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Dating pinpoints volcanoes that killed half of species, split continents

AFP-JIJI

New techniques for dating rocks have helped narrow the time frame of a chain of massive volcanic eruptions that wiped out half of the world’s species 200 million years ago, a study said Thursday.

The result is the most precise date yet — 201,564,000 years ago — for the event, which is known as the Triassic-Jurassic extinction event, said the study, published in the journal Science. The event was the fourth mass extinction in the history of our planet.

The eruptions “had to be a hell of an event,” said coauthor Dennis Kent, an expert on paleomagnetism at Columbia University’s Lamont-Doherty Earth Observatory.

They may offer a historic parallel to the human-caused climate change happening today, by showing how sharp increases in carbon dioxide can outpace vulnerable species’ ability to adapt, researchers said.

The new analysis narrows the estimated date from its previous range of up to 3 million years to just 20,000 years at most — a blink of an eye in geological terms.

The eruptions caused an already hot Earth to become even more stifling, killing off plants and animals and making way for the age of the dinosaurs — before they, too, were eventually obliterated some 65 million years ago, possibly by another volcanic event combined with a devastating meteor strike.

Volcanoes roiled the Earth at a time when most land was united in one big continent, spewing out roughly 10 million cu. km of lava. Over time, the eruptions split the supercontinent apart and led to the creation of the Atlantic Ocean.

For the study, scientists analyzed rock samples from Nova Scotia, Morocco and outside New York City, all of which came from this once-united landmass, known as the Central Atlantic Magmatic Province.

An analysis of the decay of uranium isotopes in the basalt, a type of rock left by the eruptions, offered researchers more precise dates.

The eruption in Morocco was the earliest, followed by Nova Scotia about 3,000 years later and New Jersey 13,000 years later.

Sediments that lie below that time hold fossils from the Triassic era. Above that layer, they disappear, the study said.

Some of the lost creatures include fish resembling eels, called conodonts, early crocodiles and tree lizards.

“In some ways, the end Triassic extinction is analogous to today,” said lead author Terrence Blackburn, who carried out the study while at the Massachusetts Institute of Technology but is now with the Carnegie Institution.

“It may have operated on a similar time scale. Much insight on the possible future impact of doubling atmospheric carbon dioxide on global temperatures, ocean acidity and life on earth may be gained by studying the geologic record.”