Oldest Fossils Ever Discovered Prove Life on Earth Started Over 3.5 Billion Years Ago

Tuesday, 19 December 2017 - 10:15AM
Tuesday, 19 December 2017 - 10:15AM
Oldest Fossils Ever Discovered Prove Life on Earth Started Over 3.5 Billion Years Ago
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Image credit: John Valley/UW-Madison
Imagine finding the oldest fossils in the world and being told they were just strange minerals.

This is what Professors J. William Schopf and John W. Valley dealt with when they first unearthed a hunk of rock that contained what they suspected were fossils of microscopic organisms from 3.5 billion years ago, each one several times smaller than a human hair.

It took decades of extremely careful research and testing to prove it, but the team emerged yesterday triumphant—they have the proof.

The story of these microfossils began in 1982, when they were extracted from a chert deposit in Western Australia.

The Apex deposit, as it's called, is unique because it has escaped the destructive geological cycles that can incinerate old fossils and completely change the composition of the rock.

Instead, the chert deposit stayed relatively intact, allowing scientists to get a glimpse far back into the past—several billion years in the past. 

In 1993, Schopf first described the microbes he and his team found in the rock in Science, as well as his book Cradle of Life: The Discovery of Earth's Earliest Fossils.

In 2002, he published more evidence backing up his claims, but the deal wasn't sealed until he could prove without a doubt that the 'fossils' were organic. 

It took until December 2017 for all of it to come together in a new study published in The Proceedings of the National Academy of Sciences.

The study uses measurements taken by a secondary ion mass spectrometer (SIMS), which allowed the scientists to measure the ratio between carbon-12 and carbon-13 in the fossils, as well as the surrounding rock.

The ratios, which are different in organic material as compared to inorganic, have proved beyond a doubt that the fossils are indeed genuine, making them the earliest direct evidence of life on Earth. The analysis also allowed the scientists to infer what kinds of microbes they were dealing with:

Opening quote
"The team identified a complex group of microbes: phototrophic bacteria that would have relied on the sun to produce energy, Archaea that produced methane, and gammaproteobacteria that consumed methane, a gas believed to be an important constituent of Earth's early atmosphere before oxygen was present."
Closing quote

Before the SIMS analysis, however, the team had to carefully expose the fossils by grinding down the surrounding rock...one micrometer at a time.

For comparison, the diameter of a human hair can be around 25 micrometers. But no matter how arduous the process was, it was all worth it—we now have a better understanding of early life on Earth, which may end up opening the door to understanding how life develops on other planets.

Hats off to Schopf, Valley, and their tiny, tiny fossils.
Science News
Oldest Fossils Ever Discovered Prove Life on Earth Started Over 3.5 Billion Years Ago