Double catastrophe killed dinosaurs, says study

A team of geologists have uncovered evidence that an asteroid impact on Earth 66 million years ago accelerated huge Indian volcanic eruptions – known as the Deccan Traps – for hundreds of thousands of years. The researchers suggest that, together, these planet-wide catastrophes led to the extinction of many land and marine animals, including the dinosaurs.

The researchers found that the eruptions accelerated within 50,000 years of the asteroid impact and were likely reignited by the impact, which may have generated magnitude 9 earthquakes or stronger everywhere on Earth. The study results appear in the October 2 issue of the journal Science.

For 35 years, paleontologists and geologists have debated the role that these two global events – the asteroid impact and the Deccan Traps eruptions – played in the last mass extinction. One side claims the eruptions were irrelevant, and the other side claims the impact was a blip in a long-term die-off.

The new evidence includes what the researcher say are the most accurate dates yet for the volcanic eruptions before and after the impact. The new dates show that the Deccan Traps lava flows, which at the time were erupting at a slower pace, doubled in output within 50,000 years of the asteroid or comet impact that is thought to have initiated the last mass extinction on Earth.

Both the impact and the volcanism would have blanketed the planet with dust and noxious fumes, say the scientists, drastically changing the climate and sending many species to an early grave.

Lead researcher Paul Renne is a University of California Berkeley professor-in-residence of earth and planetary science and director of the Berkeley Geochronology Center. Renne said:

Based on our dating of the lavas, we can be pretty certain that the volcanism and the impact occurred within 50,000 years of the extinction, so it becomes somewhat artificial to distinguish between them as killing mechanisms: both phenomena were clearly at work at the same time.

It is going to be basically impossible to ascribe actual atmospheric effects to one or the other. They both happened at the same time.

Since 1980, when scientists discovered evidence of a comet or asteroid impact on Earth 66 million years ago, scientists have argued about whether the impact was the cause of the mass extinction that occurred at the same time, the end of the Cretaceous period, or the KT boundary. Some argued that the huge volcanic eruptions in India known as the Deccan Traps, which occurred around the same time, were the main culprit in the extinctions. Others insisted the death knell had been the impact, which left behind a large crater dubbed Chicxulub off Mexico’s Yucatan peninsula, and viewed the Deccan Traps eruptions as a minor sideshow.

The geologists argue that the impact abruptly changed the volcanoes’ plumbing system, which produced major changes in the chemistry and frequency of the eruptions. After this change, long-term volcanic eruptions likely delayed recovery of life for 500,000 years after the KT boundary, the term for the end of the Cretaceous and the beginning of the Tertiary period when large land animals and many small sea creatures disappeared from the fossil record. Renne said:

The biodiversity and chemical signature of the ocean took about half a million years to really recover after the KT boundary, which is about how long the accelerated volcanism lasted. We are proposing that the volcanism unleashed and accelerated right at the KT boundary suppressed the recovery until the volcanoes waned.

In the Science paper, the scientists describe major changes in the Deccan Traps volcanism, which was probably “bubbling along happily, continuously and relatively slowly” before the extinction, Renne said. After the impact, the eruption rate more than doubled and the volcanism became more punctuated, with more voluminous lava flows interspersed with long periods of quiet. This is consistent with a change in the underground plumbing feeding the flows, he said: Smaller magma chambers before the impact became larger, which means they took longer to fill but spewed more lava when they did erupt. Renne said:

At the KT boundary, we see major changes in the volcanic system of the Deccan Traps, in terms of the rate at which eruptions were happening, the size of the eruptions, the volume of the eruptions and some aspects of the chemistry of the eruptions, which speaks to the actual processes by which the magmas were generated … Our data don’t conclusively prove that the impact caused these changes, but the connection looks increasingly clear.

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Bottom line: In a paper in the October 2, 2015 issue of Science, geologists describe evidence that suggest that an asteroid impact on Earth 66 million years ago accelerated the Indian Deccan Trap volcanic eruptions for hundreds of thousands of years. The researchers suggest that, together, these planet-wide catastrophes led to the extinction of many land and marine animals, including the dinosaurs.

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