This question follows a previous Q&A, so you'll need to read previous chapters to get all of this.
Q: Wow, a lot to un-pack there (by no means a criticism.) In fact, thanks very much for the extensive informative responses!
My next question (maybe last, if I'm not pushing your patience too much here,) regards the truly catastrophic's. I'm 29 years old, which can't even be considered a mote in time when considering numbers like 13.7B or 4.5B, but nevertheless, here we are. Growing up it was accepted via the direction of our science teachers that dinosaurs were wiped out by an asteroid, and it seems to make sense. But alternative views like supervalcano's have been touted on science sounding TV channels as an alternative and I wonder about your thoughts on that. And minus dinosaurs, would we more statistically face worldwide threat from geology, a comet/asteroid, or a biological problem? We can leave out human stupidity towards ourselves for the sake of the argument. I guess cosmic factors too.
A: Most of humanity seems to gravitate towards a simple solution or answer to a complex problem. It's mentally easier. This is really obvious in the current political "debates" going on (Build a wall! Cut taxes! Increase spending on X!). The most difficult scientific problems to solve are the ones with more than one poorly-understood variable. MOST problems have complex causes. If my Microwave stops working, I think oh: it must be the power is out. Closer inspection shows that the power is there. Darn, no simple answer. OK, what's next to check then?
The Chicxulub event certainly had a big impact (pun intended) on saurian life when it hit 66M years ago, but there IS evidence that Life for Large Saurians was getting more and more difficult, with environmental degradation due to several things already underway, including volcanism (it was possibly accelerated by the formation of the Deccan Traps). However, make no mistake: a 2-cm layer of ash full of 1000-times-normal iridium in Gubbio, Italy, came from the Gulf of Mexico. A 10-km-diameter asteroid carries a ginormous amount of kinetic energy with it. The Earth's gravity well is pretty strong (a rock dropped from the Lagrangian point between Earth and Moon reaches about 19 km/second). This is also the speed of a minimum Earth orbit. The Chicxulub object certainly had a much higher velocity than that, and energy is mass times velocity squared. Double the velocity and you quadruple the energy delivered (it's a principle I teach to my Jujitsu students). From several studies there is a consensus that the Chicxulub kinetic energy before atmospheric entry was about 5.4 x 10^23 Joules, or 130,000,000 Megatons of TNT equivalent. By comparison, the largest hydrogen bomb ever detonated (by the Soviets, at Novaya Zemlya) was just 57 Megatons.