| Complex life pushed back in time|
|Multicellular organisms existed on earth more than 400 million years earlier than previously thought, an international team of geologists has revealed.|
The finding, published today in the Proceedings of the National Academy of Science, comes out of research aimed at ending controversy over the age of the Vindhyan basin in central India.
The controversy concerns two fossil discoveries in 1998, which gave conflicting views over when the Vindhyan sedimentary basins, which spread over more than 100,000 square kilometres of central India, were formed.
At the time, Indian geologist Dr Rafat Azmi reported finding small, shell-like fossils, which were typical of those that date to the Cambrian era about 500 to 600 million years ago.
However, German researcher, Dr Adolf Seilacher, discovered a network of mini-tunnels that he claimed were the trace fossils of complex, worm-like organisms estimated to be about 1.2 billion years old.
In today's paper, the authors, who include Australian researcher Professor Birger Rasmussen, say the discrepancy in the two reports had "profound implications" for geological dating and needed to be resolved.
They say that errors, which were later discovered in Azmi's reports, "were taken to suggest they were fundamentally flawed and that the skeletal fossils did not exist".
However, in today's report the authors say Azmi's fossils are real, and are more than a billion years older than he claimed.
The discovery is important as it gives new insight into the earth's biosphere in the Palaeoprotorezoic era, 1.6 billion years ago.
Rasmussen, of Curtin University in Perth, says the size of the fossil tubes is consistent with them being the traces of multicellular eukaryotic algae.
"Previously accepted multicellular eukaryotes were only known from the late Mesoproterozoic or early Neoproterozoic (some 400 to 600 million years later)," the team writes.
"Put simply it shows there were more complex organisms around earlier than we thought," Rasmussen says.
For the study, members of the team travelled with Azmi to collect specimens, which were then analysed in Sweden and Australia.
In Australia, Rasmussen dated the fossils by analysing the decay of uranium inside zircon crystals, while in Sweden they used electron radiation x-ray tomographic microscopy to date the microfossils.
Rasmussen says both methods found the "likely age of the Lower Vindhyan is from the end of the Palaeoproterozoic about 1700 and 1600 million years ago".
"The fact two difference dating methods gave consistent results is important," says Rasmussen.
He and his colleagues say the Lower Vindhyan "presents a spectacular preservation window into a Palaeoproterozoic biota".
"The Vindhyan deposits offer important new insights into the nature and diversity of life, and in particular, the early evolution of multicellular eukaryotes," they write.
Rasmussen says one of the main factors for this level of preservation may be because the region has not been subject to metamorphosis brought on by conditions such as intense heating.