In 1982, UCLA scientist J. William Schopf collected samples from the Apex Chert in Western Australia—a rare outcropping that has not changed much since it formed 3.5 billion years ago, just a billion years after the formation of the solar system. In 1993, Schopf described what he believed were microfossils in the rock; the oldest-known fossils ever discovered. But not all were convinced of the find.
As George Dvorsky at Gizmodo reports, more analysis took place in 2002, but still not enough to satisfy critics who believe the “microbes” are just minerals. Now, a new detailed analysis of the suspected fossils seems to support that they are indeed real, but controversy over the fossils still remains.
Researchers re-examined the specimens using cutting edge technology at the University of Wisconsin, Madison, to measure the ratio of carbon isotopes preserved within, comparing the signatures to the surrounding rock. Carbon comes in a few different flavors, or isotopes, and life leaves a particular signature in the ratio of these different types of carbon, namely carbon-12 and carbon-13.
By comparing their measurements to a fossil-free section of rock, researchers found the characteristics of biologic life in the C-13/C-12 ratios of the tiny fossils. The team was also able to tease out even more information from the measurement about the life mode of these tiny lifeforms. They believe that the 11 samples studied represent five different species and included photosynthesizers that produces energy from the sun, one Archaeal methane producer and two methane consumers (gamma proteobacteria). They described their find this week in a study published in the journal Proceedings of the National Academy of Sciences.
The find has significance for the search for extraterrestrial life. “By 3.465 billion years ago, life was already diverse on Earth; that’s clear — primitive photosynthesizers, methane producers, methane users,” Schopf says in a UCLA press release. “This tells us life had to have begun substantially earlier and it confirms that it was not difficult for primitive life to form and to evolve into more advanced microorganisms…But, if the conditions are right, it looks like life in the universe should be widespread.”
To find the oldest fossils on Earth has become something of a race—and not everyone is yet convinced by Schopf’s fossils. As Dominic Papineau of University College London tells Dvorsky, the team has done good work. But he disputes the claim that the samples are the oldest fossils; he believes that he, in fact, found 3.95-billion-year-old fossils in Labrador earlier this year. Another team claims to have found 3.77-billion-year-old microbes in Greenland.
David Wacey, researcher at the University of Western Australia who found what is believed to be a 3.4-billion-year-old fossil also in Australia, claims that the new work has many flaws. He says the researchers over-interpret their data and that there is previous evidence that this type of spectroscopy does not have the spatial resolution to analyze the carbon properly. He also points out that the material was also peer-reviewed by a student and former collaborator of Schopf, which is not standard procedure.
It’s likely that scrutiny will continue for these fossils. Birger Rasmussen, a geobiologist at Curtin University in Perth, Australia, who is not involved in the study, tells Elizabeth Pennisi at Science he hopes the work will continue. “It’s worth getting this right, given that we are looking at some of the oldest possible traces of life,” he says. “Honing our skills at recognizing ancient biosignatures on Earth is important as we cast our eyes to Mars and beyond.”
It's unclear if the claims of such early life will hold up in the long run, but each step researchers take to better understand the conditions in which life evolves—and the extreme environments in which it can thrive—is another step toward answering the question: Are we alone in the universe?