Double large asteroid collisions 35 million years ago did not change Earth’s climate in the long term

Chicxulub is the asteroid impact that wiped out non-avian dinosaurs and many other living organisms on the planet 66 million years ago – but it wasn’t the last major impact. Two asteroids of almost the same size fell to Earth 35.65 million years ago, but their impact was very different. Despite the devastation, they do not appear to be causing long-term climate change.

The events took place 25,000 years apart. The diameter of an asteroid was between 5 and 8 kilometers (3-5 miles) and created the Popigai crater in Siberia, a depression 100 kilometers (60 miles) in diameter. Another asteroid, 3 to 5 kilometers (2-3 miles) wide, struck what is now the east coast of the United States, creating the Chesapeake Bay crater, between 40 and 85 kilometers (25-55 miles) in diameter.

These are the fourth and fifth largest craters on Earth. It is likely that larger craters were obliterated by our planet’s geological and atmospheric forces. Nevertheless, these were major events – but it turned out that their long-term effects appeared to be non-existent. Scientists looking for evidence of climate changes over the next 150,000 years found no lasting changes.

The team studied the chemical composition of tiny shell organisms that lived in the sea 35.5 to 35.9 million years ago. In particular, they studied isotopes, versions of the same atoms with different numbers of neutrons. The pattern of these isotopes gives scientists information about the temperature of the water. From this they can deduce changes in the climate.

“The remarkable thing about our results is that there was no real change after the impact. We expected the isotopes to shift one way or the other, indicating warmer or cooler water, but that didn’t happen. These large asteroid impacts occurred and in the long term our planet appeared to continue moving as usual,” said co-author Professor Bridget Wade of University College London in a statement.

“However, our study would not have captured short-term changes over tens or hundreds of years because sampling occurred every 11,000 years. On a human time scale, these asteroid impacts would be catastrophic. They would trigger a massive shockwave and tsunami, widespread fires would occur, and large amounts of dust would be thrown into the air and block sunlight.”

The samples were taken from the ancient seabed and the ancient sea surface and are largely consistent. Previous studies of the climate in the late Eocene were inconclusive. This geological period is marked not only by the Popigai and Chesapeake impacts, but also by three smaller impacts that may indicate something is happening in the asteroid belt.

“Given that the Chicxulub impact likely caused a major extinction event, we were curious to investigate whether what appeared to be a series of significant asteroid impacts during the Eocene also caused long-lasting climate changes. “We were surprised to find that there was no significant climate response to these impacts,” added co-author and MSc Earth Sciences graduate Natalie Cheng.

“It was fascinating to read about Earth’s climate history through the chemistry preserved in microfossils. It was particularly interesting to work with our selection of foraminiferal species and discover beautiful examples of microspheres.”

The article was published in the journal Communications Earth & Environment.