Because of volcanic eruptions

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Dinosaurs lived in climatically turbulent times - but after the asteroid impact, their era was over.

(Bild: Melisande - stock.adobe.com)

Even before the devastating asteroid named "Chicxulub" after its impact site off the coast of Mexico, dinosaurs and co. lived in climatically turbulent times. This is the result of a new analysis by a research team with Austrian participation in the journal "Science Advances". 

According to the study, it became a total of around three degrees Celsius warmer in the decades leading up to the dinosaurs, but also cooled down quite abruptly by up to five degrees in between. The reason: enormous volcanic eruptions.

In the period before the Chicxulub impact around 66 million years ago, the Earth was in a state of emergency, as analyses repeatedly suggest. The enormous volcanic activity that led to the current appearance of the Deccan highlands on the Indian peninsula is likely to have been responsible for this. The "Deccan Trapp" is formed by staircase-like deposits that still tower hundreds of meters high today. They consist of volcanic rock, which repeatedly poured over an area of around 500,000 square kilometers even before the asteroid impact.

Mass extinction wiped out 75 percent of the species
It is clear that such volcanic eruptions also released large quantities of greenhouse gases such as CO2 or sulphur compounds into the atmosphere over thousands of years - with corresponding effects on the global climate at the time. In the past, some scientists even considered the eruptions to be potent enough to be the main cause of the huge extinction event at the transition of the Cretaceous-Paleogene boundary.

After all, an estimated 75 percent of all species died out at that time, as the team writes in its publication. In fact, there were relatively abrupt, massive changes at that time, which the majority of researchers now associate with the impact of the asteroid that wiped out the dinosaur era.

Eruptions bring long-term warming
With regard to possible contributions of the Deccan super-volcanoes, it is clear on the one hand that large amounts of CO2 drove the greenhouse effect that can also be observed today and thus brought about an increase in temperature. On the other hand, there were also short-term climate effects to the contrary, when large quantities of sulphur dioxide were converted into sulphate aerosols around the largest eruptions in the atmosphere, which in turn had a cooling effect.

Temperature estimate thanks to ancient bacterial remains
The team led by Lauren O'Connor and Bart van Dongen from the University of Manchester (UK), which also included Sabine Lengger, who currently works at Silicon Austria Labs (SAL), analyzed ancient remains of cell membrane lipids of soil bacteria in lignite preserved at two sites in the USA that lived during the period in question. These structures are slightly different in the bacteria when they grow up in different temperatures, according to the researchers, who calculated an average temperature per millennium before the geological Cretaceous-Paleogene boundary that is clearly visible in the samples on the basis of these investigations.

Overall, the team believes that the results from the two sites, which are around 750 kilometers apart, fit together well. In the period from 100,000 years before the impact to the impact itself, the temperature rose by around three degrees Celsius. It is clear that one of the four major eruption pulses - the "Poladpur pulse" - falls within the period under investigation. These were characterized by huge eruptions that sometimes lasted for centuries, the scientists write.

Marked drop in temperature
They also attribute the temperature drop of two to five degrees Celsius, which lasted for around ten thousand years and is found 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 around 50 years after the end of the largest eruptions, peaked around 30,000 years before the devastating impact. However, temperatures rose again immediately afterwards. For the researchers, the study shows that although the climatic upheavals before the Chicxulub asteroid undoubtedly caused great stress to the flora and fauna at the time, they were not the main factor behind the mass extinction.