Haha I’m glad you won’t let me off so easily!
So apparently the “impact theory” is the most accepted answer (although of course there were no humans around at the time so we can’t know for sure). A massive meteorite is thought to have hit the Earth and the impact raised up a massive storm of dust and particles that ot stuck in the atmosphere. On top of that, the impact could also have caused all the volcanoes in the world to erupt so now we’ve got a massive dust cloud blocking out the sun, probably making it hard to breathe, and then lava coming at you from everywhere. Not a very nice way to go!