Science

Diverse microfossils suggest extraterrestrial life should be widespread

Diverse microfossils suggest e...
A sliver of 3.5 billion-year-old rock, being studied on the SIMS instrument
A sliver of 3.5 billion-year-old rock, being studied on the SIMS instrument
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One of the microfossils found in Western Australia, dating back 3.5 billion years
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One of the microfossils found in Western Australia, dating back 3.5 billion years
Carbon isotope analysis revealed that this 3.5 billion-year-old micro-organism likely consumed methane
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Carbon isotope analysis revealed that this 3.5 billion-year-old micro-organism likely consumed methane
An example of one of the microfossils
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An example of one of the microfossils
A sample of 3.5 billion-year-old rock, after it has been studied with the SIMS instrument
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A sample of 3.5 billion-year-old rock, after it has been studied with the SIMS instrument
A UW-Madison field trip to the Western Australian dig site in 2010, where the microfossils were found
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A UW-Madison field trip to the Western Australian dig site in 2010, where the microfossils were found
John Valley (left) and Kouki Kitajima (right), who worked on the study
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John Valley (left) and Kouki Kitajima (right), who worked on the study
A sliver of 3.5 billion-year-old rock, being studied on the SIMS instrument
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A sliver of 3.5 billion-year-old rock, being studied on the SIMS instrument
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The early years of Earth are a murky mess, so we don't really know how or when life first arose. With each new fossil discovery, the timeline for life is pushed back earlier and earlier, but the really old ones are usually up for debate. That was the case for microscopic fossils found in Western Australia decades ago, which appeared to show evidence of life dating back almost 3.5 billion years, but those findings have since been contested. New analysis shows that the microfossils are indeed biological, and the find may have implications for the likelihood of extraterrestrial life.

The title of Oldest Fossil is a controversial one. This new study, from scientists at UCLA and the University of Wisconsin-Madison, lays claim to it with these microfossils dating back 3.465 billion years. That's pretty old, but it's just pipped by fossils found in an ancient hot spring in the Pilbara region of northwestern Australia, which are 3.48 billion years old. Both are beaten out by stromatolites in Greenland that have been dated to 3.7 billion years, while a batch of Canadian fossils may have celebrated a staggering 4.3 billion birthdays.

But because it's so difficult to peer that far back in time, all of these finds need to be taken with a grain of salt. The fossils at the heart of this study were first described in 1993, but it was later debated whether or not they were biological or if the microscopic structures could have formed through other processes. On closer analysis, the team now claims to have confirmed that the fossils are indeed biological, identified different taxa that they belong to and described the possible physiological behaviors of the organisms.

An example of one of the microfossils
An example of one of the microfossils

The team analyzed the samples using a secondary ion mass spectrometer (SIMS). This instrument can identify the different carbon signatures of organisms by weighing up the ratio of carbon-12 to carbon-13 isotopes. By comparing those ratios to a standard figure, as well as a sample of neighboring rock that contained no fossils, the team was able to confirm that the fossils were indeed of biological origin.

"The differences in carbon isotope ratios correlate with their shapes," says John Valley, co-lead researcher on the study. "If they're not biological there is no reason for such a correlation. Their C-13-to-C-12 ratios are characteristic of biology and metabolic function."

Based on this finding, the team identified 11 specimens of organisms that belonged to five different taxa, and determined how they might have lived. Among them were phototropic bacteria that produce energy from sunlight, Archaea that produce methane, and gammaproteobacteria that consume methane. At that time in Earth's history, methane is believed to have been the main constituent of the Earth's atmosphere.

Carbon isotope analysis revealed that this 3.5 billion-year-old micro-organism likely consumed methane
Carbon isotope analysis revealed that this 3.5 billion-year-old micro-organism likely consumed methane

Discovering life this diverse at this early stage has important implications for the hunt for extraterrestrial life. If life can evolve so quickly in Earth's history, the team reasons, then it should be able to do so on other planets just as easily.

"By 3.465 billion years ago, life was already diverse on Earth; that's clear – primitive photosynthesizers, methane producers, methane users," says J. William Schopf, lead author of the study. "These are the first data that show the very diverse organisms at that time in Earth's history, and our previous research has shown that there were sulfur users 3.4 billion years ago as well. If the conditions are right, it looks like life in the universe should be widespread."

NASA is currently planning to collect a sample of Martian soil and return it to Earth to study, and the team suggests that the SIMS instrument will probably be used to check if similar microfossils exist on the Red Planet.

The research was published in the journal PNAS.

Sources: UCLA, University of Wisconsin-Madison

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3 comments
piperTom
"By 3.465 billion years ago, life was already diverse on Earth..." That is good news and it does imply that we'll find life wherever Earth-like conditions prevail. Of course, the conditions have to be stable for about a billion years, but astronomers can guess at that, too. Now, the bad news. From diverse life to intelligent life took another 3.4+ billion years. That huge gap argues that the step up to intelligence is very difficult. The galaxy may well be teeming with life and we are still alone.
matt43
This is hilarious... these people dating rocks to "3.456 billion years". Based on the most absurd and flimsy of presuppositions, they come up with the most ridiculous crap possible.
News flash people, the Earth hasn't been around for 3.456 billion years. Nor million. All the (real) scientific evidence is very explicit in dating the Earth to less than 10,000 years, but hey, heaven forbid you acknowledge that truth, it might change your idiotic presuppositions and make you accountable to someone you hate.
highlandboy
The fossils can be shown to be biological since the C12/C13 ratios differ from the surrounding rock. This is reproducible in plants that photosynthesise using 2 different mechanisms either C3 or C4. I’m not sure about what mechanisms methane producing or absorbing bacteria use that differentiate the levels of C12/C13.
As for the dating, who knows what method was used. The article gives no basis for the dates and therefore is not open to scientific scrutiny and is therefore very poor science.
As for any links to extra-earth occurance, they are pure imagination. We are yet to find any item from outside earth with biological origins.
This article is therefore interesting in the same way as science fiction is interesting, but hardly justifies its title.