There are approximately 15 000 nuclear weapons on the planet. The largest one as far as I am aware is the Tsar Bomba, which packs a punch of (rounding here) 100 megatons of TNT. So if all of them were Tsar Bombas, we'd be looking at 15 000*100 megatons TNT = 1 500 000 000 000 tons TNT. Source: https://en.wikipedia.org/wiki/Tsar_Bomba Meanwhile, the comet that killed the dinosaurs is estimated to have had a 100 trillion ton TNT equivalence. Source: http://scienceline.ucsb.edu/getkey.php?key=2200 So if 100 trillion tons TNT equivalence didn't destroy the planet, how is one trillion, five hundred billion? It's two orders of magnitude less, yet it's supposed to destroy the planet three times over? How? I'm not saying it might not destroy all of human society. I mean, one per major human city could certainly do that. And I'm not saying there wouldn't be massive repercussions down the line (nuclear winter, etc). But surely the Big One that destroyed the dinosaurs and countless other creatures had similar long lasting effects? So how are nuclear weapons capable of destroying the planet when the Dino-killing Big One, which was two orders of magnitude more powerful, was not?