Most major groups of animals, including arthropods, mollusks, and worms, first appeared in the fossil record during the Cambrian explosion, 541 million years ago. But according to an article published in natureFossils of sponges from northwest Canada may be more than 350 million years old, significantly delaying the date of the first known animal on Earth.
The gross discovery causes Controversy among paleontologists, who have long wondered when the first evolution of complex animal life occurred.
Study author Elizabeth Turner, a sedimentary geologist at Laurentian University in Sudbury, Canada-. This means that there is a long history of animals that have not been well preserved.”
However, some scholars They are not convinced that the microscopic patterns in the 890-million-year-old Turner fossils suggest an ancient sponge, given the evidence presented and available in the study.
“It’s a big claim that you really have to eliminate all other possibilities – warns Rachel Wood, a geologist at the University of Edinburgh, UK, who researches fossil reefs.. Microbes, for example, produce weird and wonderful shapes. Sometimes the crystals also grow in a way that resembles the patterns made by living things. Which means that the rock samples that Turner found may not be fossils at all.”
Turner responds None of the organisms known to build reefs that existed 890 million years ago, like cyanobacteria or algae, It can explain the complex structures of your samples.
specialist collection Presumed fossils of ancient microbial reefs preserved in the rocks of Canada’s remote Northwest Territories, during his graduate studies in the 1990s.
When Turner examined the rock slices under a microscope, he saw branching networks of crystal tubes. Later I realize it These internal scaffold structures resemble modern corneal sponges and are in keeping with the expected ossification and sponge patterns, Collagen protein that forms a scaffold. “These rocks are beautiful,” he said, “but don’t expect to find anything complicated or strange about them.”
It wasn’t until the last few years when Turner noted studies describing similar structures in much smaller rocks, from a time when sponges were known to exist, which she felt confident to publish her findings. But these studies are also disputed on the grounds that they may not be actual sponge fossils.
The authors are one of these Articles They took pictures of several thin slices of their rock sample and used them to create a 3D model of the putative sponge. Wood says a similar test would have corroborated Turner’s claim.
“If Turner’s structures turn out to be sponge fossils, that would be very exciting and help us determine the initial history of animal evolution,” says David Gold, a geologist at the University of California, Davis, a topic that has been debated for decades.
but also He continues: “It is easy to find sponge-like things in the fossil record, and it is difficult to support them with other evidence. He and other researchers, for example, have supported Fossil finds indicate rock samples that contain traces of biological particles associated with sponges. “Unfortunately, given the great age and type of Turner’s rock samples, this kind of preservation isn’t really possible,” he continues.
“It is not inconceivable that sponges could have preceded the Cambrian explosion,” explained Phoebe Cohen, a geologist at Williams College in Williamstown, Massachusetts. Scientists estimate how long ago The ancestors of living animal populations varied using molecular clocks, which measure the rate of mutation in DNA and proteins over time.
Most of these estimates suggest that the last common ancestor of all animals living today evolved before the Cambrian explosion, “but not in 350 million years,” according to Cohen. However, you might be convinced that Turner’s specimens are sponge fossils if you see more evidence, including studies of how hot sponges fossilize.“.
Molecular Clock Estimates
The paleontological community is divided over whether the scarcity of precambrian animal fossils is due to creatures that rarely survived as fossils to the present day. Or because molecular clock estimates of animal origins are incorrect. Gold is convinced that sponges existed before the Cambrian, but for him, exactly how far back is a big unresolved question.
“If the ancestors of modern sponges actually lived 890 million years ago, then this means that the first animals survived very difficult conditions for life, Such as extremely low oxygen levels and periods of snowfall during which the planet’s surface almost completely freezes.
Turner argues that Sponges could have survived a low-oxygen environment by making a living in cavities and crevices in microbial reefs along with photosynthetic cyanobacteria, which release oxygen. AndSponges may also feed on organic secretions produced by bacteria. “Maybe there was a very tasty and abundant supply of ‘mucus’ for these filter-feeding organisms to feast on,” he said.
Scientists are passionate about their insights into when animal life began on Earth. “The document could reinvigorate a debate that has been simmering for decades,” Gold concludes. But I suspect that the mindset of those who have made a decision about the age of the animals will not change much.”
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