An article published in the journal “Proceedings of the National Academy of Sciences” describes a research on microfossil from the Pilbara Formation, Australia, dated about 3.496 billion years old. A team led by J. William Schopf, of the University of California at Los Angeles (UCLA), and John W. Valley, of the University of Wisconsin at Madison, subjected these microfossils to a very sophisticated examination concluding that they represent well-diversified species. Their deduction is that life on Earth must have been born much earlier and this suggests that it could be common in the universe.
J. William Schopf is a paleobiologist who for decades – he was born in 1941 and started working at UCLA in 1968 immediately after earning his PhD – has been conducting research on the origin of life on Earth. During these decades he discovered some of the oldest existing fossils, exactly the Apex chert microfossils, in the Pilbara Formation, which he described in an article published in the journal “Science” in 1993.
Traces so ancient are really difficult to identify with certainty and in the following years there were a number of arguments around the microfossils discovered J. William Schopf’s team, which according to other researchers were the product of geological and not biological processes. Schopf conducted follow-up studies on those microfossils and this time he examined them with a very sophisticated technique called secondary ion mass spectrometry (SIMS) to examine the carbon isotopes present in those rocks.
In 2000, J. William Schopf was the first to use SIMS to analyze microfossils so there are now several precedents in this application of very modern technologies to paleontology and paleobiology studies. In this specific case, the examination of carbon isotopes is useful because living organisms have a different ratios with respect to that typical of the Earth’s crust and different species have different ratios between them.
The isotopic ratios, in this case between carbon-12 and carbon-13, can also help the identification if not of a species at least of one group of organisms. That’s because in the various taxonomic groups the carbon isotopes are present in rather specific ratios that help to recognize them.
First of all, the samples examined by the researchers showed isotopic ratios different from those of the rock around them with values connected to their shape. That’s a strong indication that those really are microfossils generated by biological processes because geological processes would produce samples with ratios similar to those of the rock around them.
The analysis of isotopic ratios suggests that those microorganisms were very different from each other, even belonging to different domains of life. In fact, according to the researchers, two of them were bacteria capable of photosynthesis, one was an Archaeal methane producer, and two others were methane consumers. At the time, methane was an important component of the Earth’s atmosphere.
That diversity in such ancient organisms indicates that life on Earth must have been born long before, perhaps even 4 billion years ago, and that it developed considerably under conditions that were very different from the current ones, for example with very little oxygen. This suggests that the presence of elementary life forms can be widespread in the universe while more complex life forms require more favorable conditions.