When we read about the downfall of the Roman empire, the Mongols, or even the dinosaurs, we can't help but wonder if our own modern civilization might be susceptible to something similar. 

There have been five mass extinction events in our planet's history, (defined as when at least half of all species die out in a relatively short time), the first of which occurred around 450 million years ago. The most recent mass extinction is the one you probably know the most about, and happened 65 million years ago when an asteroid struck Earth, wiping out the dinosaurs among many other creatures. By that math, you might notice that we're due for a 6th pretty soon, and you'd be right. Many scientists believe that we're actually experiencing the start of that 6th mass extinction, thanks to global warming. 

But everyone knows about global warming and asteroids. What are some threats that could wipe us out, but we aren't paying attention to? That's what the people in this gallery aimed to answer, and I for one won't be sleeping as well tonight after constructing it. Here are 25 apocalyptic scenarios you might not be aware of.