Life appears to have formed on Earth much earlier than previously believed, during a time when the planet's oceans were green and skies were orange, reports New Scientist.
Researchers found fossils that were dated at 3.7 billion years old — the oldest fossils ever found — in a newly exposed rock formation in Greenland. The creatures revealed in the fossils look like stromatolites, tiny layered mounds just a few centimeters tall that are known to be formed by photosynthetic microbes living in water.
The find was made possible due to expanded ice melt on the Greenland continent, which is exposing rocks buried beneath Greenland's ice for ages. The fossils were found in a region of southwest Greenland called the Isua supracrustal belt, a place that has remained relatively safe from geological processes that churn the crust and renew the Earth's features and bury the record of its history.
“This is one of the extremely few places where this kind of feature could still be preserved in the rock record,” explained Allen Nutman of the University of Wollongong in Australia, who led the team.
The fossils are the oldest fossils ever found by 220 million years. The Earth was so new at the time that it gives hope to astrobiologists seeking evidence for the emergence of life on other planets such as Mars and Venus.
Stromatolites are fairly complex structures that are still made by microbes alive today. Their complexity indicates that these were probably not among the first organisms to evolve; they would have been part of a vast biota with a history that stretches back even further than the fossils' 3.7 billion-year-old date suggests. In other words, life would have had to have emerged on Earth even sooner than this for such complicated lifeforms to have evolved.
“What we have in Isua is just a tiny sample of any life that may have been around at that time,” said Nutman. “It would be like going to somewhere on Earth now and picking up some shells from a beach and getting the impression, ‘Oh, that’s the full diversity of life that is on the planet’.”
Since stromatolites are structures made by organisms, not impressions of the organisms themselves, more research will be needed to confirm that they are, in fact, proof of life. But it's an exciting find nonetheless, one that proves that the history of life on Earth is a complicated one indeed.