It was during the Jurassic period that the speciation of flora and fauna was actively going on, and at the end of the period, not only giant dinosaurs appeared on land, but also the first rodents and ancestors of modern birds.
However, it was in the Jurassic era that the fauna of the planet was fairly thinned out by several mass extinctions. The Haaretz portal writes about a study dedicated to finding their causes.
According to one theory, the cause of the extinctions was the active activity of volcanoes, which lasted about a million years during the Jurassic in the southern part of the Gondwana supercontinent. However, this fact correlates with only one mass extinction, called the Toarcian, which occurred about 183 million years ago. And it can’t explain the other Jurassic extinctions.
Now, in a new study published in the journal Gondwana Research, scientists say they have been able to date multiple episodes of volcanic activity, each lasting millions of years, during the Early and Middle Jurassic, between 186 million and 178 million years ago. This could explain multiple mass extinction events during the Jurassic period, the researchers say.
These volcanic events occurred in one part of the Gondwana supercontinent, which has since split into modern continents. Today, lands with the remnants of this Jurassic volcanic chaos lie in southern Africa, in Australia and Antarctica – in the Karoo province and in the territory of Ferrara.
The ages of igneous rocks from these areas have been dated at the Nordsim laboratory in Stockholm using the “uranium-lead method” on samples of tiny zircon crystals contained in volcanic rocks.
“Our results strongly support the theory that episodic magmatism in the Karoo Province may have been responsible for recurring Jurassic ecological and biological crises,” said study lead author Arto Luttinen of the Finnish Museum of Natural History.
However, what caused this volcanic activity is not entirely clear – it is possible, according to a 2017 theory, that the cause of the eruptions was that a tectonic plate called the Phoenix slid under southern Gondwana.
It was formerly thought that Karoo volcanism was dated to that narrow phase of a million years which coincided with the Toarcian mass extinction. Now Luttinen and his colleagues have proven that the Karoo-Ferrara volcanism lasted millions of years and could have been the cause of numerous extinctions during the Jurassic.