The catastrophic demise of non-avian dinosaurs is famous as the most devastating event for life on our planet. However, there have been hints that the asteroid impact might not have been the main cause of this mass extinction, but rather just the most spectacular isolated event.
Prior to this dramatic event 66 million years ago, there were indications that toxic atmospheric changes were already underway.
An international research team has conducted a new analysis providing evidence that the world before the asteroid impact was not the paradise it may seem, with sulfur in the atmosphere reaching critical levels.
Together with other studies on mercury levels, the research presents a pattern of volcanic activity that could have caused significant disruptions to the Earth’s climate.
In 1991, the timing of this volcanic activity was disregarded as too early to be linked to the mass extinction event, but more recent studies suggest it may have been close enough to be significant.
“Our data suggest that volcanic sulfur degassing could have caused repeated short-lived global drops in temperature,” write University of Oslo geoscientist Sara Callegaro and colleagues in their paper.
The team examined rocks from the Deccan Traps – one of the largest volcanic features – in what is now West India, using a new technique to measure sulfur concentrations.
Models suggest that sustained sulfur emissions from the Deccan Traps were enough to significantly alter the global climate. This volcanic region alone released a staggering one million cubic kilometers of molten rock.
Furthermore, the formation of highly concentrated sulfur-containing lava within the region coincides with the cooling Cretaceous climate, the team notes.
While much of the basalt in the area is generally low in sulfur, this could indicate that the cooling molecule was slowly released into the atmosphere from the hardened magma following eruptions.
Consequently, global temperatures could have plunged by up to 10°C, with rapid recovery periods, within 100,000 years before the Chicxulub meteor delivered its final blow.
“Our research demonstrates that climatic conditions were almost certainly unstable, with repeated volcanic winters that could have lasted decades, prior to the extinction of the dinosaurs,” explains McGill University geochemist Don Baker.
“This instability would have made life difficult for all plants and animals and set the stage for the dinosaur extinction event.”
Fossilized bone fragments and thousands of eggshell remnants have suggested a global decline in non-avian dinosaur species over a prolonged period.
But these declines have been contradicted by other studies, continuing a long-standing and sometimes bitter scientific debate between the asteroid and volcano theories. Some researchers suggest the asteroid may have triggered greater activity from the Deccan Traps, while others claim the volcanic activity may have helped life recover from the asteroid strike.
The argument for pulses of eruptions seems to be gaining support, and after all, volcanoes brought about a global biotic crisis during the previous mass extinction event.
“Deccan Traps volcanism set the stage for a global biotic crisis, repeatedly deteriorating environmental conditions by forcing recurring short volcanic winters,” the team concludes.
Their findings were published in Science Advances.