New microfossils suggest early emergence of complex life

Microfossils from Western Australia may capture a leap in the complexity of life that coincided with an increase in oxygen in Earth’s atmosphere and oceans, an international team of scientists says.

The survey results were published in a magazine geobiology, This provides a rare window into the Great Oxidation Event about 2.4 billion years ago, when oxygen concentrations on Earth increased and the planet’s surface fundamentally changed.

This event is thought to have caused a mass extinction and opened the door to the development of more complex life, but until the discovery of new microfossils, little direct evidence existed in the fossil record. said the scientists.

“What we show is the first direct evidence linking environmental change during the Great Oxidation Event to the increase in complexity of life,” said corresponding author Erica Barlow, an affiliated research professor in the Department of Earth Sciences at Penn State. he said. “This is a hypothesis, but we haven’t been able to test it because the fossil record is so sparse.”

When compared to modern organisms, the microfossils more closely resembled a type of algae than the simple prokaryotes (organisms such as bacteria) that existed before the Great Oxidation Event, the scientists said. Algae, like all other plants and animals, are eukaryotes and are more complex life forms whose cells have a nucleus surrounded by a membrane.

More research is needed to determine whether the microfossils were left behind by eukaryotes, but the possibility could have significant implications, the scientists said. That would set back the known eukaryotic microfossil record by 750 million years.

“The microfossils have striking similarities to a modern family called Bolbocaidae,” Barlow said. “This suggests that this fossil may be that of an early eukaryote. This is a big claim and requires further research, but there are interesting questions the community can test based on it. cause.”

Barlow discovered the fossil-bearing rocks while doing undergraduate research at the University of New South Wales (USNW) in Australia, and his current research was carried out as part of his doctoral research at UNSW and then at Penn State University. I went there while conducting research as a researcher.

“These particular fossils are surprisingly well preserved, allowing us to study their combined morphology, composition, and complexity,” said Penn State professor of geosciences and co-author of the study. said Christopher House. “These results provide important clues about changes in the biosphere billions of years ago.”

Scientists analyzed the chemical and carbon isotopic composition of the microfossil and determined that the carbon was produced by living organisms, confirming that the structure was indeed a living fossil. They also revealed insights into microbial habitat, reproduction, and metabolism.

Barlow compared the sample to microfossils from before the Great Oxidation Event, but found no comparable organisms. The microfossils she discovered were larger and featured more complex cell arrangements, she said.

“This record seems to reveal an explosion of life. The diversity and complexity of this fossilized life that we are discovering is increasing,” Barlow said.

Compared to modern organisms, Barlow said microfossils have clear similarities to algal colonies, including the shape, size and distribution of the colonies and individual cells, and the membranes surrounding the cells and colonies.

“They have striking similarities, so when you compare them that way, you could say these fossils are relatively complex,” Barlow said. “Although there is nothing like them in the fossil record, they nevertheless have a very striking similarity to modern algae.”

The discovery raises questions about how long it took for complex life to form on early Earth (the earliest incontrovertible evidence for life is 3.5 billion years ago) and the solar system. The scientists said this will both affect what the search for life elsewhere reveals.

“When you find fossils this large and complex so early in the history of life on Earth, I think it raises certain questions. If life is found elsewhere, it’s probably just bacteria. It may not be a sexual prokaryote,” Barlow said. . “Maybe there’s something more complex preserved. Even if it’s still microscopic, it could be something slightly higher order.”