The end-Cretaceous mass extinction event 66 million years ago is well known to have caused the death of the non-avian dinosaurs, along with at least 50 percent of all plant and animal life on Earth. Most scientists point to a massive asteroid impact as the primary antagonist, but it is true that huge floods of lava released from the Deccan Traps also contributed to the demise of the dinosaurs. A new study published today in Nature Geoscience has for the first time provided a quantifiable estimate on just how much the epic curtains of volcanic fire had an effect – surprisingly, it was far weaker than previously thought.
Flood basalts are vast eruptions of both lava and atmosphere-altering gases and aerosols that spread out on a continental scale. They have an enormous effect on the world’s climate, with massive amounts of sulfur dioxide causing it to cool rapidly by reflecting much of the incoming solar radiation back into space.
After a massive asteroid impact, large quantities of debris are launched into the atmosphere, which also block out the sunlight. The combination of both throws the world into a volcanic winter, wherein photosynthesis struggles and plant life dies off – triggering a chain reaction of die-offs further up the food chain. Some studies actually suggest that the compression of the Earth’s crust after an asteroid impact would lead to increased volcanism as magma is forced up to the surface.
This new study by researchers at the University of Leeds used computer simulations to model the effect of the continental flood basalt eruptions, taking into account the spread of the released gases and aerosols through the atmosphere. They found that the Earth's atmospheric temperature would have indeed cooled by 4.5°C (8°F) in only a million years – a hugely destabilizing global temperature change. However, the temperature would have returned to normal within just 50 years – far faster than they thought.
“Perhaps most intriguingly, we found that the effects of acid rain on vegetation were rather selective. Vegetation in some but not all parts of the world would have died off, whereas in other areas the effects would have been negligible,” Dr Anja Schmidt, lead author of the study, said in a statement.
Image credit: The rapid return to "normal" temperatures surprised the scientists. Wead/Shutterstock
Trying to explain what causes a mass extinction event is incredibly difficult. The causes behind two, the end-Permian (also known as the Great Dying) and the end-Cretaceous, are considered to be fairly well known, even if the degree to which each perpetrator contributed to the events is debated. Others, however, have highly debatable causes, ranging from the sudden emergence of a new animal group to an exploding nearby star.
It seems likely in these cases, and indeed in the complex end-Cretaceous extinction event, that there were multiple causes, not just one. Paleontologists have a quirky term for this: the “Murder on the Orient Express” Model, named after the eponymous Poirot murder-mystery tale by Agatha Christie in which everyone on the train is responsible for the homicide.
In this case, although the importance of each are debated, both volcanism and the major asteroid impact likely contributed to the death of the wandering giant lizards, among others – even if the effect of the volcanism was less severe than previously thought.