Are These Earth's Oldest Fossils or the Result of Minerals?

Though the photograph below may look like dried up water marks, scientists claim they represent the oldest fossils on Earth.

Found in Australia by researchers with the University of Western Australia and Oxford University, these microscopic fossils are sulfur bacteria cells. The sedimentary rock in which the cells were found allegedly dates back to 3.4 billion years ago, leaving some scientists claiming that was life on an early, oxygen-free world.

But microfossil identification can be a hot topic. It can be difficult to discern if the fossils were created by living cells or nonbiological processes, like mineral deposits. The researchers, as reported by the New York Times, believe they've nailed these as bacteria though:

Cell-like structures in ancient rocks can be deceiving — many have turned out to be artifacts formed by nonbiological processes. In this case, the geologists have gathered considerable circumstantial evidence that the structures they see are biological. With an advanced new technique, they have analyzed the composition of very small spots within the cell-like structures. “We can see carbon, sulfur, nitrogen and phosphorus, all within the cell walls,” professor Martin Brasier of Oxford University said.

Crystals of fool’s gold, an iron-sulfur mineral, lie next to the microfossils and indicate that the organisms, in the absence of oxygen, fed off sulfur compounds, Brasier and his colleagues say.

The New York Times also states that contention in identifying microfossils could arise among scientists who have already claimed to have found the oldest fossils:

The honor of having found the most ancient microfossil has been long been held by J. W. Schopf, a paleobiologist at the University of California, Los Angeles. In 1993, Schopf reported his discovery of fossils 3.465 billion years old in the Apex chert of the Warrawoona Group in Western Australia, about 20 miles from where the new fossils have been found. Those would be some 65 million years older than the new find, but Dr. Schopf’s claim was thrown in doubt in 2002 when Brasier attacked his finding, saying the fossils were not biological but just mineral artifacts.

According to Oxford's press release, the researchers believe this finding could have implications for finding life on other planets. If there were life on other planets, researchers say it would look similar to this. The findings were published in the latest issue of Nature Geoscience.

[H/T Science Daily]