Monday, January 24

‘Wavy’ Fossils Found in Canada May Be the Oldest Known Sign of Animal Life | Fossils


The intricate patterns of tubular structures discovered in giant ancient reefs may be the remains of prehistoric horny sponges and the oldest known fossils of animal life on Earth.

The researchers found the unusual features in vast reefs that were built by bacteria 890 million years ago and then pushed upward by geological processes to form part of the Mackenzie Mountains in northwestern Canada.

Examined under a microscope, a small number of rock samples revealed tubules about half the width of a human hair that branch and reconnect to form 3D structures that are strikingly similar to those seen in fossils of the bath sponges.

“Initially, when you look at these features, they look like a lot of wiggling, but when you try to follow each of the threads, you realize that even in thin sections they form complicated 3D meshes,” said Laurentian University Professor Elizabeth Turner . in Sudbury, Ontario.

Professor Elizabeth Turner in North Baffin Island, Nunavut
Professor Elizabeth Turner in North Baffin Island, Nunavut. Photography: C Gilbert

“Thanks to the wonderful work of others, younger examples of the same microstructures have been found in sponge body fossils and these structures have been compared to the skeletons of a variety of keratose or horny sponges,” he added.

While modern reefs are built by corals and algae, in Earth’s distant past, communities of photosynthetic cyanobacteria created huge carbonate reefs that are many kilometers wide and hundreds of meters thick.

Professor Turner first saw the strange tubules in a handful of thin sections of rock that she gathered as a PhD student during fieldwork at the site. Two decades later, he has built the collection and discovered more examples of the features in the rocks.

Writing in the diary NatureTurner describes how the fossils may have formed when putative sponges, which are a few millimeters to one centimeter wide, mineralized. Soft tissue is the first to fossilize and encloses the 3D network of collagen-like fibers that make up the sponge’s skeleton. Over time, these skeletal fibers break down, leaving hollow tubules that fill with calcite crystals.

If the structures are confirmed as the earliest sponge fossils, they would predate the next oldest undisputed sponge fossils by about 350 million years.

According to previous studies, sponges are some of the earliest animals on Earth, emerging during the early Neoproterozoic era between one and a half billion years ago. However, the exact moment is uncertain. Other research suggests that oxygen levels were too low for animals to thrive until they spiked in the neoproterozoic oxygenation event between 800 and 540 million years ago.

But even on an oxygen-starved Earth, the first sponges may have found a way to survive in the nooks and crannies of microbial reefs if the photosynthetic bacteria that suffocated the reefs released enough oxygen into the water. “These possible sponges, or whatever they were, lived on a reef that was an oxygen factory, it was nirvana,” said Professor Turner. As food, they could have consumed the polysaccharide slime that was shed from the microbial mats into the surrounding ocean.

“If I am correct about the interpretation of this material, then it is possible that the first animals did not have the same oxygen requirements that we have assumed until now. It is possible that the first sponges emerged some time ago, and certainly 890 million years ago, living in a world comparatively low in oxygen, but the most complicated animals had to wait a while, “he added.

Much more work is now needed to see if other rocks of a similar age contain traces of early animal life. “We have to approach it with a much more open mind,” said Professor Turner. “We have to think about what to expect from the first animals. Anything that we consider animal can be too complicated. We want to find something that expresses the essence of animals, without being too conspicuously familiar. “


www.theguardian.com

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