Earth & Conservation

3.5-Billion-Year-Old Fossils May Be the Oldest on Earth

The conclusion, made by researchers at the University of Wisconsin-Madison and UCLA, suggests that extraterrestrial life might develop more easily than thought.

An epoxy mount containing a sliver of a nearly 3.5 billion-year-old rock from the Apex chert deposit in Western Australia is pictured at the Wisconsin Secondary Ion Mass Spectrometer Lab in Weeks Hall. | Jeff Miller
An epoxy mount containing a sliver of a nearly 3.5 billion-year-old rock from the Apex chert deposit in Western Australia is pictured at the Wisconsin Secondary Ion Mass Spectrometer Lab in Weeks Hall. | Jeff Miller

How common is life in the universe? This is a hard question for scientists to answer definitively, since we only have one data point: Earth.

But a new study published in the Proceedings of the National Academy of Sciences on some of Earth’s oldest fossils has shown that a diverse group of organisms had already evolved on our planet nearly 3.5 billion years ago, much earlier in Earth’s history than thought. The researchers say the new findings mean it might be easy for life to develop and evolve, which would increase the likelihood that life is widespread throughout the universe.

“By 3.465 billion years ago, life was already diverse on Earth; that’s clear,” J. William Schopf from UCLA, lead author of the new study, said in a statement. “This tells us life had to have begun substantially earlier and it confirms that it was not difficult for primitive life to form and to evolve into more advanced microorganisms.”

Schopf added that the research shows, if the conditions are right, “it looks like life in the universe should be widespread.”

The new study looked at fossilized microorganisms that were found in Western Australia in 1992. Schopf has been studying these fossils since their discovery and has published several papers about them, determining their age at 3.465 billion years. In previous research, Schopf and his colleagues established that the origin of the fossils was biological, which was somewhat controversial. Some critics argued that the oddly shaped cylindrical fossils were just odd minerals that only look like biological specimens. However, subsequent research in 2002 confirmed the fossils’ biological nature.

Research published in the journal Nature found that the remains of iron-eating bacteria dated back to between 3.8 billion and 4.3 billion years ago. 

An example of one of the microfossils discovered in a sample of rock recovered from the Apex Chert. A new study used sophisticated chemical analysis to confirm the microscopic structures found in the rock are biological. | J. William Schopf

Schopf wanted to understand what kind of microbial organisms these fossils are and if they were advanced or primitive.

Schopf teamed up with John Valley, a geoscience professor from the University of Wisconsin-Madison who has been working for 10 years to refine a technique called secondary ion mass spectroscopy, or SIMS. This device shoots an ion beam on a surface and, in a vacuum, collects and analyzes ejected secondary ions, searching for specific types of isotopes. 

The work was painstaking, as the fossils are each only about 10 micrometers wide, meaning eight of them could fit along the width of a human hair.

The team analyzed eleven microfossils and were able to separate the carbon from each fossil into its constituent isotopes and measure their ratios. The results indicated they were “characteristic of biology and metabolic function,” Valley said in a statement.

They found several different types of organisms — “a primitive but diverse group,” Schopf said. Two of the species appeared to have performed a simple form of photosynthesis, another apparently produced methane gas, and two others appear to have consumed methane and used it to build their cell walls. 

In short, these fossils represent a “community” that lived together and “were a significant component of Earth’s early biosphere,” the team wrote, and were comprised of primitive photosynthesizers, methane producers, and methane users.

Geoscience professor John Valley, left, and research scientist Kouki Kitajima collaborate in the Wisconsin Secondary Ion Mass Spectrometer Lab in Weeks Hall.

They found several different types of organisms — “a primitive but diverse group,” Schopf said. Two of the species appeared to have performed a simple form of photosynthesis, another apparently produced methane gas, and two others appear to have consumed methane and used it to build their cell walls. 

In short, these fossils represent a “community” that lived together and “were a significant component of Earth’s early biosphere,” the team wrote, and were comprised of primitive photosynthesizers, methane producers, and methane users.

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Because several different types of microbes were shown to be already present by 3.5 billion years ago, this means life started much earlier than that. Earlier studies by Valley have shown that liquid water oceans existed on Earth as early as 4.3 billion years ago, more than 800 million years before the

Western Australian fossils studied in this research would have been alive, and just 250 million years after Earth formed.

The team said this new study strengthens the case for life existing elsewhere in the universe because it would be extremely unlikely that it arose quickly on Earth but did not develop anywhere else.

“This is something we all would like to find out,” Valley said. 

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