Complex Life Started Nearly a Billion Years Earlier Than We Thought
janrinok writes:
New research has uncovered that complex life began forming much earlier, and across a longer timeframe, than scientists had previously assumed. The findings offer fresh insight into the environmental conditions that shaped early evolution and call into question several longstanding scientific ideas in this field.
Led by the University of Bristol and published today in Nature (December 3), the study reports that complex organisms arose well before oxygen became abundant in Earth's atmosphere. Oxygen had long been thought to be essential for the development of advanced life, but the results indicate that this requirement may not hold for the earliest stages of evolution.
"The Earth is approximately 4.5 billion years old, with the first microbial life forms appearing over 4 billion years ago. These organisms consisted of two groups - bacteria and the distinct but related archaea, collectively known as prokaryotes," said co-author Anja Spang, from the Department of Microbiology & Biogeochemistry at the Royal Netherlands Institute for Sea Research.
Prokaryotes dominated the planet for hundreds of millions of years before more complex eukaryotic cells emerged. This latter group includes algae, fungi, plants, and animals.
Davide Pisani, Professor of Phylogenomics in the School of Biological Sciences at the University of Bristol and co-author, explained: "Previous ideas on how and when early prokaryotes transformed into complex eukaryotes have largely been in the realm of speculation. Estimates have spanned a billion years, as no intermediate forms exist and definitive fossil evidence has been lacking."
To address these uncertainties, the international team expanded upon the existing 'molecular clocks' technique, which estimates when species last shared a common ancestor.
"The approach was two-fold: by collecting sequence data from hundreds of species and combining this with known fossil evidence, we were able to create a time-resolved tree of life. We could then apply this framework to better resolve the timing of historical events within individual gene families," added co-lead author Professor Tom Williams in the Department of Life Sciences at the University of Bath.
By comparing more than 100 gene families across multiple biological systems and focusing on traits that differentiate eukaryotes from prokaryotes, the researchers began reconstructing the sequence of events that shaped the rise of complex life.
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