Fossil bacteria from 3.4 billion years ago are the world’s oldest fossils.
The microfossils were found in a remote part of Western Australia called Strelley Pool. They are very well preserved between the quartz sand grains of the oldest beach or shoreline known on Earth, in some of the oldest sedimentary rocks that can be found anywhere.
They are from a billion years before plants generated our oxygen atmosphere.
The fossils are very clearly preserved showing precise cell-like structures all of a similar size. They look like well known but much newer microfossils from 2 billion years ago, and are not odd or strained in shape.
The fossils suggest biological-like behaviour. The cells are clustered in groups, are only present in appropriate habitats and are found attached to sand grains.
And crucially, they show biological metabolisms. The chemical make-up of the tiny fossilised structures is right, and crystals of pyrite (fool’s gold) associated with the microfossils are very likely to be by-products of the sulphur metabolism of these ancient cells and bacteria.
UPDATE: Jerry Coyne has more details, and more photos, about these fossils. (They may be primitive single-celled organisms rather than bacteria.) Newly found: the world’s oldest fossils . Larry Moran explains the biochemistry that tells us these bacteria digested sulphur in The Oldest Cells.