Fossilised Filaments from Hot Ocean Vent Claimed to Be Earliest Evidence of Life on Earth

Iron oxide tubes may be oldest microfossils and evidence of life on Earth, study suggests. (Supplied: Matthew Dodd)

Tiny mineralised filaments smaller than a human hair found in rocks more than 3.77 billion years old may be evidence of one of the oldest lifeforms on Earth.

An international team of scientists has discovered what they believe are the fossilised remains of microorganisms that would have clustered around a hot, seafloor vent.

They said the discovery, published today in Nature, complements other evidence of early life found last year in 3.71-billion-year-old fossil stromatolites in Greenland.

The findings suggest that while the Earth was only very young, life colonised not only the shallows but also the ocean depths.

But an Australian scientist working on the earlier discovery is not convinced the new find is proof of ancient life.

Although it is not known where or when life on Earth began, some of the earliest habitable environments may have been underwater vents.

To search for life in these settings the team analysed iron-rich quartz rocks from the Nuvvuagittuq belt of northeastern Canada, an ancient hydrothermal vent system that formed between 3.77 billion and 4.3 billion years ago.

Study co-author Dr Dominic Papineau from University College London said several key microscopic features in these rocks convinced him they were evidence of ancient life forms that fed on iron being spewed from the hydrothermal vents.

"The first line of evidence that we have is their unique structures: they're filaments that are just a few microns in diameter but have tens to hundreds of microns in length, which makes them similar to other filamentous micro-organisms," Dr Papineau said.

Filamentous microorganisms can be found today forming microbial mats inside deep-sea hydrothermal vents.

He said some filaments were twisted and branched like modern microorganisms, while others were surrounded by tubes coated with nanoscale particles of iron oxide — or 'rust'.

The rocks also yielded rosette shapes and granules whose mineral composition suggests they represent the fossilised 'putrefaction' of ancient organisms.

"All animals when they die, when they are fossilised, they are converted into a mineral mass of apatite and carbonate," Dr Papineau said.

"From their compositions and the context that we found them, we believe that these are the mineralised remains of the microorganisms that were there."

These clumps of iron and filaments may be microbial cells similar to microbes found in vent environments today (Supplied: M Dodd)

The researchers said the findings could not only help us piece together the early history of Earth, but search for traces of similar lifeforms in other parts of the solar system such as Mars.

Interpretation of early life is contentious
Professor Martin Van Kranendonk, of the University of New South Wales, was one of the co-authors on the Greenland fossil stromatolite study, which was published in Nature last year.

He said while the current paper had done some "cutting-edge" analysis on the samples, he debated whether the features discovered were biological in origin.

"It's very possible that there was life at that time — I think it's almost certainly the case — but as we delve deeper in the rock record, each interpretation gets more contentious, but here I think the science doesn't hold," said Professor Van Kranendonk.

He argued these rocks would have been subjected to enormous temperature and pressure changes, which could have a range of effects on the minerals contained within them.

"This is where the scale becomes important because at the grain scale there are lots of reactions going, especially when you have lots of different minerals like carbonate minerals that break down," he said.

These structures may have formed through the oxidation of organic matter derived from microbes living around vents. (Supplied: Matthew Dodd)

Professor Van Kranendonk said the tubules, which the authors suggest are one of the main pieces of evidence for biological life, look like they could also be the product of gas or minerals moving through the rock as it recrystallises and leaving behind a trail of materials.

He said it wasn't impossible to discover definitive evidence of biological life in these sorts of formation, but it was challenging.

"We're on a quest to understand our origins and these kind of investigations are fascinating but we have to stay realistic about what we know and don't know," he said.

"We're pushing the boundaries of what science can do."