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Field locations in the Mackenzie Mountains, Northwest Territories, where possible traces of early animal life were collected.
Elizabeth Turner, Laurentian University
The Mackenzie Mountains of the Northwest Territories are home to some of Canada’s most iconic animal species, including grizzly bears and caribou. Now, a Canadian researcher has uncovered evidence that the same location harbours the earliest traces of animal life found anywhere on Earth.
Elizabeth Turner, a professor of sedimentology and paleontology at Laurentian University in Sudbury, Ont., reports that features she discovered in carbonate rocks from the Mackenzie Mountains are likely the remains of sponges that lived in the ocean alongside a vast supercontinent some 890 million years ago.
If correct, the interpretation means the ancestors of modern sponges were on the scene hundreds of millions of years before the formation of the oldest recognized body fossils of other animals.
“We know that animals had to have had a back history – probably a fairly long one,” said Dr. Turner, whose findings were published on Wednesday in the journal Nature.
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A close up of branching structures in 890 million year old rock that have been identified as possible fossilized sponge tissue, making this the oldest remains of animal life currently known.
Elizabeth Turner, Laurentian University
Key to the discovery are worm-like structures measuring less than a centimetre that Dr. Turner spotted while examining thin sections of the rocks. The structures branch and rejoin in a characteristic pattern that resembles the protein skeleton of modern sponges as well as fossilized sponges from more recent eras.
The idea that the structures are mineralized sponge protein fits with genetic data that show sponges are among the simplest and most ancient of animal forms. Estimates suggest the immobile filter feeders could have emerged as early as one billion years ago in a world previously occupied by microbes and algae.
The challenge is that all animals, even those as inert as sponges, need oxygen to support their metabolism. During the time the rocks Dr. Turner examined were formed, the oxygen concentration in Earth’s oceans was far lower than it is today.
This would not be an obstacle if the sponges occupied the fringes of ancient reefs, Dr. Turner said. Such reefs are known to have been built up by bacteria that secrete calcium while producing oxygen through photosynthesis.
“[The sponges] may have been living in what was effectively an oxygen oasis,” she said.
Dr. Turner added that she expects others to challenge her findings, not because they are inconsistent with animal evolution, but because no signs of animal life have previously been reported at such an early date.
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A closeup photo of the internal three dimensional structure of a modern sponge from Greece shows a similar branching pattern. Field of view is approximately 1 millimetre across.
eturner/Elizabeth Turner, Laurentian University
Robert Riding, a geologist at the University of Tennessee, Knoxville who specializes in the same rock type Dr. Turner examined, called the new evidence “very compelling.” He added that the structures documented in Dr. Turner’s study are indistinguishable from those that he and a colleague previously identified as fossil sponge tissue in much younger rocks from Newfoundland and New York state.
“If you compare her material with our material, it’s so similar I can’t tell the difference,” he said.
Dr. Turner said she is continuing her investigations and expects to have more evidence to present. One possible next step will be looking for organic molecules in the samples, which can verify that the patterns have a biological origin.
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