SYDNEY • Life on Earth is even older than we thought, Australian scientists said yesterday as they unveiled fossils dating back a staggering 3.7 billion years.
Experts are likely to debate whether the structures called stromatolites - preserved in rocks along the edge of Greenland's ice cap - were formed biologically or through natural processes. If biological, the great age of the fossils complicates the task of reconstructing the evolution of life from the chemicals naturally present on the early Earth. It leaves comparatively little time for evolution to have occurred.
The fossils were found four years ago but not publicised while the geologists, a team led by Professor Allen Nutman of the University of Wollongong, checked out their find. They prove that life emerged just a few hundred million years after the Earth was formed some 4.5 billion years ago, Dr Nutman said.
"This discovery represents a new benchmark for the oldest preserved evidence of life on Earth," Professor Martin Julian Van Kranendonk, a geology expert at the University of New South Wales and one of the study's co-authors, said. "The structures and geochemistry from the newly exposed outcrops in Greenland display all the features used in younger rocks to argue for a biological origin. It points to a rapid emergence of life on Earth."
The 1cm- to 4cm-high Isua stromatolites - exposed after the melting of a snow patch in the Isua Greenstone Belt - matched other biological evidence on the evolution of the genetic code that placed the origins of life in a similar period. Dr Nutman also said the discovery could help the hunt for life on Mars, considered the most likely location for microbial life-forms among other planets in the Solar System.
"The significance for Mars is that 3,700 million years ago, Mars was probably still wet and probably still had oceans and so on, so if life develops so quickly on Earth to be able to form things like stromatolites - it might be more easy to detect signs of life on Mars," Dr Nutman said.
An expert on the early Earth's environment, Dr Tanja Bosak of the Massachusetts Institute of Technology, said the structures do resemble modern stromatolites but that their origin "will be hotly debated", given there is no sign of certain features that might bolster the case for biological origin, such as crinkling in the layers of sediment.
The Greenland stromatolites are some 220 million years older than the oldest previously known fossils, also stromatolites. Those are 3.48 billion years old and were discovered in Western Australia in 2006.
The latest findings were published in the journal Nature.
AGENCE FRANCE-PRESSE, NEW YORK TIMES