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Study: The oldest animal fossils may be in Canadian rocks

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A Canadian geologist may have found the oldest fossil record of animal life on Earth, according to a report published Wednesday in the journal Nature.

About a billion years ago, an area in northwest Canada now defined by steep mountains was a prehistoric marine environment, and the remains of ancient sponges can be preserved in mineral deposits there, the paper says.

Geologist Elizabeth Turner discovered the rocks in a secluded part of the Northwest Territories accessible only by helicopter, where she had been excavating since the 1980s. The thinner parts of the rocks have three-dimensional structures similar to modern spongy structures.

“I think these are ancient sponges – only this type of organism has this considerate of organic filament network,” said Joachim Rittner, a geologist and sponge expert at Germany’s University of Göttingen, who was not involved in the research.

Dating the adjacent rock strata indicates that the samples are about 890 million years old, making them about 350 million years older than the oldest undisputed sponge fossils ever found.

“The most exciting thing is the timing,” said Paco Cardenas, a sponge expert at Sweden’s Uppsala University, who was not involved in the research. “The discovery of sponge fossils nearly 900 million years ago will greatly improve our understanding of beforetime animal evolution.

Scientists believe that life on Earth originated about 3.7 billion years ago. The oldest animals appeared much later, but exactly when is still up for debate.

Many scientists believe that the first animal groups included soft sponges or sponge-like creatures that lacked muscles and nerves but had other features of simple animals, including cells with divergent functions and sperm.

To date, the oldest undisputed fossil sponge dates back to about 540 million years ago, an era called the Cambrian.

But scientists using a logic line called the molecular clock — which has involved analyzing the rate of genetic mutations dating back as far as when the two species likely diverged — say the available evidence points to sponges appearing much earlier, about a billion years ago.

No supporting physical evidence has yet been found – yet.

“This will be the first time a sponge fossil has been found from prior the Cambrian, and not just prior that, but much earlier – that’s the most exciting,” Cardenas said, adding that the research appears to confirm molecular clock estimates.

Fossil evidence is scanty prior the Cambrian, when animals first developed solid skeletons, exoskeletons, and shells, which are likely to be preserved.

“These types of fossils belong to more complicated fauna – it is clear that there must be a backward history” for simpler animals like sponges that appeared first, said study author Turner, who works at Canada’s Laurentian University.

Dating 890 million years ago is significant because if the identification of sponges is confirmed, it shows that the first animals evolved prior the time when oxygen in the atmosphere and oceans reached a level that scientists thought was necessary for animal life. However, recent research shows that some sponges can survive with little oxygen.

“Everything on Earth has an ancestor. The first evidence of animal life has forever been expected to be little and cryptic, which is very correct evidence,” said Roger Simmons, a geologist at MIT, who was not involved in the research.

There is certainly very little scientific consensus or certainty about anything dating back a billion years, so other researchers will likely persevere to examine and discuss Turner’s findings.

“I think she has a very powerful case. I think this is very worthy of publication — it puts the evidence for others to take into account,” said David Boetger, a paleobiologist at the University of Southern California, who was not involved in the research.



Referensi: www.latimes.com

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