From the New York Times in the USA:
Team Claims It Has Found Oldest Fossils
By NICHOLAS WADE
Published: August 21, 2011
A team of Australian and British geologists have discovered fossilized, single-cell organisms that are 3.4 billion years old and that the scientists say are the oldest known fossils on earth.
Their assertion, if sustained, confirms the view that life evolved on earth surprisingly soon after the Late Heavy Bombardment, a reign of destruction in which waves of asteroids slammed into the primitive planet, heating the surface to molten rock and boiling the oceans into an incandescent mist. The bombardment, which ended around 3.85 billion years ago, would have sterilized the earth’s surface of any incipient life.
The claim is also a new volley in a long-running conflict over who has found the oldest fossil.
The new microfossils are described in Sunday’s issue of Nature Geoscience by a team led by David Wacey of the University of Western Australia and Martin D. Brasier of the University of Oxford. The fossils were found in sandstone at the base of the Strelley Pool rock formation in Western Australia.
See also here.
Eight million, seven hundred and four thousand eukaryote species share this planet, give or take 1.3 million. Eukaryotes have cells with nuclei and other membrane bound structures, which means bacteria and other simple organisms were excluded from the count: here.