Scientists Discover Oldest Fossils on Earth

A team of Anglo/Australian scientists have published their findings regarding the discovery of tiny, microbial fossils that could be the oldest fossils ever found on Earth.  The discovery in 3.4-billion-year-old sandstone, some of the oldest sedimentary rock known, suggests that bacteria had evolved early in the Archaen Eon a time when the Earth was virtually devoid of oxygen.  The discovery was made at the remote Strelley Pool location, Pilbara (Western Australia).  Not only does this discovery have significant implications for life on our own planet but such a find could help scientists search for evidence of microbial life on Mars.

Oldest Fossils on Earth

Pictures of the remote fossil location have been distributed, a site synonymous with Archaen microbial fossils.

The new research, published in the scientific journal “Nature Geoscience”, provides solid fossil evidence to date key branching points in the Earth’s evolutionary clock, although as with many microbe fossils, some scientists are challenging whether the tiny tube-like structures that have been discovered are organic remains suggesting that they could have been formed by chemical or other inorganic means.

Scientists based in The University of Western Australia’s Centre for Microscopy, Characterisation and Analysis in collaboration with Oxford University (England) have unearthed arguably the best-preserved pre-three-billion-year-old micro-fossils on Earth.  These consist of remarkably preserved carbonaceous cells along with the protective tubes (sheaths) that housed some of these cells.

Leading author University of Western Australia Postdoctoral Research Fellow Dr David Wacey said direct evidence for early life in the form of micro-fossils was exceedingly rare and evidence for what type of life came first had until now proved elusive.  Certainly, from what is known about the Archaen Eon, any life forms that may have lived during this immensely ancient time were likely to have been extremely tough – extreme extremophiles as it were.

Dr Wacey commented:

“Our research helps to answer the question: How did these microbes survive?  On the early Earth, where free oxygen was rare or absent, evolving life had to employ other means to survive.  Using a combination of electron microscopy and ion probe analysis, we were able to show that these particular microbes had a metabolism that was based on the use of sulphur.  This ability to essentially ‘breathe’ sulphur compounds has long been thought to be one of the earliest stages in the transition from a non-biological to biological world.”

The conditions that early life forms may have evolved in can still be found on our planet today.  Just a few decades ago marine biologists discovered a series of volcanic vents on the bottom of deep oceans.  These “black smokers” as they are called as they belch out columns of dense, black smoke rich in iron sulphides at temperatures of more than 400 degrees Celsius could mirror the conditions where the first life on Earth evolved.   Life may have thrived around such undersea vents, building a sulphur based ecosystem.

Dr Wacey went onto state:

“By showing the intimate association of these 3.4 billion-year-old micro-fossils with the mineral pyrite (FeS2), we have now provided the earliest direct evidence of micro-organisms employing a sulphur-based metabolism.”

The micro-fossils come from Strelley Pool, a remote region of the Pilbara about 60 kilometres west of the small town of Marble Bar (Western Australia).  They are the oldest micro-fossils ever to be found in sandstones, extending the record of life on Earth in such rocks by about 300 million-years.

Pictures show a computer generated 3-D model of a micro-fossil about 10 micrometres in diameter from Western Australia (left).  Cross sections through the reconstruction (right) emphasise the spheroidal nature of this ancient cell.

For models of prehistoric animals and other creatures: Replicas of Extinct Creatures.

Images show a highly magnified collection of tubular micro-fossils (resembling the protective sheaths of modern bacteria) found in between sand grains in a 3.4-billion-year-old sandstone from Western Australia

A team member, Martin Brasier, of Oxford University, made the additional claim that the remains were the Earth’s oldest fossils.

He said:

“At last we have good solid evidence for life over 3.4 billion years ago.”

However, as with a number of such discoveries dating from 3.49 to 3.4 billion years ago this research has attracted controversy.  Although the Strelley Pool area has provided evidence of micro-fossils such as simple bacteria filaments, a number of scientists question the findings.  Professor Brasier has been a leading critic of slightly older fossils, found in the Pilbara in 1993 by a Californian researcher, William Schopf.  He has argued these older fossils are not biological in origin, as Professor Schopf believes.

If the Strelley Pool discoveries are proof of ancient life on Earth then this evidence could assist scientists as they seek to discover if there was life on Mars.  Using this information, they could look for geological features that resemble the Pilbara location on the red planet and then aim to send unmanned probes to sample rock cores to see if the chemical signatures of micro-fossils could be found.

To read an Everything Dinosaur blog post on fossils that indicate the oldest animals known to science: The Oldest Animal Fossils.