Chicxulub is the asteroid impact that wiped out the non-avian dinosaurs and many other living organisms across the planet 66 million years ago – but it was not the last major impact. Two asteroids that were almost as big fell to Earth 35.65 million years ago, but their effect was very different. Despite the devastation, it appears that they cause no long-term changes to the climate.
The events took place within 25,000 years of each other. One asteroid’s diameter was between 5 and 8 kilometers (3-5 miles) and created the Popigai crater in Siberia, a depression 100 kilometers (60 miles) across. Another asteroid 3 to 5 kilometers (2-3 miles) wide slammed into what is now the East coast of the US, creating the Chesapeake Bay crater which has a diameter between 40 and 85 kilometers (25-55 miles).
These are the fourth and fifth largest craters on Earth. It is likely that bigger craters have been erased by the geological and atmospheric forces of our planet. Still, these were major events – yet it turned out that their long-term impact appears to have been non-existent. Scientists who looked for evidence of changes in climate over the following 150,000 years found no lasting changes.
The team looked at the chemical composition of tiny shelled organisms that lived in the sea between 35.5 and 35.9 million years ago. In particular, they were looking at isotopes, versions of the same atoms with different numbers of neutrons. The pattern of these isotopes tells scientists about the temperature of the water. From that, they can work out changes in the climate.
“What is remarkable about our results is that there was no real change following the impacts. We expected the isotopes to shift in one direction or another, indicating warmer or cooler waters, but this did not happen. These large asteroid impacts occurred and, over the long term, our planet seemed to carry on as usual,” co-author Professor Bridget Wade, from University College London, said in a statement.
“However, our study would not have picked up shorter-term changes over tens or hundreds of years, as the samples were every 11,000 years. Over a human time scale, these asteroid impacts would be a disaster. They would create a massive shockwave and tsunami, there would be widespread fires, and large amounts of dust would be sent into the air, blocking out sunlight.”
The samples were taken from the ancient seafloor and the ancient sea surface, and they are in broad agreement. Previous investigations into the climate in the late Eocene period have been inconclusive. This geological period is not only marked by the Popigai and the Chesapeake impact, but three smaller impacts as well, maybe hinting at something happening in the Asteroid Belt.
“Given that the Chicxulub impact likely led to a major extinction event, we were curious to investigate whether what appeared as a series of sizeable asteroid impacts during the Eocene also caused long-lasting climate changes. We were surprised to discover that there were no significant climate responses to these impacts,” co-author and MSc Geosciences graduate Natalie Cheng added.
“It was fascinating to read Earth’s climate history from the chemistry preserved in microfossils. It was especially interesting to work with our selection of foraminifera species and discover beautiful specimens of microspherules along the way.”
The paper is published in the journal Communications Earth & Environment.
Source Link: Double Major Asteroid Collisions 35 Million Years Ago Didn’t Change Earth's Climate Long Term
