Meteor strike was 'nail in dinosaurs' coffin'

Meteor strike was 'nail in dinosaurs' coffin'

8 February 2013, by Tamera Jones

Dinosaur extinction.

Using high-precision dating techniques, scientists have discovered that ecosystems were already under critical stress, probably from the effects of massive volcanic eruptions in what is now India, which lasted for around 1.5 million years.

The international team came to their conclusions after finding the most precise dates yet for both when the dinosaurs went extinct, and when a six-mile-wide asteroid slammed into Mexico's Yucatán Peninsula at Chicxulub.

The extinction happened not 65 million years ago, but 66,043,000, while the asteroid struck up to 11,000 years earlier.

The scientists say the events were so close that it's likely the impact of the asteroid, if not completely responsible for the global extinction, at least dealt the death blow for the dinosaurs.

'The impact was clearly the final straw,' says Professor Paul Renne, director of Berkeley Geochronology Center (BGC), lead author of the study, published in Science.

The findings provide the first definitive evidence for the sequence of events that led what is known as the Cretaceous-Paleogene (K-P) mass extinction event.

'We have shown that these events are synchronous to within a gnat's eyebrow and therefore the impact clearly played a major role in extinctions, but it probably wasn't just the impact,' says Renne.

The K-P event is one of the three largest mass extinctions in 500 million years. It wiped out dinosaurs, large marine reptiles, and two thirds of all species on Earth, ultimately paving the way for mammals to rise to dominance.

But exactly what caused it is the subject of intense debate among scientists. Some blame a six-mile-wide meteor slamming into the planet. Others suggest that massive volcanic activity, which lasted for over a million years, was the likely cause. Such eruptions spewed around 1.1 million square kilometres – the size of Colombia – of basalt lava across the Deccan Traps, which would've cooled the atmosphere and caused severe acid rain, spelling the end for much of life on Earth.

'One of the main reasons for the on-going debate stems from the ambiguity around the precise dating of these events,' says Dr Darren Mark from the Scottish Universities Environmental Research Centre (SUERC) in East Kilbride, Scotland, co-author of the study.

Previous studies confuse the issue, because they put the extinction event anything from several hundred thousand years before the impact to 183,000 after it.

So Renne, Mark and researchers from Berkeley, the Netherlands and the UK collaborated to establish the most accurate date yet for both.

Renne and colleagues at Berkeley collected a series of ash samples from Haiti to figure out how long ago the impact happened. They dated it to 66,038,000 years, give or take 25,000.

Next, they dated samples of ash from the Hell Creek Formation in Montana to find out exactly when the dinosaurs went extinct. This is the site of many dinosaur fossils and is one of the best places to study the change in what was living before and after the K-T extinction. For this event, they established a date of 66,043,000 years with an error of 11,000 years.

Once they'd established a date for the extinction, they sent the same samples to SUERC for Mark and his team to test. The date SUERC came up was within 2000 years of the date established at Berkeley, but within uncertainty.

'Most of the lab work was carried out here in Berkeley, but SUERC made a huge contribution by verifying our results at very high precision, completely blind to our results,' says Renne.

The new results are the product of improved developments in isotope extraction and better data processing protocols at SUERC and BGC.

'There are probably 30 labs in the world that can do this type of dating work, but SUERC and BGC are two of only a few that can do it accurately at this level of precision,' says Mark.

The close proximity of both the extinction and the impact doesn't mean the impact was the sole cause. Dramatic changes in the climate over the millions of years preceding the impact, including long cold snaps after a general Cretaceous hothouse environment, probably brought many creatures to the brink of extinction. The impact may have just kicked them over the edge.

Team leader Paul Renne collecting a volcanic ash sample from a coal bed within a few centimeters of the dinosaur extinction horizon.

One possible cause of this change in climate was the sustained volcanic eruptions in India. Renne and Mark plan to re-date volcanic rocks from the Deccan Traps to get a better idea of when they appeared relative to the dinosaurs' extinction.

The researchers also found that Earth's atmospheric carbon cycle returned to normal around 5000 years after the asteroid impact. In contrast, the oceans took much longer to recover, only returning to normal one to two million years later.

'It looks like just 20,000 years after the impact mammals were already developing to fill the niche left by the dinosaurs. We were staggered it was so quick,' says Mark.