I’ve been catching up on a lot of the science that’s happened in 30 years since I had a formal science class, especially genetic studies and fossils that support evolution in really remarkable ways. Some of the more fascinating examples come from evolutionary paths since the Cretaceous-Paleogene extinction event.
Keep in mind that even though the Alvarez hypothesis was present in the “Dinosaurs for early readers” books I loved in the '80s, it was always present as a hypothesis among others. Even in this thread from 1999 that Discourse recommended to me, it’s treated with some skepticism. Now, of course, with more evidence collected about the Chicxulub impact it’s widely accepted.
Likewise, the theories that whales evolved from land mammals and birds evolved from dinosaurs were considered possibilities and are now supported by a mountain of genealogical and fossil evidence.
What still seems up for debate, though, is how quickly it happened. Where the Permian-Triassic extinction event taking 100,000+ years of volcano-induced climate change, scientists are starting to support theories that the Cretaceous extinction happened in 10,000 years or less, with some proposing that it was much, much less.
I find their arguments compelling. What I’m learning now is that avian dinosaurs that we would recognize as “birds” today (lay eggs, have feathers, are sometimes capable of flight, have beaks) evolved long before the extinction event. Likewise, mammals hard started to diversify. And yet, the only species that survived the event were – small, burrowing, omnivorous, scavengers. Chickens and rats, basically. Swamp critters in a similar ecological niche also survived, and in the oceans, everything in the water column died except for bottom feeders that would eat decaying animals. As for plants, with few exceptions only plants with hardy seeds survived – the type that survive forest fires today, for instance.
To me, this paints a picture of an almost immediate famine. Material would have been ejected from the asteroid impact, blocking out the sun and acidifying the oceans, but then almost immediately would have started settling back to the ground. The first year would be brutal – all plant life dying in the first few weeks, primary consumers starving after that, secondary consumers and on. Months, perhaps, before everything was dead except the species that could survive on detritus, dead animals, and seeds.
But if that went on too long, nothing would have survived, so it seems plausible that the next year saw seeds sprouting, the skies clearing, and oxygen supplies in the ocean recovering. That process may have taken hundreds or thousands of years to return to normal, but the hardy species that survived the first few months would have been able to survive through that period.
The alternative theory, I suppose, is that the impact made the conditions bad but not completely inhospitable, and plesiosaurs and triceratops continued to live for hundreds or thousands of years while competing with each other for dwindling resources until more conventional extinctions happened one by one. I’m not smart enough on this to know if this makes sense but my uninformed gut can’t come to terms with this.
Anyway, I’m sure I sound like a goober talking about things I know little about, but is there any reason to doubt the idea that the extinction event was really mostly done in 1-2 years? As crazy as that might seem in geological terms?