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takyon writes:

http://newsroom.unsw.edu.au/news/science-tech/oldest-evidence-life-land-found-348-billion-year-old-australian-rocks

Fossils discovered by UNSW scientists in 3.48 billion year old hot spring deposits in the Pilbara region of Western Australia have pushed back by 580 million years the earliest known existence of microbial life on land. Previously, the world's oldest evidence for microbial life on land came from 2.7- 2.9 billion-year-old deposits in South Africa containing organic matter-rich ancient soils.

"Our exciting findings don't just extend back the record of life living in hot springs by 3 billion years, they indicate that life was inhabiting the land much earlier than previously thought, by up to about 580 million years," says study first author, UNSW PhD candidate, Tara Djokic. "This may have implications for an origin of life in freshwater hot springs on land, rather than the more widely discussed idea that life developed in the ocean and adapted to land later."

Scientists are considering two hypotheses regarding the origin of life. Either that it began in deep sea hydrothermal vents, or alternatively that it began on land in a version of Charles Darwin's "warm little pond". "The discovery of potential biological signatures in these ancient hot springs in Western Australia provides a geological perspective that may lend weight to a land-based origin of life," says Ms Djokic.

Earliest signs of life on land preserved in ca. 3.5 Ga hot spring deposits (open, DOI: 10.1038/ncomms15263) (DX)

Previously:
3.7 Billion-Year-Old Fossil Found
Oldest Evidence of Life on Earth Found in 3.77-4.28 Billion Year Old Fossils
Researchers Use Genetic Analysis to Determine That Comb Jellies Were the Earliest Animals

Original Submission

takyon writes:

According to a new fossil analysis, previously described Australian fossils do contain evidence of 3.5-billion-year-old microbial life. However, the complexity of the fossilized microbes suggests that life arose much earlier, possibly as far back as 4 billion years ago:

In 1992, researchers discovered evidence of what was then potentially the earliest life on Earth: 3.5-billion-year-old microscopic squiggles encased in Australian rocks. Since then, however, scientists have debated whether these imprints truly represent ancient microorganisms, and even if they do, whether they're really that old. Now, a comprehensive analysis of these microfossils suggests that these formations do indeed represent ancient microbes, ones potentially so complex that life on our planet must have originated some 500 million years earlier.

The new work indicates these early microorganisms were surprisingly sophisticated, capable of photosynthesis and of using other chemical processes to get energy, says Birger Rasmussen, a geobiologist at Curtin University in Perth, Australia, who was not involved with the work. The study "will probably touch off a flurry of new research into these rocks as other researchers look for data that either support or disprove this new assertion," adds Alison Olcott Marshall, a geobiologist at the University of Kansas in Lawrence who was not involved in the effort.

[...] The analysis detected several distinct carbon ratios in the material [DOI: 10.1073/pnas.1718063115] [DX], Schopf, Valley, and colleagues report today in the Proceedings of the National Academy of Sciences. Two types of microfossils had the same carbon ratio as modern bacteria that use light to make carbon compounds that fuel their activities—a primitive photosynthesis that did not involve oxygen. Two other types of microfossils had the same carbon ratios as microbes known as archaea that depend on methane as their energy source—and that played a pivotal role in the development of multicellular life. The ratio of a final type of microfossil indicated that this organism produced methane as part of its metabolism.

That there are so many different carbon ratios strengthens the case that these are real fossils, Schopf says. Any inorganic processes that could have created the squiggles would be expected to leave a uniform carbon ratio signature, he says. The fact that microbes were already so diverse at this point in Earth's history also suggests that life on our planet may date back to 4 billion years ago, he says. Other researchers have found signs of life dating back at least that far, but those findings are even more controversial than Schopf's.

Also at University of Wisconsin-Madison.

Previously: Ancient Rocks Record First Evidence for Photosynthesis That Made Oxygen
3.7 Billion-Year-Old Fossil Found
Oldest Evidence of Life on Earth Found in 3.77-4.28 Billion Year Old Fossils
Earliest Known Evidence for Microbial Life on Land: 3.48 Billion Years Old

Original Submission

takyon writes:

Geologists Question 'Evidence Of Ancient Life' In 3.7 Billion-Year-Old Rocks

The oldest evidence of life on Earth probably isn't found in some 3.7 billion-year-old rocks found in Greenland, despite what a group of scientists claimed [DOI: 10.1038/nature19355] [DX] a couple of years ago. That's according to a new analysis [DOI: 10.1038/s41586-018-0610-4] [DX], published Wednesday in the journal Nature by a different team of experts. This second group examined structures within the rock that were thought in 2016 to have been produced by communities of single-celled microbes that grew up from the bottom of a shallow, salty sea. A three-dimensional look at these structures shows that instead of having a telltale upside-down ice-cream cone shape — the kind produced by microorganisms — they are shaped like a Toblerone candy bar.

"They're stretched-out ridges that extend deeply into the rock," said Joel Hurowitz, a geochemist at Stony Brook University in New York and an author of Wednesday's paper. "That shape is hard to explain as a biological structure and much easier to explain as something that resulted from rocks being squeezed and deformed under tectonic pressures." Asked what the chances were that the structures were created by ancient microbes, astrobiologist Abigail Allwood — of NASA's Jet Propulsion Laboratory and lead author of this second analysis — said: "I don't think there's much chance at all."

[...] All of this is vigorously disputed by the researchers who originally claimed that the Greenland rocks contained the world's oldest fossils. They stand by that claim and say that Allwood and her colleagues based their work on just a cursory, one-day visit to the site. [...] Vickie Bennett, of the Australian National University, added that she found the new study "disappointing" and "unfortunate" in that it "only serves to confuse" the earlier research that she and her colleagues did on these ancient rocks. "Basically they did not look at the same rocks — and the details matter," Bennett told NPR in an email. In her view, the rocks in the current study are a "poor-cousin equivalent to the rocks of our original study" and the new analysis "was not conducted with care."

The article does not address evidence found in Quebec in 2017, dated to between 3.77 and 4.28 billion years ago.

Also at USA Today.

Previously: 3.7 Billion-Year-Old Fossil Found
Earliest Known Evidence for Microbial Life on Land: 3.48 Billion Years Old
Analysis of Microfossils Finds that Microbial Life Existed at Least 3.5 Billion Years Ago - "However, the complexity of the fossilized microbes suggests that life arose much earlier, possibly as far back as 4 billion years ago."

Original Submission