If WWII is any indication, if a war were to break out with a nuclear-armed state, it would end abruptly. The bombed state(s) would either surrender in the face of certain destruction after the first bomb or two fell, or their military capacity would be so devastated by the strikes that they would be unable to mount an effective campaign.
Couple the brevity of a nuclear war with the higher number of potential combatants and civilians that would be killed in a conventional shooting/firebombing war, and the proportionally higher power of conventional weapons than in WWII, and it's not at all clear that nuclear weapons would increase the overall destructiveness of a major war.
It is clear, however, that major powers are loath to start a potential WWIII because of nuclear weapons, thus saving tens or hundreds of millions of lives. That's what the Cold War was about.
Since it occurred 40 million years ago, it must have killed off the dinosaurs.
If it's taken the light from the supernova 40 million years to reach Earth, then wouldn't it take any deadly radiation at least that long to reach us? The dinosaurs missed out on any possible threat from this explosion by about 40 million years.
That's been illegal in the U.S. for cows for many years.
Not so. The FDA ban on feeding cattle protein to cattle excepts proteins derived from blood products and fat, and beef tallow is still used as a feed supplement at cattle farms. Also, since the bovine meat and bonemeal that used to be fed to cattle are still fed to other food stock like pigs and chickens - whose meal is, in turn, an accepted protein supplement for cattle - there is still a chance that infectious prions could find their way back into cattle (and us). Check out Michael Pollan's book, The Omnivore's Dilemma, for more info.