Deep-sea microbes the first brew of life

Life was brewing deep under the oceans more than three billion years ago, according to scientists who have discovered fossils of an ancient microbe that made its home in superheated water near deep-sea volcanic vents.

The fossils were dug out of sulphide deposits in the Pilbara Craton region of Western Australia, an area once at the bottom of a deep ocean. These deposits are associated with hydrothermal vent systems, volcanic openings in the seafloor that spew out chemicals and gases at very high temperatures.

The discovery of fossil remains of these twisting, thread-like organisms was made by Dr Birger Rasamussen and colleagues from the University of Western Australia, Nedlands, and is reported in the journal, Nature. If dated accurately the fossils push back the known range of undersea life by more than 2.7 billion years to 3.235 billion years ago, possibly less than a billion years after the Earth itself formed.

Conditions adjacent to hydrothermal vents are extremely harsh. Seabed temperatures approach 100 degrees and sulphur-based chemicals taint the nearby waters. There is no sunlight so these would not have been photosynthesising organisms.

Things are little different today, however, for the microbes that colonise the volcanic vents along the mid-Atlantic rift. They thrive in the heat and take sustenance from the chemical soup that surrounds them, almost certainly in the same way that their ancestors did billions of years ago.

Scientists have speculated that these deepwater organisms which could survive without sunlight preceded the evolution of photosynthesising organisms. Surface microbes can live only in the sunlight, inhabiting shallow waters or floating on the oceans. Their habitats so close to the surface, however, leave them exposed to the cataclysmic, life-destroying impacts of incoming comets and asteroids. These were plentiful during the Earth's first two billion years and major impacts would have sterilised the surface repeatedly. There was a much greater chance of survival for those organisms clinging to life on the sea floor.

Scientists have speculated that the deep-water colonies kept life on Earth going by replenishing the supply of living organisms after such impacts, eventually leading to life on the surface as we know it today.