Privileged Planet: Lots of water (Introduction)

by David Turell , Wednesday, March 10, 2021, 14:25 (1142 days ago) @ David Turell

Perhaps covered with water 3-4 billion years ago:

https://www.sciencemag.org/news/2021/03/ancient-earth-was-water-world?utm_campaign=news...

"Earth’s total surface water was always assumed to be constant. Now, evidence is mounting that some 3 billion to 4 billion years ago, the planet’s oceans held nearly twice as much water—enough to submerge today’s continents above the peak of Mount Everest. The flood could have primed the engine of plate tectonics and made it more difficult for life to start on land.

"Rocks in today’s mantle, the thick layer of rock beneath the crust, are thought to sequester an ocean’s worth of water or more in their mineral structures. But early in Earth’s history, the mantle, warmed by radioactivity, was four times hotter. Recent work using hydraulic presses has shown that many minerals would be unable to hold as much hydrogen and oxygen at mantle temperatures and pressures. “That suggests the water must have been somewhere else,” says Junjie Dong, a graduate student in mineral physics at Harvard University who led a model, based on those lab experiments, that was published today in AGU Advances. “And the most likely reservoir is the surface.”

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"Two minerals found deep in the mantle store much of its water today: wadsleyite and ringwoodite, high-pressure variants of the volcanic mineral olivine. Rocks rich in those minerals make up 7% of the planet’s mass, and although only 2% of their weight is water today, “a little bit adds up to a lot,” says Steven Jacobsen, an experimental mineralogist at Northwestern University.

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"Although the larger ocean would have made it harder for the continents to stick their necks out, it could explain why they appear to have been on the move early in Earth’s history, says Rebecca Fischer, an experimental petrologist at Harvard and co-author on the AGU Advances study. Larger oceans could have helped kick off plate tectonics as water penetrated fractures and weakened the crust, creating subduction zones where one slab of crust slipped below another. And once a subducting slab began its dive, the dryer, inherently stronger mantle would have helped bend the slab, ensuring its plunge would continue, says Jun Korenaga, a geophysicist at Yale University. “If you cannot bend plates, you cannot have plate tectonics.”

"The evidence for larger oceans challenges scenarios for how life began on Earth, says Thomas Carell, a biochemist at Ludwig Maximilian University of Munich. Some researchers believe it began at nutrient-rich hydrothermal vents in the ocean, whereas others favor shallow ponds on dry land, which would have frequently evaporated, creating a concentrated bath of chemicals.

"A larger ocean exacerbates the biggest strike against the underwater scenario: that the ocean itself would have diluted any nascent biomolecules to insignificance. But by drowning most land, it also complicates the thin pond scenario. Carell, a pond advocate, says in light of the new paper, he is now considering a different birthplace for life: sheltered, watery pockets within oceanic rocks that broke the surface in volcanic seamounts. “Maybe we had little caves in which it all happened,” he says.

"The ancient water world is also a reminder of how conditional Earth’s evolution is. The planet was likely parched until water-rich asteroids bombarded it shortly after its birth. If the asteroids had deposited twice as much water or the present day mantle had less appetite for water, then the continents, so essential for the planet’s life and climate, would never have emerged. “It’s a very delicate system, the Earth,” Dong says. “Too much water, or too little, and it wouldn’t work.” " (my bolds)

Comment: Our Earth is very special. Contingency says natural forces were at work, but not if God managed the transformations.