A team of American, British and Australian scientists has uncovered evidence that life may have originated on earth at least 350 million years earlier than previously believed, at a time immediately after a devastating bombardment by meteors.
The discovery complicates the question of when and how terrestrial life arose. Recent studies based partly on the distribution of craters on the moon have suggested that a rain of meteors smashing into the early earth was intense enough until 3.8 billion years ago to destroy all life on the planet, if any existed at that time. The oldest objects believed to be the fossils of living organisms - tiny mineral filaments - are estimated to be 3.5 billion years old.
But findings reported today in the journal Nature imply that the window of time between the end of the lethal meteor bombardment of the young earth and the beginning of life may have been vanishingly short. The work suggests that life had already established a toehold on the infant planet 3.85 billion years ago.
In a comment also published by Nature, Dr. John M. Hayes of the Woods Hole Oceanographic Institution in Massachusetts, said the investigation seemed to imply that biochemical processes “developed with breath-taking rapidity after the last large impact.”
Many scientists believe that the chemical processes that gave rise to life must have taken hundreds of millions of years to develop the essential enzymes, proteins and genetic codes. Evidence of a very quick beginning might mean that there was too little time to complete the job on earth, and that life therefore must have originated elsewhere, drifting through space to the earth in the form of spores or by some other means. This is known as the “panspermia” theory.
The discovery reported today was by a group headed by Dr. Gustaf Arrhenius of the Scripps Institution of Oceanography at San Diego. (Arrhenius is the grandson of Svante Arrhenius, the renowned 19th-century Swedish scientist whose work laid much of the basis of modern chemistry and who believed that life originated somewhere other than the earth.)
The focus of their investigation was a formation known as the Isua supracrustal belt of Akilia Island in southern West Greenland. The formation had been dated by radioactive decay techniques at 3.85 billion years old, the oldest known rocks in the world.
The discovery did not include any actual fossils. It is believed that no fossils could survive from such ancient times.