Dinos experienced warm and cool weather in front of the asteroid

Over the past ten years, it has become a total of about three degrees Celsius warmer, but in between it has also become quite abruptly cooler to five degrees. The reason: huge volcanic eruptions.

In the period before the Chicxulub impact, about 66 million years ago, the Earth was in a state of emergency, as analyzes repeatedly suggest. The massive volcanic activity that led to the current creation of the Deccan highlands on the Indian peninsula was probably responsible for this. The “Dekcan Trap” is formed by step-shaped deposits that still accumulate hundreds of meters high today. They consist of volcanic rock, which continued to erupt over an area of ​​about 500,000 square kilometers even before the asteroid impact.

Mass extinctions have wiped out 75 percent of the species
It is clear that such volcanic eruptions over thousands of years also released large amounts of greenhouse gases, such as CO2 and sulfur compounds, into the atmosphere – with corresponding consequences for the global climate of the time. In the past, some scientists even believed that the eruptions were powerful enough to be seen as the main cause of the massive extinction event at the transition between the Cretaceous and Paleogene boundaries.

It was estimated that 75 percent of all species became extinct at the time, the team wrote in their publication. In fact, there were relatively abrupt, massive changes at the time, which the majority of researchers now associate with the asteroid impact that wiped out the age of the dinosaurs.

Eruptions cause long-term warming
Regarding the possible contributions of the Deccan supervolcanoes, on the one hand it is clear that large amounts of CO2 caused the greenhouse effect that can also be observed today and thus caused an increase in temperature. On the other hand, there were also short-term opposite climate effects, with large amounts of sulfur dioxide in the atmosphere being converted into sulfate aerosols around the largest eruptions, which in turn had a cooling effect.

Temperature estimation thanks to old bacterial remains
The team led by Lauren O’Connor and Bart van Dongen from the University of Manchester (Great Britain), which also included Sabine Lengger, currently at Silicon Austria Labs (SAL), analyzed ancient cell debris preserved at two locations in the US. -Membrane lipids of soil bacteria in lignite that lived during this period. These structures are slightly different in the bacteria when they grow at different temperatures, according to the researchers, who based on these studies calculated an average temperature per millennium before the Cretaceous-Paleogene boundary, which is clearly visible geologically in the samples.

Overall, the team believes that the results from the two sites, which are about 750 kilometers apart, fit together well. In the period from 100,000 years before the impact to the impact, the temperature increased by about three degrees Celsius. Clearly, one of the four major outbreak pulses – the ‘Poladpur pulse’ – falls within the study period. These were characterized by enormous eruptions that sometimes lasted for centuries, the scientists write.

Significant temperature drop
They also attribute the temperature drop of two to five degrees Celsius, which lasted about ten thousand years and is reflected in the data, to the Poladpur pulse. This cooling, caused by the aerosols, which largely disappeared from the atmosphere in the form of acid rain about fifty years after the end of the largest eruptions, reached its peak about 30,000 years before the devastating impact. After that, however, temperatures immediately rose again. For the researchers, the study shows that the climatic upheavals before the asteroid Chicxulub undoubtedly put severe pressure on flora and fauna at the time, but were not the main factor in the mass extinction.