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Why does it take life 10 million years to recover from a mass extinction?

Regaining species diversity after mass extinction takes about 10 million years. The calculation, made two decades ago, was based on the study of the largest of the five great known extinctions: the Permian-Triassic, which 250 million years ago killed 90 percent of the planet’s species. Its cause or causes are not clear: the impact of a meteorite, a set of huge volcanic eruptions, climate change, the destruction of the ozone layer, a conjunction of several …

Scientists thought that this deadline is due to a sum of environmental factors. However, a team of researchers from the University of Texas at Austin has just published in the journal Nature Ecology & Evolution a work that they claim responds to the characteristics of evolution. Mass extinctions annihilate the entire repertoire of evolutionary adaptations accumulated over eons (periods of hundreds of millions of years) , and developing others that allow the generation of new species at a rate comparable to that before the catastrophe takes ten million years.

What is the new hypothesis based on?

In the analysis of fossils of foraminifera (a type of plankton) dated before and after the most famous mass extinction, not the most lethal: the one that 66 million years ago wiped out all dinosaurs and two-thirds of species, although not with small mammals, which is why you are reading this. The most widely accepted theory about the origin of the phenomenon is the impact with the Earth of a large asteroid , although recent research suggests that a series of huge volcanic eruptions contributed decisively.

Scientists at the University of Texas have compared the type diversity of these organisms with their individual physical complexity, and have observed that it was not until the latter factor was sufficiently developed that diversification of foraminifera species began. That is, it takes a certain level of complexity in an organism before it gives rise to different species.

The fossil record has revealed that the diversity of the foraminifera declined dramatically after the impact of the famous asteroid, and that their surviving species quickly occupied the ecological niches that had become available. But they did not reach a biodiversity similar to that prior to extinction until after 10 million years. Foraminifera fossils abound in marine sediments around the world, allowing specialists to determine their evolution over long periods of time, since there are very few intervals lacking specimens.

A warning of what can happen

The speed of recovery of this class of plankton after a mass extinction coincides with that calculated for the rest of the species 20 years ago, which adds strength to the investigation. One of its main authors, the geophysicist Christopher Lowery, thinks that “these same processes are present in the rest of mass extinctions. In my opinion, it is the rhythm of evolution itself that explains the limits on the speed for biodiversity to fully recover after a global catastrophe ” .

Lowery and his colleagues point out that the 66-million-year-old asteroid impact is the only event in Earth’s history that caused a change faster than present global warming, so they believe their work may provide clues to a possible recovery of biodiversity after major human-caused extinctions. In fact, some scientists think that the sixth great extinction has already begun, driven by our species.

Illustration (John Maisano / University of Texas at Austin): Representation of the seabed after the mass extinction that wiped out the dinosaurs. All three hairy forms are surviving plankton species. The geometric organism is a kind of algae.

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