New research may draw a 'curtain of fire' on dinosaur extinction theory
Release Date 23 November 2015
The role volcanic activity played in mass extinction events in the Earth's early history is likely to have been much less severe than previously thought, according to a new study.
Asteroid impacts and long-lasting volcanic eruptions called continental flood basalts - the two most commonly cited possible causes of mass extinction events - would have propelled gas and dust into the atmosphere and altered climate for years. But, until now, the impact of years of sulphur dioxide emissions from continental flood basalts was unknown.
In a study published online today in Nature Geoscience, researchers have provided for the first time a quantitative estimate of the degree and nature of the effects that such eruptions had on the Earth's climate, vegetation and oceans.
The work was carried out by a team led by the University of Leeds, which included the University of Reading's Professor Richard Skeffington from the School of Archaeology, Geography and Environmental Sciences.
Study lead author Dr Anja Schmidt, from the University of Leeds, said: "At the time when the dinosaurs reigned, numerous long-lasting eruptions took place over the course of about a million years. These eruptions, called ‘continental flood basalts' were not like volcanic eruptions we often see today, with lava gushing from the ground like a curtain of fire.
"Each eruption is likely to have lasted years, even decades, and eruptions were separated by periods without volcanic activity. The lava produced by an eruption of average intensity would have filled 150 Olympic-size swimming pools per minute."
'Given the sporadic nature of the eruptions, damage due to acidification of soils and waters would have been geographically-limited and not sufficient to cause global extinctions' -- Prof Richard Skeffington, University of Reading
In the new study, the researchers used a sophisticated computer simulation of the spread of the gas and aerosol particles, which showed that the climatic impacts of flood basalts was less grim than scientists had previously suggested. They found that only if such flood basalts oozed for hundreds of years, without interruption, may the climatic impacts have had a severe effect on plants and animals.
The researchers used information on the duration and intensity of continental flood basalt eruptions, such as the Deccan Traps eruptions 65 million years ago, which covered one-third of what is now India, to estimate the climatic and environmental effects of the huge quantities of sulphur dioxide gas emitted by these eruptions.
Their computer simulation showed that temperatures on Earth were indeed cooler as a result of the eruptions - by as much as 4.5 degrees Celsius - but that the temperature would return to normal within 50 years after an eruption ceased.
Dr Schmidt noted that the conclusions are based on the assumption that climate feedbacks were very similar to those today.
The study also included an assessment of the effects of sulphur dioxide and the resulting acid rain on the ecosystems present at the time, performed by University of Reading researcher Professor Richard Skeffington.
"Working out the environmental effects of events so far in the past was very challenging", said Professor Skeffington.
"We used the extensive knowledge we now have of the effects of acid rain on modern species and environments, and computer models which have been developed to calculate those effects. This knowledge is the basis for modern air pollution control legislation, and it was an interesting exercise to apply it to events of millions of years ago.
"What we found was that given the sporadic nature of the eruptions, damage due to acidification of soils and waters would have been geographically-limited and not sufficient to cause global extinctions. Direct damage by acid mists and fogs appeared to be the most potent mechanism, but this would have only affected high-altitude areas."
The new findings will challenge the earth sciences community as a whole to re-examine the causes of mass extinctions and the role of volcanism. "We now need to better understand how long both the individual eruptions and the periods without volcanic activity lasted," concludes Dr Schmidt.
The research paper, ‘Selective environmental stress from sulfur emitted by continental flood basalt eruptions', is published online by Nature Geoscience on 23 November 2015.
Photo shows Lava fountaining above the volcanic fissure of the Holuhraun flood basalt eruption in Iceland in September 2014, which can be considered as a smaller scale analogue for the eruptions in the Deccan Traps, 65 million years ago. Credit: Michelle Parks (University of Iceland)