We all know about the asteroid that wiped out the dinosaurs 66 million years ago. But there have been other impacts in (slightly) more recent times, with subtler effects.

The Earth was struck by 2 huge asteroids 35 million years ago – but it managed to shrug off the impacts, according to a new study.

The study, published in Communications Earth & Environment finds that – other than 2 massive craters – there’s little evidence of long-term effects caused by the asteroids.

But the researchers point out that in the short-term – over decades, or centuries – the collisions would have changed life on Earth dramatically.

The researchers examined isotopes (signatures in atoms) from fossils preserved in the Gulf of Mexico seafloor for signs of climatic change.

“What is remarkable about our results is that there was no real change following the impacts,” says study co-author Professor Bridget Wade, a researcher in earth sciences at University College London, UK.

“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.”

The 2 asteroids struck the Earth 25,000 years apart, 35.65 million years ago.

One of the asteroids is estimated to have been 5-8km wide, causing the 100km Popigai crater in Siberia, Russia.

The second is estimated at 3-5km wide, causing the 40-85km crater in Chesapeake Bay, USA. The craters are the 4th and 5th largest known craters in the world.

“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,” says co-author Natalie Cheng, a geosciences graduate at University College London.

The researchers looked at more than 1,500 fossils between 35.5-35.9 million years old, hunting for any evidence in the carbon and oxygen atoms that the Earth’s climate changed after the asteroids hit.

They found tiny silica droplets which were likely caused by the asteroid impacts, but they did not find any evidence of climatic change.

“We were surprised to discover that there were no significant climate responses to these impacts,” says Cheng.

This does not mean the asteroid impacts went unnoticed.

“Our study would not have picked up shorter-term changes over tens or hundreds of years, as the samples were every 11,000 years,” says Wade.

“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.

“Modelling studies of the larger Chicxulub impact, whichkilled off the dinosaurs,also suggest a shift in climate on a much smaller time scale of less than 25 years.

“So we still need to know what is coming and fund missions to prevent future collisions.”