300 Posts And Three Billion Years Ago

To the casual observer, the Archaean Earth would have looked devoid of life. It would have been a wasteland of rocks, volcanoes with dust gradually succumbing to the force of the waves, slowly slipping away beneath the oceans. To a microbiologist, however, it would be a veritable rainforest. Blotches and stains around pools of water would be indicative of vast bacterial colonies and under a microscope samples of sand and earth would have been home to countless micro-organisms.

An artist's impression of the Archaean Earth

The challenge to palaeontologists was ascertaining just how complex these microbial communities were. Previously, it was thought that early life was simple and not particularly diverse by the standards of bacterial species today. Yet a fossil discovery in Australia has shown that this view may be far from accurate. Rock samples from the Farrel Quartzite in Western Australia were found to contain three billion year old fossils of plankton.

Of course, when dealing with putative micro-fossils this far back in time, there is a huge margin for error. To prove that the structures within the quartzite were organic in nature, the researchers looked at 15 different samples of Farrel Quartzite and examined their stable carbon isotope ratios. The percentage of carbon-13 in the micro-fossils was indicative of material produced by biological processes. In contrast, the carbon-13 percentage in the background organic matter in the surrounding rock was different from that of the micro-structures.

'When considered along with published morphological and chemical studies, these results indicate that the Farrel Quartzite micro-structures are bona fide micro-fossils, and support the interpretation that the spindles were planktonic.' Their unusual shape also helped lead the researchers to classify the fossils as plankton. Exactly what kind of plankton they are remains to be seen.

Three billion year old planktonic fossils from
the Farrel Quartzite in Western Australia

Indeed the term is often used in a generic sense to refer to both complex (eukaryotic) creatures and simple (prokaryotic) ones. The size of the structures, 20 to 60 microns in length suggests the latter, a prediction which fits with the proposed origins of eukaryotes later in time around 2.6 billion years ago. 'It is surprising to have large, potentially complex fossils that far back," said Christopher H. House from Penn State University. 

The importance of this discovery, apart from showing us the true level of diversity and complexity in the earliest communities of living organisms on the planet, gives us insight into just how widespread life on Earth was just 500 million years after its creation. The researchers noted that similar fossils have been found in 3.5 billion year old localities in South Africa (the Onverwacht Group) and Australia (the Strelley Pool Formation). 

The fact that another locality which is 500 million years younger has similar fossils shows that life on the planet must have been widespread and far more complex than previously thought. This trend of underestimating living organisms has been prominent throughout the history of biology. Scientists thought that life could not survive in extreme heat, pH or the vacuum of space. Then came the discovery of extremophiles capable of living on the very edge. The discovery of fossils of the first, supposedly simple creatures on the planet, hailing from the Archaeon era, will most probaly in time prove equally more complex than first thought.