Remnants of life in ancient rocks reveal Earth had a rich ecosystem 3.4 billion years ago

• Scientists have managed to extract evidence from an ancient fossil of early life on Earth.
• Rock in South Africa is thought to contain some of the oldest known fossils in the world.

Earth may have been teeming with a complex ecosystem of microorganisms as far back as 3.4 billion years ago.

Scientists, led by the University of Göttingen in Germany, studied fossils taken from the Buck Reef Chert in the Barberton Greenstone Belt in South Africa.

The area is known for having well-preserved ancient sedimentary rocks close to its surface, which can provide a snapshot of our planet's history.

In some of these rocks, researchers found chemical signatures that provided an insight into the biodiversity of ancient organisms, adding evidence to the early beginning of life on our planet.

"What I'm reading out of this is that early life was working very much similarly to life today," Frances Westall, an expert in ancient biology from the French National Centre for Scientific Research, who was not involved in the study, told New Scientist.

Life on Earth more than 3 billion years ago

Scientists think that life on Earth began around 4.3 billion years ago, but tracking down evidence dating back to that time is a difficult task.

Still, by drilling straight into ancient rock, scientists have found peculiar, carbon-rich layers in several cores taken from around the world.

These layers are widely thought to be fossilized life, frozen in rock billions of years ago.

The oldest accepted rock core containing fossilized life was found in Pilbara, Australia. This is thought to be more than 3.5 million years old.

Older carbon-rich layers have been uncovered, but because of their age, it's not possible to know for sure that these are fossils or another non-biological process.

So scientists have been racing to understand all they can from these ancient fossils. And what they've found is that Earth was already teaming with life more than three billion years ago.

"It's very difficult to see the trend, simply because of a lack of well-preserved rocks," says Westall.

"Personally, I think life emerged on Earth during the Hadean, probably about 4.2, 4.1 billion years [ago]," Westall said referring to a period of time that ended about four billion years ago.

Microbes' metabolisms, billions of years after they died

The samples from the Barberton Greenstone Belt are among the oldest known fossils of life — dating back to about 3.42 billion years ago.

Earlier analyses had looked at the shape of the fossilized microbes in the rock, suggesting these were varied and probably lived near water.

The new analysis, published in the peer-reviewed journal Precambrian Research on January 12, pushed the analysis even further by looking at the chemicals that made up the microbes.

Their study showed that, as expected, there were a lot of "photoautotrophs" back then, meaning the bacteria were able to take sunlight and turn it into energy, much like some bacteria that exist today.

But they also found evidence that some microbes were likely already able to use up sulfate and make complex chemicals like methane and acetate.

This reinforces the idea that life was already very complex 3.4 billion years ago, capable of using up carbon in a variety of ways that we still see today, the scientists said in the study.

"These results highlight the existence of an advanced biological carbon cycle as early as 3.42 Ga ago," they said.