

"Seeking to clarify the issue, the researchers measured the oxygen isotopes of both lunar and terrestrial rocks with extremely high precision. They found a very small, but detectable difference between the isotopes between the two bodies.

***

"Their model suggests that only 5 percent to 30 percent of all the water on Earth would have arrived on meteorites after the great impact."

Comment: Here is a segment of discussion from the original article:

http://oro.open.ac.uk/54309/1/Greenwood%20et%20al%202018.full.pdf

"A late veneer explanation for the 3 to 4 ppm D17O Earth-Moon
difference implies that a large fraction of Earth’s water was delivered
earlier than the giant impact event. Terrestrial hydration would have
been synchronous with the main phase of Earth’s accretion and not
the result of a late-stage delivery of water from the outer solar system
(36). Fortuitously for the evolution of life on our planet, despite the
high energy of the Moon-forming event, Earth retained enough of its
primordial water to remain a habitable environment. These findings
are consistent with modeling studies, which indicate that Earth would
have had an ocean before the era of giant impacts and that this ocean
was retained despite the high energy of this terminal accretion phase."

What this implies to me is a special handling of the Earth to create the enormous volumes of water we have in our oceans and the large subterranean deposits (ocean-sized) recently discovered all of which are vital to the support of life. It is known frozen water is present all over the universe, and some how lots of it is concentrated here in this privileged planet.