Evrim Yazgin
Cosmos science journalist
A study of ancient volcanism shows that dinosaurs took over the Earth about 200 million years ago because they thrived in the cold.
This challenges long-standing theories that heating of the Earth was the principal impact on evolution of the dinosaurs.
The earliest dinosaurs evolved about 230–240 million years ago during the Triassic period (252–201 million years ago). They were mostly small, two-legged carnivores. But they still lived under the shadow of the dominant land animals at the time – the synapsids – which would later evolve into the first mammals.
It wasn’t until the mass extinction at the end of the Triassic period that dinosaurs had took their chance and became the most successful group of land animals. After the Triassic came the Jurassic period (201–145 million years ago) and the rest is history.
The new research, published in the Proceedings of the National Academy of Sciences, looked at geological records from the End Triassic Extinction – one of the 5 great mass extinctions in Earth’s history.
About 75% of all species suddenly disappeared at the end of the Triassic.
The wipeout coincided with the massive volcanic eruptions that split apart the ancient supercontinent Pangea. Over 600,000 years, millions of cubit kilometres of lava spewed out of the Earth and separated Pangea into Laurasia (now Europe, Asia, North America and Greenland) and Gondwanaland (Antarctica, Africa, South America, India, Madagascar and Australia).
The exact mechanisms behind the End Triassic Extinction have long been debated.
It was widely believed that carbon dioxide released by the eruptions built up over thousands of years causing a greenhouse effect, raising temperatures and acidifying the oceans.
But the new research says the opposite: cold, not high heat, is what lead to the mass extinction.
The study suggests that the volcanism was made up of short, intense pulses lasting less than a century each, instead of taking hundreds of thousands of years.
In this condensed timeframe, light from the sun is reflected by sulphates back into space cooling the planet and freezing its inhabitants.
“Carbon dioxide and sulphates act not just in opposite ways, but opposite time frames,” says lead author Dennis Kent of the Columbia Climate School in New York. “It takes a long time for carbon dioxide to build up and heat things, but the effect of sulphates is pretty much instant. These events happened in the span of a lifetime.”
Kent and colleagues produced a study in 2013 which tied the Triassic-Jurassic extinction to the eruption of the Central Atlantic Magmatic Province (CAMP) 201,564,000 years ago, give or take a few thousand years.
Their latest work compared CAMP deposits from Morocco, the Bay of Fundy in eastern Canada/US, and the Newark Basin in New Jersey, US.
Studying the magnetic properties of the rocks which would have been affected by Earth’s drifting magnetic pole, they determined that the CAMP lava deposits were spread over just 40,000 years.
Because the magnetic particles in individual rock layers were aligned in a single direction, they could tell that they were laid down in pulses lasting less than 100 years.
They liken the fast release of sulphates from these pulsed lava eruptions to the 1783 eruption of Iceland’s Laki volcano which caused widespread crop failures.
“The magnitude of the environmental effects are related to how concentrated the events are,” said study coauthor Paul Olsen, a palaeontologist at Columbia. “Small events spread out over [tens of thousands of years] produce much less of an effect than the same total volume of volcanism concentrated in less than a century. The overarching implication being that the CAMP lavas represent extraordinarily concentrated events.”
Previous studies have also suggested that, contrary to previous theories, it was the early development of feathers in dinosaurs which saw them adapt faster to the cold and proliferate after the End Triassic Extinction.
