The Oldest Rocks on Earth Could Contain Signs of Life

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Earth is teeming with life today, but there was a time in the distant past that our planet was as inhospitable as you can imagine. Frequent asteroid and comet impacts during Earth’s first few hundred million years made the surface molten and the air poisonous, but something might have been alive back then. A team of Japanese scientists studying the oldest rocks on Earth has found new evidence to support the existence of life during the “Late Heavy Bombardment” period. To quote Dr. Ian Malcolm, “Life, uh, finds a way.”

Earth’s history is broken up into four eons. We live in the fourth, known as the Phanerozoic. It started 542 million years ago, which is when complex multicellular life began to appear. This is also when macroscopic fossils begin to appear in rock formations. The first era of Earth is known as the Hadean Eon, taking its name from Hades, the Greek god of the underworld. Scientists literally named this time “hell on Earth” because of the apocalyptic conditions. The surface was regularly vaporized by large impacts, including one that most likely created the moon.

It seems hard to believe that something could live in such an environment, but scientists have been looking at ancient rocks in northern Canada and southern Greenland to find out for certain. In this most recent study, geologists from the University of Tokyo surveyed rocks from the Labrador region of Canada. These rocks are as old as 4 billion years, only half a billion younger than the Earth itself. Surprisingly (and controversially), the team reports evidence of long-dead organisms in the rock.

According to lead researcher Tsuyoshi Komiya, the rocks extracted from Canada contain traces of biogenic graphite (see above). Over the course of billions of years, microscopic fossils would have been compressed and heated. The predicted result of such a process is small flecks of graphite like those found in the Japanese team’s samples.

What the Hadean Eon might have looked like. Credit: Tim Bertelink/Creative Commons

If these are indeed the remains of living organisms, they could be 3.95 billion years old. That could push back the origins of life to the late Hadean Eon, but not all researchers are convinced. The researchers did not directly date the graphite samples to prove they were 4 billion years old. Instead, they relied on geological dating of the rock, inferring that if the rock is 4 billion years old, then the supposed biological remains are as well.

This is an interesting piece of evidence, and some scientists are willing to entertain the possibility that life existed in the Hadean Eon. However, additional dating will be required to make this the scientific consensus.

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