Last updated June 7, 2018 at 2:37 pm
Impact affected Earth’s climate for far longer than expected.
An artist’s impression of the Chicxulub asteroid impacting the Yucatan Peninsula as pterodactyls fly in the sky above. Painting by Donald E. Davis. Credit: NASA
It was the most calamitous event in the history of Earth. A gigantic asteroid careening through space smashed directly into modern day Mexico, wiping out 75% of all life on Earth and ushering in the end of the dinosaurs.
Around 66 million years later we are still discovering how this apocalyptic event changed the face of the planet in an instant, from the effect on life to geology.
New research has found that it also affected the global climate far longer than might be expected – cranking up the planet’s temperature by 5 °C for 100,000 years after the impact.
And that recovery period, according to the researchers, may be relevant when we consider our impact on the atmosphere today.
Reconstructing the ancient climate
The after-effects of the Chicxulub impact are still debated, with some scientists arguing that that soot within the atmosphere blocked out the sun, leading to a global cooling. On the other hand, others suggest that carbon thrown into the atmosphere from the Earth’s crust upon impact as well as from wildfires, had an overall warming effect.
To unravel the consequences of the asteroid’s impact, the team of researchers from the University of Missouri looked towards Tunisia, an area renowned for its record of the Cretaceous-Palaeogene boundary. This thin layer of sediment holds the secrets of what happened when the asteroid crashed into Chicxulub in Mexico, triggering the mass extinction event.
By analysing the chemical composition and isotopes of oxygen contained in sand grain-sized remains of fish teeth, scales and bone, the researchers could reconstruct the temperature when the animal was alive. Their samples covered 50,000 years before the asteroid impact to over 300,000 years after, allowing them to build a timeline of Earth’s temperature before, during and after the asteroid’s impact.
What they found was a rapid rise in temperature by 5 degrees Celsius. That increase continued for 100,000 years before returning to pre-asteroid levels.
However, as climate swings tend to be larger at the poles than the equator due to an effect called polar amplification, it’s likely that the polar regions warmed even more than Tunisia, say the researchers.
The amount and duration of the warming closely matches levels of carbon dioxide that some types of analyses have estimated were emitted during the same period.
The Chicxulub crater has been filled in by sediments over the millions of years since impact. Using a gravity map, the crater’s topological features can be visualized. The red and yellow are gravity highs, and green and blue are gravity lows. The white dots indicate a network of sinkholes called “cenotes,”which were formed as a result of the impact. Credit: NASA
What about global cooling?
The Tunisian results are significant as it paints a picture from thousands of kilometres away from the impact site, suggesting that the sharp, prolonged warming was a global effect.
In the immediate area of the impact site there would likely still have been a temporary cooling, thanks to debris being thrown into the atmosphere from the impact blocking the sun.
However, according to Andrew Glikson from the Australian National University, who was not involved in the research, that local cooling would have soon been overridden by the global warming effect.
“The impact could cause a rise of dust, fragments, aerosols, sulfur dioxide and so on. This is the normal process,” he told the ABC.
“But carbon dioxide would be distributed and disseminated more uniformly, and much longer term, than dust and aerosols.”
While the sun-blocking particles may have stayed in the atmosphere for tens of years, the new research shows that the carbon dioxide-induced warming can stay for millennia.
Warming effects for millennia
It’s that long-term warming caused by the staying power of carbon dioxide which has the researchers drawing parallels with our current activities.
“The rate at which the planet system was perturbed by the impact is quite comparable to human perturbations over the past 200 years,” Ken MacLeod, who lead the research at the University of Missouri told the ABC.
“If we turn off our fossil fuel lifestyle tomorrow, it’ll still take 100,000 years for the changes we’ve already imposed upon the Earth to come back down to something like the pre-industrial revolution state.”
The research has been published in Science
