Scientists uncover 3.22 billion year old microbes in South Africa that push back estimates of when terrestrial life started on Earth by 500 million years

• Scientists believe life started in the oceans on Earth around 3.5 billion years ago
• Until now, it was thought that terrestrial life didn't begin until 2.7 billion years ago
• The latest research is the 'oldest and least unambiguous work' that life also existed on land more than three billion years ago 

Scientists have discovered the earliest definitive signs of terrestrial life on Earth.

The fossilised remains of microbial life, which dates back 3.22 billion years, were found on the Barberton Greenstone Belt, in South Africa.

Until now, experts believed primitive organisms moved from the oceans, which covered the majority of the planet at that time, to the world's first supercontinent around 2.7 billion years ago.

However, the latest evidence pushes back these estimates by 500 million years. 

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Three billion years ago, Earth was a waterworld with an atmosphere rich in methane.

As a result, bacteria that fed on oxygen accumulated close to microscopic vents found on the ocean floor. When land started to emerge, sections of the seabed was forced up towards the surface.

The first supercontinent, Kenorland, was not fully formed until 2.7 billion years ago and experts previously believed the first microbes to live on land were dated back to this time.

Examples of terrestrial organisms dating back 2.7 billion years were found in a different location on the Barberton Greenstone Belt in South Africa, according to The Scientist.

However, a study last year suggested microbes found on a 3.5 billion year old volcano in the Pilbara region of Western Australia may have also have lived on land.

The evidence included well-preserved bubbles trapped in a sticky microbial fluid and layers of rock formed by ancient microorganisms. 

However, these findings were not conclusive.

Now scientists led by Martin Homann from the European Institute for Marine Studies have discovered the first definitive evidence of ancient terrestrial life.

'This work represents the oldest and least unambiguous work that we have so far that life existed on land already 3.2 billion years ago,' Kurt Konhauser, a professor of earth and atmospheric sciences at the University of Alberta in Canada, who was not involved in the research, told The Scientist.

'The colonisation of emergent continental landmass by microbial life was an evolutionary step of paramount importance in Earth history,' researchers wrote in the paper published in Nature Geoscience.

'Here we report direct fossil evidence for life on land 3,220 million years ago (Ma) in the form of terrestrial microbial mats draping fluvial conglomerates and gravelly sandstones of the Moodies Group, South Africa,' they added.

Scientists looked at ancient sedimentary rocks which have imprints of bacteria and archaea called 'fossilised microbial mats'.

They believe this sedimentary rock was once part of an ancient river delta. 

Researchers came to this conclusion by analysing the organic carbon and nitrogen isotopes within the samples. These were distinctly different from marine samples, suggesting the microbes had developed different metabolisms to live on land.

'The structures and isotopic composition of the microbial mats certainly seem to suggest the presence of photosynthetic microbes already existing on land,' said Dr Konhauser.