World's oldest fossils were found in Greenland
The oldest fossils ever discovered were found in Greenland and probably preserved the first signs of life on Earth.
The Greenland's fossils discovered in 2016 dated to around 3.7 billion years ago and contain evidence of stromatolites – layers of sediment brought together by ancient water-based bacterial colonies. Before the fossils were discovered, the oldest known evidence of life on Earth were 3.48 billion-year-old fossil stromatolites found in the Pilbara region of Western Australia.
The importance of stromatolites is that not only do they provide clear evidence of ancient life, but that they are complex ecosystems. This indicates that microbial life was already diversified as early as 3.7 billion years ago. This diversity demonstrates that life emerged within the first hundreds of millions of years of Earth's existence, which is in line with biologists' calculations showing the great antiquity of the genetics of code of life.
The world's oldest fossils were discovered in the world's oldest known sedimentary rocks, in the Isua Greenstone Belt, which runs along the edge of the Greenland ice sheet. Although these rocks have been studied for decades, the fossils were hidden from view by the constant snowfall and observed for the first time only in 2016. The fossils contain tiny cones, only 1 to 4 centimeters tall, and their structures and internal layering look exactly like other ancient and modern stromatolites.
The structure of the surrounding rocks suggests that they were deposited at the bottom of a shallow sea, much as stromatolites are today in places like the Bahamas and Western Australia and the rocks contain carbonate minerals such as dolomite, which are common even in younger stromatolites.
If confirmed that these are indeed ancient signs of organisms dating back 3.7 billion years, it will make difficult to explain how evolution could produce such relatively complex organisms so early in the life of the Earth. To have had time to evolve into organisms associated with stromatolite formations, an hypothesis is that life on Earth would likely have originated during the Hadean phase of our planet's history, spanning from the formation of Earth around 4 .65 billion years ago, when debris orbiting the Sun accumulated on our planet until about 4 billion years ago.
But evidence suggests that our planet was constantly bombarded by asteroids so destructive that one even took a chunk off Earth to form our Moon.
Researchers have debated for years about how long these incessant asteroid showers lasted. Probably they likely slowed down over time, making slightly easier the evolution of life.
That may well be the case, but we have evidence of a catastrophic event that saw the Hadean disappear not with one bang, but several bangs, just before the Isua creatures existed. The cataclysm, known as the Late Heavy Bombardment, struck Earth between 3.9 and 3.8 billion years ago.
So how has life evolved through all this chaos?
Link to original publication: https://www.nature.com/articles/nature.2016.20506
