Oldest Fossils Ever Found Confirmed to Be 3.5 Billion Years Old

Apex chert in Western Australia where the oldest fossils were found. akhenatenator [CC by 2.0]/Flickr

UCLA scientist J. William Schopf, who originally unearthed controversial fossils from 3.5-billion-year-old rocks back in 1982, has been vindicated, reports Phys.org. The fossils are, indeed, the oldest ever discovered, and they officially push back the origins of life on Earth to a time previously deemed impossible.

When they were first described in 1993, Schopf's fossils were controversial because it was unclear whether they were truly biological. For one, they're tiny — technically referred to as "microfossils" because they can't be identified with the naked eye — and it's not easy to distinguish them from similarly shaped microscopic mineral deposits. They were also found in rocks from an ancient layer called the Apex chert in Western Australia, which dates to when the planet itself was "only" about 1 billion years old. (The Earth itself is thought to be about 4.5 billion years old.)

The fossils were confirmed with the use of a secondary ion mass spectrometer (SIMS) located at the University of Wisconsin, Madison, one of just a handful of such instruments in the world. The carbon composing each fossil was separated into its constituent isotopes and measured. Researchers were able to painstakingly distinguish the carbon isotopes characteristic of life from those that are merely characteristic of lifeless rock.

"The differences in carbon isotope ratios correlate with their shapes," explained John W. Valley, one of the UW-Madison researchers who performed the analysis. "If they're not biological, there is no reason for such a correlation. Their [carbon isotope] ratios are characteristic of biology and metabolic function."

The analysis was able to pick out up to 11 microbial specimens from five separate taxa. Some represent now-extinct bacteria and microbes from a domain of life called Archaea, while others are similar to microbial species still found today.

"I think it's settled," proclaimed Valley.

That life could have been so developed at 3.5 billion years ago means that its origin on Earth must have happened even earlier than that, possibly as early as 4.3 billion years ago, not long after the planet's formation. The finding offers hope for the idea that life is common throughout the universe.

"People are really interested in when life on Earth first emerged," said Valley. "This study was 10 times more time-consuming and more difficult than I first imagined, but it came to fruition because of many dedicated people who have been excited about this since day one ... I think a lot more microfossil analyses will be made on samples of Earth and possibly from other planetary bodies."