Fossils oldest sign of life on planet, scientists say
Scientists probing a newly exposed, formerly snow-covered outcropping in Greenland claim they have discovered the oldest fossils ever seen, the remnants of microbial mats that lived 3.7 billion years ago.
It’s a stunning announcement in a scientific field that is always contentious. But if confirmed, this would push the established fossil record more than 200 million years deeper into the Earth’s early history, and provide support for the view that life appeared soon after the Earth formed and may be commonplace throughout the universe.
A team of Australian geologists announced its discovery in a paper titled “Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures,” published Wednesday in Nature.
They made their find in July 2012 while doing field research in Isua, a region of Greenland so remote that they had to travel there by helicopter. The site is known for having the oldest rocks on Earth, in what is known as the Isua supracrustal belt.
Allen Nutman, a University of Wollongong geologist who has studied the rocks there since 1980, said one day he and his colleagues were working at the site when they spied some outcroppings they’d never seen before. The formations had been exposed where the snow pack had melted — the result, Nutman said, of the global warming that is so pronounced in Greenland or of low levels of snowfall the previous winter.
They examined the outcropping and saw something intriguing: conical structures less than two inches high. They look like fossilized microbial mats — basically, pillows of slime — known as stromatolites, which are formed today by bacterial communities living in shallow water.
“We all said, ‘ This is amazing. These look like stromatolites,’ ” Nutman said.
Subsequent laboratory analysis established that the formation is 3.7 billion years old, and turned up additional chemical signatures consistent with a biological origin for the conical structures, Nutman said.
Fossilized stromatolites nearly 3.5 billion years old have previously been found in Western Australia.
The Australian researchers do not contend that these stromatolites represent the first examples of life on the planet. Rather, these would have to be the descendants of the earlier life forms.
Earth, along with the other planets in our solar system, formed about 4.5 billion years ago from a cloud of dust and gas swirling around the embryonic sun. For hundreds of millions of years, Earth was a harsh, molten world, heavily bombarded by debris. At one point, a Mars-sized object slammed into the Earth and blasted into space the material that eventually cohered into the moon.
No one knows how life began on Earth.
Charles Darwin hypothesized that life emerged in a “warm little pond,” but other researchers imagine that it emerged around a deep- sea hydrothermal vent, or even came to Earth from space.