They were waiting.
Right before the rocks fell from the sky, something was already dying in North America.
Johns Hopkins University researchers dug into 66-million-year-old dirt from Colorado. They found microfossils of fungi. Lots of them. This confirms the asteroid didn’t just kill dinosaurs with impact. It triggered a global fungal bloom. But here is the twist. There was a second bloom. A quieter, deadlier one, tens of thousands of years before the fireball.
Fungi are life forms that thrive on calamities
The Before Times
We usually talk about the asteroid. The big boom. The end of the Cretaceous. But these guys—Rosanna Baker and Arturo Casadevall—found evidence of a prior crisis. About 30,000 years prior to impact. Fungal spikes. High density.
Why? Volcanoes in India.
Deccan Traps. Massive eruptions. Temperatures dropped. Ecosystems stressed out. Some species started fading early.
It makes sense if you look at it this way. The volcanism weakened the board. The asteroid was just the final strike.
Baker put it simply: “There is other evidence from the fossil record some species were dying off at this time.”
So the planet wasn’t healthy before the hit. It was already bleeding.
The Big Event
Then came the Chicxulub impact.
In the Denver Basin, the rock layers tell a violent story. The strata matching the asteroid show a massive jump in fungi compared to pollen or plant matter. Plant life crashed. Fungi took over.
This matches what scientists found in New Zealand years ago. But that was a single site. This? This is North America. It turns the local oddity into a global pattern.
The Cretaceous ended with a bang, yes. But it also ended with mold. Everywhere.
Aftermath and Mystery
Then things got weird.
Roughly 2,000 years into the Paleocene, the fungi surged again. Ten thousand years post-impact.
We don’t know why. No massive volcano. No asteroid. Just… growth.
The researchers also checked North Dakota. The Williston Basin. Same era. No fungal spike during the asteroid hit. Strange? Yes. But different rock types. Preservation issues happen. Still, the pre-impact and post-impact data held true there.
It wasn’t a localized Colorado fluke. It was a continent-wide pattern, mostly.
Warm Bodies Win
This changes the mammal narrative.
We like to think mammals survived because they were small, or clever, or burrowing. Maybe. But the science points to something physical. Heat.
Reptiles are cold-blooded. Their bodies stay cooler. Ideal for fungal spores. Mammals run hotter. Warmer temps mean a hostile environment for fungi.
Proliferation gave mammals a critical advantage over reptiles
Casadevall puts the nail in the coffin: mammals won the planet because their running furnace kept the rot away. While dinosaurs struggled with spores and dying plants, small mammals shook off the damp, the mold, and the death.
They evolved in a fungal apocalypse. And their blood was just hot enough to survive it.
The findings sit in PNAS. Solid peer review.
We used to think it was one event. One bad day. It was three.
What else did we miss?
