Dating billion year old rocks
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.
The scientists determined the age of the rocks through radiometric dating, measuring the abundance of elements created by the steady decay of uranium.
[Lucy, our hominid cousin, may have died in a tragic fall from a tree] Claims about evidence for ancient life have invariably been controversial.
The multiple lines of evidence for the Greenland stromatolites "are not as clear cut as you’d ideally want for such an extraordinary claim," cautioned Abigail Allwood, a geologist at the NASA Jet Propulsion Laboratory who has studied fossil stromatolites.
Fossilized stromatolites nearly 3.5 billion years old have previously been found in Western Australia.
Those fossils have until now been the oldest widely accepted evidence for life on Earth.
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.
If we found these on Mars, would we plant a flag and declare that we had found life on Mars? There will be people surely who will put forward alternative hypotheses.
Some researchers have cited signatures of life from an even earlier time, including in the Isua formation in Greenland, but typically these assertions have involved biologically friendly molecules rather than actual fossils.
Moreover, very old rocks — older than 3 billion years — are exceedingly rare, because the Earth's surface has been eroded over time and recycled through plate tectonics.
Microbes capable of performing photosynthesis and forming communities are relatively sophisticated organisms.
They presumably had less-sophisticated ancestors that lived more than 4 billion years ago, the Nature paper states.At one point, a Mars-sized object slammed into the Earth and blasted into space the material that eventually cohered into the moon.