Uncover the amazing secrets of Earth’s first great mass extinction

A team of researchers has published a new study that explores the cause of the mass extinction of the Ordovician.

We all know that dinosaurs became extinct due to mass extinction. But did you know there are other mass extinctions? There are five critical mass extinctions, known as the “Big Five,” in which at least three-quarters of all species around Earth were threatened with extinction within a geological period. With current trends in global warming and climate change, many researchers now believe we could be ranked sixth.

Uncovering the root cause of Earth’s mass extinction has long been a hot topic for scientists, because understanding the environmental conditions that wiped out the majority of species in the past can help prevent a similar event from happening again in the future.

A team of scientists from the Department of Earth and Environmental Sciences at Syracuse University University of California, Berkeley The University of California, Riverside, University of Bourgogne-French Comte, University of New Mexico, University of Ottawa, University of Science and Technology of China, and Stanford University recently co-authored research exploring the Late Ordovician Mass Extinction (LOME), the first or oldest of the “Big Five (before 445 million years ago). year). About). About 85% of marine species, most of which lived in shallow oceans near continents, became extinct during this time.

Detailed images of fossils from the Ordovician outcrop of Anticosti Island, Quebec, Canada. Credit: André Desrochers, University of Ottawa

Lead author Alexander Paul of the University of California Riverside (now a postdoctoral researcher at the University of Bourgogne-Franch-Comte in Dijon, France) and his co-authors studied the ocean environment before, during and after the extinction to determine what the event looked like. Fermented and lit. The results of their study were published in the journal natural earth sciences Today (November 1, 2021).

To paint a picture of the ocean ecosystem during the Ordovician period, mass extinction expert Seth Finnegan, associate professor at UC Berkeley, said the seas teemed with biodiversity. The oceans contained some of the oldest corals created by animals, but they lack an abundance of vertebrates.

“If you had gone diving in the Ordovician Sea, you would have seen familiar groups such as oysters, snails, and sponges, but also many other groups that are now less diverse or completely extinct such as trilobites, theropods, and sponges,” Finnegan said.

Unlike a rapid mass extinction, such as chalkyThe third extinction occurred when dinosaurs and other species died suddenly about 65.5 million years ago, Finnegan says.

Ordovician outcrop fossils

Detailed images of fossils from the Ordovician outcrop of Anticosti Island, Quebec, Canada. Credit: André Desrochers, University of Ottawa

One of the main debates about LOME is whether the lack of oxygen in seawater caused the mass extinction of this period. To investigate this question, the team combined geochemical testing with numerical simulations and computer modeling.

Zunli Lu, a professor of Earth and Environmental Sciences at Syracuse University, and his students measured the concentration of iodine in carbonate rocks from this period and made important discoveries about oxygen levels in various ocean depths. The concentration of iodine in carbonate rocks serves as an indicator of changes in the level of ocean oxygen in Earth’s history.

Their data, along with computer simulations, indicated that there was no evidence of hypoxia – or hypoxia – at the extinction in the shallow ocean animal habitat where most organisms lived, implying that climate cooling occurred towards the end of the Ordovician period with factors that from Likely to be responsible for LOME.

On the flip side, there is evidence that hypoxia in the deep ocean is spreading at the same time, a mystery that cannot be explained by the classical model of ocean oxygen, explains climate modeling expert Alexander Ball.

“Oxygenation in the upper ocean was expected in response to the cooling, as atmospheric oxygen preferentially dissolves in colder waters,” Ball explains. “However, we were surprised to see the prevalence of hypoxia in the lower ocean since hypoxia in Earth’s history has generally been associated with global warming caused by volcanoes.”

They attribute the lack of oxygen in deep waters to the circulation of seawater across the world’s oceans. The main point to keep in mind, Ball says, is that ocean circulation is a very important component of the climate system.

He was part of a team led by lead designer Andy Ridgewell, a professor at the University of California Riverside, whose results from computer modeling showed that climate cooling likely changed the ocean circulation pattern, stopping the flow of oxygen-rich water in shallow seas to the deep ocean.

Recognizing that climate cooling can also lower oxygen levels in parts of the ocean, Lu says, is a key part of their study.

Lu explains: “For decades, the dominant school of thought in our field has been that global warming is causing the oceans to lose oxygen, thus affecting the viability of marine life, destabilizing the entire ecosystem.” Evidence points to several periods in Earth’s history where oxygen levels also decreased in colder climates.”

While the causes of the late Ordovician extinction are not fully agreed upon and will not be agreed upon for some time, the team’s study rules out oxygen changes as an explanation for this extinction and adds new data that reinforces temperature change as a destruction mechanism for LOMÉ.

Buhl hopes that with better climate data and more complex numerical models, they will be able to provide a stronger representation of the factors that may have led to the late Ordovician mass extinction.

Reference: “Vertical separation in late Ordovician hypoxia due to reorganization of ocean circulation” by Alexander Ball, Zunli Lu, Wani Lu, Richard J. Ridgewell, 1 November 2021, Available here. natural earth sciences.
DOI: 10.1038 / s41561-021-00843-9

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