Ediacaran sea floor, Namibia, Southwest Africa, 543 million years ago.
Credit: Museum of Natural History, University of Oxford / Mighty Fossils.
New study suggests animals may have evolved vastly earlier than fossil evidence suggests | Oxford University
One of the strengths of science is that its conclusions remain open to revision. An assumption that once appeared reasonable can be tested against new evidence, found wanting, and replaced with something better. For creationists, who frequently portray such revisions as evidence that science cannot be trusted, this must seem a peculiar way of acquiring knowledge. Yet it is precisely how science improves its understanding: by allowing the evidence to correct the explanation, rather than requiring the evidence to conform to a predetermined answer.
A new study published in Science Advances provides another example. Researchers have challenged an assumption used in some recent estimates of when animals originated. Their analyses support an origin approximately 700–800 million years ago, potentially extending animal evolutionary history by around 200 million years beyond estimates based on a younger maximum-age constraint.
The issue is a deceptively simple one: if a fossil deposit preserves microscopic organisms in exquisite detail, but contains no definite animals, does that mean animals had not yet evolved? Some researchers have used the approximately 590-million-year-old Weng’an Biota of China in this way, reasoning that animals would have been preserved there had they existed. Its lack of unequivocal animal fossils has therefore helped set a proposed upper age limit for animal origins.
The new research exposes a difficulty with that reasoning. The younger Kheseen Biota of Mongolia also preserves exceptionally detailed microfossils, yet none can confidently be identified as animals. In this case, however, animals are known from other deposits of comparable age. Their absence from Kheseen therefore cannot demonstrate their absence from the world. Particular environments and conditions of fossilisation can leave animals out of the record, even when other organisms are beautifully preserved.
This matters because molecular clocks — methods that use genetic differences between living organisms to estimate when their ancestors diverged — require calibration against geological and fossil evidence. Change an unjustified age constraint, and the resulting estimates can change substantially. Using alternative constraints from older deposits, the researchers recovered a much earlier possible origin for animals. They have not discovered an 800-million-year-old animal, nor established a final date for the animal kingdom’s beginnings. They have shown why one argument for restricting those beginnings to a much later interval is unreliable.
For young-Earth creationism, neither chronology offers any comfort. The debate concerns events hundreds of millions of years ago, not whether animal history can be squeezed into the few thousand years allowed by a literal reading of Genesis. Uncertainty over precisely when animals originated does not make every proposed date equally credible, any more than uncertainty over a mountain’s exact height makes it plausibly a molehill.
