|Bacterial microfossils from the Strelley Pool, Western Australia|
'We can be very sure about the age as the rocks were formed between two volcanic successions that narrow down the possible age to a few tens of millions of years,' stated Professor Martin Brasier, a member of the team currently researching these fantastic fossils, 'that's very accurate indeed when the rocks are 3.4 billion years old.' While these facts are, in themselves, revolutionary, the real question is what were these early life forms using as their energy source?
Oxygen had not appeared in the atmosphere at this time in the Earth's history and therefore these forms could not have photosynthesised. Finding an energy source as abundant as the sun is very difficult indeed. However mineral traces within these rocks may have solved this mystery. Tiny crystals of iron pyrite, more commonly known as Fool's Gold, suggest that these bacteria used sulphur as their energy source. Many bacteria today use sulphur. Such creatures exist in highly anoxic (oxygen lacking) environments, such as hydrothermal vents.
Early fossils are a highly controversial subject. Many possible early fossils are dismissed by many eminent scientists as just microscopic geological anomalies and crystalline formations, similar in structure to simple bacterial cells. These fossils are widely held as the true remains of some of the most ancient bacteria on Earth. They show all the right signs of life, including metabolising structures, cell shape, formation, and are similar to undisputed bacterial cells dating from 2 billion years ago.
They are also clustered in groups similar to the behaviour seen in yeast cells: conducted during an experiment demonstrating how early cells could have clustered together to break down sugar molecules for more efficient metabolism. Such conclusions would have been very controversial several years ago. However breakthroughs in microscopic chemical analysis have changed how we study early fossils. The specimens also open up possibilities as to how life might survive on planets and moons such as Europa or Titan.