Scientist finds new evidence in Australian rocks
A Sydney scientist has uncovered critical evidence about the earliest known complex life forms in the universe, isolated from slices of Australian mudstone that preserved the bodies of primitive marine organisms.
Microscopic creatures, 1.7 billion years old, are among our oldest ancestors; precursors that gave rise to all multicellular life, from fungi to velociraptors, humans, insects, trees, and toucans.
Geobiologist Dr Max Lechte sought to determine where and why cells became complex and gave rise to life as we know it. It’s an ancient mystery that could help alien-hunting astrobiologists decide which planets to train their telescopes on.
Life on Earth was dominated by primitive bacteria for almost four billion years.
“Why didn’t life stay simple?” said Lechte. “Why did we eventually evolve into more complex forms and eventually into animals and intelligent life, including us?”
Lechte, from the University of Sydney, explored ancient rocks in the McArthur and Birrindudu basins in the Northern Territory to answer these questions in a new way. Nature paper.
‘Why didn’t life stay simple? ‘Why did we eventually evolve into more complex forms and eventually into animals and intelligent life, including us?’
Geobiologist Dr Max Lechte
The landscape of rocky canyons and red soil was once an inland sea. Microscopic organisms lived in the waters, died and sank into the mud of the seafloor, which hardened into rock.
By dissolving pieces of this rock in an acid that preserves organic material, Lechte’s co-author, Leigh Anne Riedman of the University of California, San Francisco, uncovered 12,000 fossil microbes.
Some were primitive spheres, but others were more elaborate, with protruding appendages and plates or wrinkled surfaces like whorls of fingerprints. These were ancient “eukaryotes,” the earliest versions of a new, more complex form of life that would give rise to all plants, animals, and fungi.
“These are the earliest microbial ancestors that we can see,” Lechte said.
Lechte analyzed the chemistry of the rocks. He was looking for iron, which reacts easily with oxygen (think of an exposed nail rusting with air) and reveals details about ancient oxygen levels.
The team discovered that eukaryotes grow only in shallow, oxygenated coastal waters. In deeper waters where oxygen did not reach them, they found only simple single-celled bacteria.
At that time, long before the emergence of plants, the only life forms that pumped oxygen were cyanobacteria. Oxygen levels hovered at 1 percent of current levels, and the gas dissolved only in the shallowest surfaces of the sea.
Lechte’s results show that our early ancestors were confined to these oxygen-limited pockets for about a billion years, when high gas levels released them into new habitats, resulting in the emergence of algae, fungi, sea sponges and jellyfish.
Oxygen accelerates the conversion of organic carbon into energy, like a pair of bellows blowing coals into a roaring fire. But it can also be toxic and damage cells through oxidation.
Harnessing oxygen was an evolutionary trade-off between taking advantage of a powerful new fuel and learning to repair oxidative damage: the job of a complex organism.
Lechte argues that ancient creatures living in oxygen-rich habitats must have acquired mitochondria, the “powerhouse” structure that converts oxygen into energy in all eukaryotic cells, including ours.
“This is important because this determines the minimum date for when mitochondria were acquired,” says Lechte. “We know it must have happened 1.7 billion years ago.”
The findings support the idea that the rise of mitochondria was a major turning point in the transition from a planet filled with slimy microbial layers to the extraordinary biodiversity we see today.
Latest research on the subject origin of mitochondria He focused on the possible role of Asgard archaea (a microbe called the celestial citadel of the gods in Norse mythology) that lived alongside the ancient stromatolites of Western Australia.
Stromatolites are the oldest form of bacterial life; They are 3.5 billion-year-old rocky structures built by cyanobacteria. Last month, scientists revealed that an Asgard microbe from Shark Bay stromatolites interacted with a bacterium through tube-like structures known as nanotubes.
A long-accepted biological theory is that such interaction mitochondria formationif one germ swallows another. The partnership between Asgardian archaea and bacteria may be a sign of the missing link between single-celled life and the types of mitochondria-containing organisms found in Northern Territory rocks.
Brendan Burns, an associate professor at the University of NSW and part of the stromatolite research team, said the new Nature The article was interesting, but noted that fossils offer limited information about an organism’s metabolic lifestyle.
“It may be difficult to tell from this study whether early eukaryotes required oxygen or simply tolerated oxygen,” he said. Organisms may have just learned to tolerate toxic oxygen rather than use it.
Knowing how life formed in deep time, when Earth was an extreme and alien place, helps the search for extraterrestrial life, Lechte said.
“Before we speculate about what conditions are good for life on other planets, it’s really important to understand how life got here on our planet.”
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Angus Dalton is science correspondent for The Sydney Morning Herald.Connect with: X or email.
