The great mass extinction event – popularly called the Great Dying – that wiped out nearly 70% of Earth’s land animals 252 million years ago took place at different times in history on land and at sea , according to one new research on fossils from South Africa and Australia and collected by the journal Nature Communications . The lag between land extinction in the southern hemisphere and marine extinction in the northern hemisphere suggests different causes.
The work, carried out by scientists from Colby College and the University of California at Berkeley (USA), found new ages for the fossilized vertebrates that lived just after the disappearance of the fauna that dominated the late Permian epoch ago 299 to 251 million years ago.
” Most scientists thought that the land collapse began at the same time as the marine collapse, and that it occurred at the same time in the southern hemisphere and in the northern hemisphere ,” said paleobotanist Cindy Looy of the University of California. “The fact that the large changes were not synchronous in the northern and southern hemispheres has a large effect on the hypotheses of what caused the extinction. An ocean extinction, per se , does not have to have the same cause or mechanism as an extinction on land. “
Resetting the timeline
According to paleontologists and sedimentologists, changes in the ecosystem during this mass extinction event in which most species disappeared due to a series of volcanic eruptions that released harmful greenhouse gases, began hundreds of thousands of years earlier in on land than in the sea.
Thus, just over 250 million years ago, when the dinosaurs were just in their earliest phase, the Earth was going through an incredibly difficult time. There are signs that tectonic activity near what is now Siberia (Russia) generated pulses of eruptions that coincided with the loss of approximately 90% of all species, based on chemical changes in the geological record, as well as the rapid decline of relatively common fossils and animals, such as Daptocephalus, and increased bones of opportunistic species, such as Lystrosaurus, which excelled in the Lower Triassic. All of them now extinct.
The subsequent marine extinction, in which nearly 95% of ocean species disappeared, may have occurred in the time span of tens of thousands of years later. In the ocean, the final Permian extinction is perhaps best associated with the disappearance of the trilobites.
Dating with Uranium-Lead
Experts estimated the ages of zircon mineral crystals in a fairly well-preserved volcanic ash deposit in the Karoo Basin of South Africa (which was part of the Gondwana landmass, the southern half of the supercontinent known as Pangea that would later separate into current continents). They found that sediments several meters above the dated layer were devoid of pollen from Glossopteris (a late Paleozoic shrub), suggesting that these seed ferns, which used to dominate the late Permian Gondwana flora, became extinct around that time. At 252.24 million years old, zircons, microscopic silicate crystals that form in rising magma within volcanoes and are thrown into the atmosphere during eruptions, are 300,000 years older than the dates previously noted for the Permian boundary. -Triassic (PT) in China, confirming that life on earth was already beginning to fade shortly after being deposited.
“Our new zircon date shows that the base of the Lystrosaurus zone predates marine extinction by several hundred thousand years, similar to the pattern in Australia,” Looy said. “This means that both the floral and faunal rotation in Gondwana are out of sync with the marine biotic crisis in the northern hemisphere.”
Was the Permian extinction event much slower than we imagined? It seems.
“For some years now, we have known that, in contrast to the marine mass extinction, the disturbance pulses of life on earth continued into the Triassic period. But that the fact that the beginning of terrestrial renewal occurred long before than the navy, it was a surprise. “
Referencia: Robert A. Gastaldo et al. The base of the Lystrosaurus Assemblage Zone, Karoo Basin, predates the end-Permian marine extinction, Nature Communications (2020). DOI: 10.1038/s41467-020-15243-7
