We don’t entirely know when life arose on Earth, but there’s increasing evidence that it happened pretty quickly after the planet itself got started. Now, scientists have found some of the earliest direct evidence, in the form of preserved organic remains in 3.5-billion-year-old stromatolites in Australia.

In the Pilbara region of Western Australia sits the Dresser Formation, an expansive series of stromatolites. These rocky formations are usually believed to represent some of the oldest evidence of life, created layer by layer as generations of ancient microorganisms lived and died there.

There had never been direct evidence that this was the case, but now researchers at the University of New South Wales (UNSW) may have found the “smoking gun” that scientists have been hunting for decades.

The problem, according to the researchers, is that samples are usually taken from the surface of the rock, where they’re subject to weathering. To get around that, the team instead drilled down to get samples from deep within the rock, where traces of ancient life are more likely to have been preserved.

These cores were then examined using several techniques, such as high-powered electron microscopy, spectroscopy and isotope analysis. The stromatolites were found to be mostly made up of pyrite, but with clear signs of organic matter.

“This is an exciting discovery – for the first time, we’re able to show the world that these stromatolites are definitive evidence for the earliest life on Earth,” says Raphael Baumgartner, lead researcher of the study. “The organic matter that we found preserved within pyrite of the stromatolites is exciting – we’re looking at exceptionally preserved coherent filaments and strands that are typically remains of microbial biofilms.”

At 3.5 billion years old, the team says that this discovery marks some of the oldest direct evidence of life on Earth. The same Dresser Formation previously revealed that life moved out of the ocean into hot springs not long after this, about 3.48 billion years ago. But these aren’t the oldest themselves – the earliest concrete evidence belongs to stromatolites found in Greenland, which date back 3.7 billion years. Other fossils in Canada could date back as far as 4.3 billion years, but these are still contentious.

The research was published in the journal Geology.

Source: UNSW