Evolution: very early eukaryote fossils (Evolution)

by David Turell , Tuesday, November 07, 2023, 20:03 (171 days ago) @ David Turell

New find in Australia:

https://phys.org/news/2023-11-microfossils-earlier-complex-life.html

"Microfossils from Western Australia may capture a jump in the complexity of life that coincided with the rise of oxygen in Earth's atmosphere and oceans, according to an international team of scientists.

"he findings, published in the journal Geobiology, provide a rare window into the Great Oxidation Event, a time roughly 2.4 billion years ago when the oxygen concentration increased on Earth, fundamentally changing the planet's surface.

"The event is thought to have triggered a mass extinction and opened the door for the development of more complex life, but little direct evidence had existed in the fossil record before the discovery of the new microfossils, the scientists said.

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"When compared to modern organisms, the microfossils more closely resembled a type of algae than simpler prokaryotic life—organisms like bacteria, for example—that existed prior to the Great Oxidation Event, the scientists said. Algae, along with all other plants and animals, are eukaryotes, more complex life whose cells have a membrane-bound nucleus.

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"'The microfossils have a remarkable similarity to a modern family called Volvocaceae," Barlow said. "This hints at the fossil being possibly an early eukaryotic fossil. That's a big claim, and something that needs more work, but it raises an exciting question that the community can build on and test."

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"The scientists analyzed the chemical makeup and carbon isotopic composition of the microfossils and determined the carbon was created by living organisms, confirming that the structures were indeed biologic fossils. They also uncovered insights into the habitat, reproduction and metabolism of the microorganisms.

"Barlow compared the samples to microfossils from before the Great Oxidation Event and could not find comparable organisms. The microfossils she found were larger and featured more complex cellular arrangements, she said.

"'The record seems to reveal a burst of life—there's an increase in diversity and complexity of this fossilized life that we are finding," Barlow said.

"Compared to modern organisms, Barlow said, the microfossils have explicit similarities with algal colonies, including in the shape, size and distribution of both the colony and individual cells and membranes around both cell and colony.

"'They have a remarkable similarity and so, by that way of comparison, we could say these fossils were relatively complex," Barlow said. "There is nothing like them in the fossil record, and yet, they have quite striking similarities to modern algae."

"The findings have implications for both how long it took complex life to form on early Earth—the earliest, uncontroversial evidence of life is 3.5 billion years old—and what the search for life elsewhere in the solar system may reveal, the scientists said."

Comment: This sudden burst of eukaryotes 2.4 billion years ago produces another gap in evolution from Archaea to this group. Just like the Cambrian gap, no precursors. Perhaps such forms can be found.