There’s a whole ecosystem underground. Animals, insects, fungi, bacteria. At some depth, the disruption above would have much less impact. Enough survivors to restart the surface world.
Saw this article today.
“This new hypothesis posits that most land-dwelling creatures were dead within hours of the asteroid’s impact.”
Yep, that’s just a popsci article referencing the JoGR paper I linked above.
Can we be sure it wasn’t actually mushroom-infested zombie dinosaurs that killed off the rest of the dinosaurs? This hypothesis is actually fleshed out pretty well as a thought experiment in a documentary on HBO. Perhaps you’ve heard of it? I believe it’s called The Last of Us.