Do all asteroid impacts change the world forever?
When we think of asteroid impacts, our minds often drift to catastrophic events like the one that wiped out the dinosaurs 66 million years ago. However, not all collisions with space rocks leave such a lasting mark on Earth’s climate or ecosystems. Take the late Eocene period, for example, when two massive asteroid impacts struck Earth—yet life and climate seemed to carry on almost undisturbed in the long term.
A Tale of Two Craters
Roughly 35.65 million years ago, two significant asteroid impacts occurred just 25,000 years apart, a blink of an eye in geological terms. The first asteroid, measuring between 5 and 8 kilometers across, struck what is now Siberia, leaving behind the 100-kilometer-wide Popigai crater. The second asteroid, slightly smaller at 3 to 5 kilometers in diameter, created the Chesapeake Bay crater on the modern-day East Coast of the United States, with a diameter of 40 to 85 kilometers.
These craters rank as the fourth and fifth largest known on Earth. Larger craters may have once existed but were erased by geological and atmospheric processes over millions of years. Despite the enormous energy released during these impacts, researchers have found no evidence of long-term climate disruption following these events.
What Microfossils Reveal
To unravel the mystery, scientists turned to the chemical signatures preserved in tiny marine organisms called foraminifera, which lived in the oceans between 35.5 and 35.9 million years ago. By analyzing isotopes—variants of elements with different neutron counts—within these microfossils, researchers reconstructed sea temperatures from the time. Astonishingly, the data revealed a steady climate with no significant temperature shifts in the aftermath of the impacts.
Professor Bridget Wade from University College London explained the findings: “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.”
Still, this does not discount short-term effects. Dust and debris from such collisions likely caused shockwaves, tsunamis, and temporary atmospheric changes, such as blocking sunlight. However, because the microfossil samples span 11,000-year intervals, these brief disruptions were undetectable in the study.
Implications of Eocene Impacts
The late Eocene period wasn’t just marked by these two giant impacts. Researchers note at least three smaller asteroid collisions around the same time, raising questions about a possible spike in asteroid activity—perhaps a disturbance within the Asteroid Belt. Despite this bombardment, life on Earth appeared remarkably resilient, avoiding the mass extinctions seen after the Chicxulub impact.
Graduate researcher Natalie Cheng shared her perspective: “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.”
These findings shed new light on Earth’s capacity to recover from extraterrestrial collisions. While the Chicxulub event remains a stark reminder of nature’s fragility, the late Eocene impacts suggest that not every asteroid leaves an indelible mark on our planet’s history.
