Theoretical origin of life; Greenland earliest? (Introduction)

by David Turell , Thursday, November 22, 2018, 00:53 (1980 days ago) @ David Turell

Still debated:

https://www.livescience.com/64115-oldest-fossils-of-life-dispute.html?utm_source=ls-new...

"Scientists will gather in a remote and snowy part of southwestern Greenland next summer to try to determine if rocks from 3.7 billion years ago contain some of the oldest fossils of life on Earth.

"Tiny, triangular structures found in these rocks have been a source of controversy, with some scientists now saying they are not evidence of early life on Earth. The scientists who first reported that they were fossilized evidence of life are defending their claims.

"In a paper published online Oct. 17 in the journal Nature, planetary scientist Abigail Allwood and colleagues, who examined the ancient rocks in Greenland, reported that purely geological processes could explain the triangular rock formations — and that while they might still be formed by microbial life, there was not enough evidence to show definitely that they were.

"Allwood, who works for NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, is the principal investigator building an instrument called PIXL, based on x-ray fluorescence of rock samples, which will be used by the Mars 2020 rover to search for fossilized evidence of life in Martian rocks.

"Allwood’s team used the PIXL instrument to test rock samples from Greenland and reported that concentrations of titanium, potassium, and carbonate chemicals in the rocks did not show that the triangular structures had been formed by microbial life. [The 7 Most Mars-Like Places on Earth]

"Scientists think that about 3.7 billion years ago, the environment on Mars was very similar to the environment on Earth at that time, and that early forms of life might have evolved at the same time on both planets — although the very cold and dry Martian environment is now thought to be lifeless.

"The Isua Greenstone Belt in southwestern Greenlandis thought by geologists to contain some of the oldest exposed rocks on Earth. Until recently, much of the area was covered by snow — only in the last few years has the snow melted enough for scientists to examine many of the rocks.

"In 2016, geochemist Allen Nutman of Wollongong University in Australia and his colleagues reported in a paper published in the journal Nature that triangular structures seen on the surface of some of the Isua rocks were cross-sections of cone-shaped stromatolites — tiny, fossilized structures built by microbial colonies on the floors of bodies of water.

"Nutman told Live Science in August 2016 that the concentrations of titanium and potassium inside the triangular structures were different than in the rock outside the structures — a possible chemical “biosignature”. His team also reported that the concentrations of carbonate chemicals suggested the microbial colonies were drawing carbonates out of the surrounding seawater.

"Until the discovery in Greenland, the earliest known stromatolites had been found at Strelley Pool in the Pilbara region of Western Australia and dated to about 3.4 billion years ago. Nutman's find, if verified, would push back the earliest evidence for the appearance of life on Earth by about 300,000 years.

"Allwood visited the same rocks in the Isua region of Greenland this summer and took samples for laboratory testing with the PIXL instrument, which will be attached to the rover to carry out X-ray fluorescence analysis on rock on Mars.

"She said that after examining the rocks and studying the geochemistry of the rock samples, she did not believe that the triangular structures were fossilized evidence of very early microbial life: "I think the evidence is very much not in favor of that interpretation," she said.

"As well as finding that the supposedly conical structures actually formed long triangular ridges within the rock, Allwood said that the geochemistry of the structures was the same as in some other patches of weathered rock nearby that did not appear to contain any stromatolites.

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"Because Allwood and her colleague had analyzed different rock samples than the ones his team had analyzed, they had inevitably found that their observations did not exactly match those of his team. "This is a classic comparing apples and oranges scenario," he wrote.

"Nutman said that his team had found the structures could not be purely geological in origin, and that their shape and geochemistry indicated they were created by "extremely rare stromatolites in the Isua rocks, preserved in a tiny relict of a 3,700-million-year-old shallow sea environment."

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"The dispute over the Greenland rocks means that the oldest established fossils of life on Earth may again be the stromatolites found at Strelley Pool in Western Australia.

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"Another recent study has suggested that an outcropping of primitive ocean crust in Quebec in Canada could contain fossils that are even older — between 3.77 billion and 4.29 billion years old — but that study also needs more scientific scrutiny, Allwood said."

Comment: Whatever the exact time for life to appear, it is amazing that it developed so soon after Earth's formation