Volcano-induced die-off paved way for dinosaurs, study suggests

More than 200 million years ago, toothy crocodile-like creatures stalked a hot, dry mega-continent while squid-like mollusks with spiral shells drifted in the surrounding ocean. Then, in what passes for an instant in geologic time, they vanished - making way for the age of the dinosaurs.

How 50 per cent of terrestrial vertebrates and an even larger share of marine life died off in the late Triassic period has become more clear from new research published online on Thursday in the journal Science.

The work lends greater validity to the theory that a massive volcanic event tore apart that continent and blanketed earth's atmosphere, turning the ocean acidic and snuffing out animals that could not adapt. That geologic event, which created the Atlantic Ocean, ushered in the biggest biological shift in the planet's history.

"It set the stage for the dinosaurs to take over, biologically," said Paul Olsen, a geologist at Columbia University's Lamont-Doherty Earth Observatory, who did much of the field work on which the study is based.

Pushed by the nascent Atlantic, the ruptured pieces of Pangea drifted off and further split, carrying the evidence of ecological collapse to such distant locales as Morocco, Nova Scotia and New Jersey.

Matching the fossil record in sedimentary rock with the dense basalt formed by the volcanic eruptions proved difficult, even with sophisticated tools of the 21st century. It was difficult to say whether the eruptions happened before the mass extinction.

Olsen and others, however, hacked rare zircon crystals from the basalt formations and measured traces of lead and uranium for radiometric dating tests. The results narrowed the margin of error in dating the lava to a mere 15,000 to 22,000 years - stunning precision for geochronology.