Earliest traces of complex life?Cosmic Log: Scientists say they've discovered fossils in Gabon that may represent the earliest-known multicellular life, dating back 2.1 billion years... The traces of microbial life appear to go even further back in time -- to 3.45 billion years ago, based on the way that mats of organic material have built up in ancient sediment. In the multicellular category, the oldest candidate has been a 2 billion-year-old, centimeter-scale, coil-shaped fossil known as Grypania spiralis, which might have been a giant bacterial or algal creature.
The new discoveries, described in the journal Nature, show more evidence of structure and measure as large as 12 centimeters in size... The researchers, led by Abderrarazak El Albani of the University of Poitiers... collected more than 250 fossils from a well-known geological formation in the West African country of Gabon, and put them through rounds of micro-CT scans to chart their 3-D structure. Based on that structure, the researchers deduce that the organisms were built up through cell-to-cell signaling -- and not merely deposited together as a microbial mat...
The 2.1 billion-year mark is significant because scientists think Earth's atmosphere made a major transition around 2.4 billion years ago. Before that time there appears to have been no oxygen in the air. Even 2.1 billion years ago, 'the atmosphere was still a toxic mix of greenhouse gases, with oxygen making up only a few percent of modern levels, Donoghue and Antcliff note [in a Nature commentary on the research].
'This bacterial world was undergoing the greatest episode of climate change in the history of the planet: pumping out oxygen, drawing down carbon dioxide, slowly transforming the Earth into the world we know.'
