An international study reveals the secrets of the first great mass extinction on Earth

The Late Ordovician mass extinction lasted for a significant period of time, with estimates ranging from less than half a million years to nearly two million years.

These extinctions are called the "Five Great Events", and they occurred during a certain geological period of time in which at least 3 quarters of all species on Earth faced extinction. Researchers believe we are currently in the sixth extinction as a result of global warming and climate change.

On November 1, Nature Geoscience published a paper that explores the causes of the Late Ordovician mass extinction (LOME), the first or oldest of the "Five Great Events" (about 445 million years ago). During that period about 85 percent of marine species disappeared, most of which lived in shallow oceans near continents.

Ordovician era

In their new study, an international team of scientists from several universities discuss the reasons behind the late Ordovician mass extinction. Lead author Alexander Ball, of the University of California, Riverside, and his team studied the ocean environment before, during and after the extinction to determine what the event was and why it happened.

According to an official statement published on the eurekalert website, Seth Finnigan, assistant professor at the University of California, Berkeley, said, “If you had the opportunity to dive into the deep sea during the Ordovician period, you would see some familiar groups such as oysters, snails, and sponges, in addition to many Other groups that are now less diverse or completely extinct are trilobites, theropods, and the carnioids."

Zunli Lu, a professor of Earth and environmental sciences at Syracuse University, believes that the most important result of their research lies in proving that a cooler climate can also lead to lower oxygen levels in some parts of the ocean.

“For decades, most of the prevailing ideas in our field have been that global warming is the primary cause of oxygen loss from the oceans and thus impact on the viability of marine life, potentially destabilizing the entire ecosystem,” Lu says.

He added, "Increasing evidence in recent years indicates that several episodes in Earth's history have witnessed a marked decrease in oxygen levels, which was accompanied by a cold climate."

Cold climate leads to lack of oxygen

To reach the results, the researchers measured the iodine concentration in carbonate rocks, considering that the iodine concentration in carbonate rocks is an important indicator of changes in the level of oceanic oxygen in the history of the Earth.

The results of geochemical tests supported by computer models showed that there was no evidence of oxygen deficiency during the extinction event in the shallow ocean region, where most of the living creatures lived, which suggests the idea that the cold climate that occurred during the late Ordovician era coincided with other factors responsible for the great mass extinction at that time.

“We expected oxygenation to occur in the upper ocean as a kind of response to the cold climate, because atmospheric oxygen dissolves preferentially in colder waters,” Paul says. “However, we were surprised to see the prevalence of hypoxia in the lower ocean as well, given that the lack of oxygen Oxygen is generally associated with global warming caused by volcanoes, according to what is known about the history of the Earth.

The lack of oxygen in the deep sea is attributed to the circulation of sea water through the global oceans. The main point to bear in mind, Ball says, is that ocean circulation is a very important component of the climate system.

The results of computer models have shown that a colder climate can alter the ocean circulation pattern, impeding the flow of oxygen-rich water from shallow water regions to the ocean depths.

Sixth Extinction

The researchers explained that the late Ordovician mass extinction lasted for a significant period of time, with estimates ranging from less than half a million to nearly two million years, in contrast to the rapid mass extinction that occurred in the third Cretaceous, when dinosaurs and other species died suddenly about about two million years ago. 65 million years.

This age was characterized by the abundance of rock deposits consisting of calcite or calcium carbonate that accumulated at the bottom of the oceans.

Discovering the root cause of the Earth's mass extinction has long been a central 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 in the future.

Thus, after they were able to prove the effectiveness of temperature change as a lethal tool for killing organisms that became extinct at the time, the researchers hope that in their upcoming research they will be able to provide more robust evidence to confirm their innovative hypothesis, warning that we are now grading towards the sixth extinction with accelerating climate change events.