A new study shows that iron-bearing rocks that formed at the ocean floor 3.2 billion years ago carry unmistakable evidence of oxygen. The only logical source for that oxygen is the earliest known example of photosynthesis by living organisms, say University of Wisconsin-Madison geoscientists.
"Rock from 3.4 billion years ago showed that the ocean contained basically no free oxygen," says Clark Johnson, professor of geoscience at UW-Madison and a member of the NASA Astrobiology Institute. "Recent work has shown a small rise in oxygen at 3 billion years. The rocks we studied are 3.23 billion years old, and quite well preserved, and we believe they show definite signs for oxygen in the oceans much earlier than previous discoveries."
The most reasonable candidate for liberating the oxygen found in the iron oxide is cyanobacteria, primitive photosynthetic organisms that lived in the ancient ocean. The earliest evidence for life now dates back 3.5 billion years, so oxygenic photosynthesis could have evolved relatively soon after life itself.
Until recently, the conventional wisdom in geology held that oxygen was rare until the "great oxygenation event," 2.4 to 2.2 billion years ago.
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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
(Score: -1, Offtopic) by Anonymous Coward on Thursday October 08 2015, @03:51PM
Imagine all the creationists (ID is creationism) who have to miss this very interesting and awesome part of our reality, just because it contradicts their bronze-age book. A whole world (literally and figuratively) of insight, amazement, bewilderment, coolness and knowledge that can never be part of their reality because of superstition.
Sad, so sad...
But on the other hand, this finding is cool... !
(Score: 1, Insightful) by Anonymous Coward on Thursday October 08 2015, @07:46PM
This is not insightful. This is trolling.
(Score: -1, Troll) by Anonymous Coward on Thursday October 08 2015, @08:58PM
The only reason you could call this trolling is because you take issue with the term "bronze age book"... which is factually correct.
(Score: 3, Interesting) by kurenai.tsubasa on Thursday October 08 2015, @11:11PM
It's partially correct. Other books and documents in the collection known as the Bible are iron age [wikipedia.org], although the hero story archetype [wikipedia.org] upon which the story of Jesus is based is very likely bronze age in origin.
(Score: 3, Insightful) by inertnet on Thursday October 08 2015, @10:50PM
Nobody said it better than Christopher Hitchens: https://www.youtube.com/watch?v=JXEiKPxCSdA [youtube.com]
(Score: 0) by Anonymous Coward on Thursday October 08 2015, @04:29PM
Pretty soon it adds up to a really long time.
(Score: 3, Insightful) by khallow on Thursday October 08 2015, @11:48PM
Until recently, the conventional wisdom in geology held that oxygen was rare until the "great oxygenation event," 2.4 to 2.2 billion years ago.
Sounds like the conventional wisdom still holds. One of the things that strikes me here is that this has implications for terraforming. If it took nature a billion years to terraform Earth, it may take us longer than a few centuries to do the same to another world, like Mars or Venus for example, due to the need to get the ground in chemical equilibrium with the atmosphere.
(Score: 2) by bzipitidoo on Friday October 09 2015, @01:02AM
I have read that if the Earth's atmosphere were somehow reset to the way it was about 4 billion years ago, mostly nitrogen and CO2 and no free oxygen, it would take about 1500 years for bacteria and plants to raise the level of free oxygen to the current amount of 21%. Of course animals would all suffocate. Seems early life was comparatively weak, lacking numbers and all kinds of evolutionary advances.
I have pieced together a timeline of significant events in the History of the Earth. The article is, as is all too typical, a little sensational. 3.5 bya (billion years ago) is the earliest probable fossils, of cyanobacteria, and 3.46 bya is the earliest known certain fossils. We also have evidence to 3.7 bya of banded iron formations, rusted iron, which most likely was caused by free oxygen released by life. Even earlier, at 3.8 bya, are lipids which are biomarkers for life. While the lipids could conceivably have been created by non-biological processes, it's highly unlikely. More indirect evidence, of an enrichment in C12, dates to 3.85 bya.