23 October 2008
Research paper published in 23 October 2008 issue of Nature
Research by Curtin University of Technology’s Professor Birger Rasmussen and Dr Ian Fletcher, working in conjunction with Dr Jochen Brocks (The Australian National University) and Dr Matt Kilburn (The University of Western Australia) has significantly rewritten the early history of major groups of life and the rise of atmospheric oxygen on Earth.
These research findings, presented in the paper “Reassessing the first appearance of eukaryotes and cyanobacteria”, were published in the prestigious international science journal Nature on 23 October 2008.
The research re-examined chemical signatures from 2.7 billion year old rocks, known as biomarkers, which were previously considered to provide the oldest evidence for eukaryotes (organisms with nucleated cells) and cyanobacteria (microbes that produce oxygen by photosynthesis), and indirect evidence for the emergence of oxygenic photosynthesis – a critical event that changed the Earth’s atmosphere and allowed the evolution of new life forms dependent on oxygen, including ultimately humankind.
Professor Rasmussen explained that the biomarkers have raised several puzzling questions since they were first reported a decade ago, particularly because they suggested a much earlier appearance of these life forms than other geological evidence.
“The biomarkers appeared to be 400 million years older than other evidence for the emergence of oxygen-producing cyanobacteria and the rise in atmospheric oxygen, and a billion-years older than fossil evidence for eukaryotic organisms,” Professor Rasmussen said.
Detailed analysis by the Curtin-led team using a NanoSIMS ion microprobe has indicated that the biomarkers probably represent contaminants, presumably introduced from younger sedimentary rocks, or during drilling or sample handling.
“Our work shows that the biomarkers used previously to date the appearance of cyanobacteria and eukaryotes, and the advent of oxygenic photosynthesis, are younger than the 2.7 billion old rocks in which they are found,” Professor Rasmussen said.
“In the absence of the biomarker evidence, the oldest unambiguous fossil evidence for cyanobacteria is only about 2.2 billion years old, while the oldest probable eukaryotic fossils are about 1.7 billion years old, both significantly younger than the 2.7 billion year age proposed previously.”
He highlighted that the results not only resolve an apparent discrepancy between the biomarkers and other evidence, but also change the map of early life by allowing the first appearance of eukaryotes to be well after the rise in atmospheric oxygen.
“We now have an answer to the long apparent delay between the first chemical evidence for eukaryotes and oxygen-producing cyanobacteria, and the first geological record of these events – the chemical evidence is of uncertain age and almost certainly younger than previously believed,” Professor Rasmussen said.
The group now plans to use NanoSIMS to analyse additional samples and apply rigorous new sample preparation techniques developed by Dr Brocks that completely remove contaminants. These techniques will be used to identify authentic biomarkers and improve our understanding of the nature and diversity of ancient life.
Modified: 23 October 2008