Fossils found in China show life began more than billion ago
The researchers doing a study on fossils said they had uncovered fossils showing that complex life on Earth began more than billion years ago. Seaweed-like fossils found in rocks in China dated to around 1.56 billion years ago are the earliest known examples of larger organisms made up of many cells built like our own.
A claim by researchers that complex life on Earth might have evolved a billion years earlier than previously thought, has immediately divided scientists in the field with some hailing the evidence as rock-solid and others unconvinced.
After first emerging from the primordial soup, life remained primitive and single-celled for billions of years, but some of those cells eventually congregated like clones in a colony. Scientists took to calling the later part of this period the “boring billion” because evolution seemed to have stalled.
But at some point there was a leap – arguably second in importance only to the appearance of life itself – towards complex organisms with multiple cells.
This transition progressively gave rise to all the plants and animals that have ever existed.
Exactly when multi-celled “eukaryotes” – organisms in which differentiated cells each
contain a membrane-bound nucleus with genetic material – showed up has inflamed scientific passions for many decades.The fossils were uncovered in the Yanshan region of Hebei province in China. Zhu and colleagues said they had found 167 measurable fossils, a third of them in one of four regular shapes – an indication of complexity. The largest measured 30cm by 8cm.
Taken together they were “compelling evidence for the early evolution of organisms large enough to be visible with the naked eye”, said Zhu.
“This totally renews current knowledge on the early history of life.”
Previously, eukaryotes of comparable size had not been known to appear in the fossil record until about 600m years ago, when a multitude of soft-bodied creatures inhabited the world’s oceans.
Phil Donoghue, a professor of palaeobiology at the University of Bristol, described the discovery as a “big deal”.
“They are not the oldest eukaryotes, but they are certainly the oldest demonstrably multicellular eukaryotes,” he said.
Their very existence 1.56bn years ago would mean that “oxygen levels were sufficiently high to allow for such large organisms to subsist”.
But other experts were more sceptical.
“There is nothing here to suggest that the specimens are eukaryotic, as opposed to bacterial,” said Jonathan Antcliffe, a senior researcher in the University of Oxford’s department of zoology. Bacteria are, by definition, unicellular, and do not have distinct nuclei containing genetic material.
Antcliffe suggested the fossils were more likely corresponded to colonies of bacterial cells, rather than a single complex organism.
Truly multicellular creatures display three-dimensional form in which only some cells are in direct contact with the environment.
The fossils discovered in China show it was possible for some eukaryotes to become large and complex despite those constraints. Indeed, the long stable period may have been essential for eukaryotes’ development, some researchers say.
As Martin Brasier, the late University of Oxford palaeobiologist, once told the New Scientist: “I argue that the boring billion was the anvil on which the eukaryote cell was forged.”
