Most people don't really give how precarious human civilization really is. That's mainly because they have better things to do than to worry about that kind of thing. I, on the other hand, don't really have anything better to do sometimes than to think and read about this kind of thing.

For example, while many people know that an asteroid nailed the earth 65 million years ago, wiping out the dinosaurs along with most other large animals in the ocean and on land, most people aren't aware of how common smaller but civilization ending hits are.

First some perspective: Life is thought to have really gotten going around 400 million years ago or so.  Sure, there was life before the "pre-Cambrian explosion" but nothing very complex. 400 million years.

The last 65 million years saw mammals slowly rise and fill the niches left by the Dinosaurs.  Somewhere around 6 million years ago humans and chimps parted ways (though technically speaking, we're still so similar to chimps from a DNA point of view that we are really just another species of chimp but I digress).

Depending on who you talk to, only around 200,000 to 50,000 years ago to modern humans arise. The debate has to do with whether anatomically modern humans or intellectually modern humans are the same thing (why did cave painting start only 50,000 years ago?)

Regardless, from 50,000 years ago to around 5,000 years ago humans were basically running around in small tribes following herds of grazing animals across Africa and Asia other than a bunch of adventurous tribes that decided to go into North America around 10,000 to 15,000 years ago (not to mention the crazies who went down into Australia).

But real human civilization -- as in towns and cities, really only got going around 3000 years ago and that's being generous.  Rome only got going 2100 years ago.

And what I'll call hyper-specialization only got started 100 years ago or so. What's the point of this and what's hyper-specialization?

Well, hyper-specialization is basically specialization to the point where the majority of people are basically incapable of living without our modern system of logistics. If civilization came to an end, I'd be food for something pretty quickly.  Without contacts I'm pretty much blind. I can't farm. Can't hunt. Don't have any useful survival skills. In other words, I'm a typical surbanite.

And here's the bad news: Pretty bad things happen to Earth pretty regularly. Smaller asteroids strike the earth every 10,000 to 20,000 years. These hits don't wipe out the earth of course but it's certainly enough to shut down food production worldwide pretty seriously. There's 6 billion people these days on Earth. That number is only sustainable thanks to modern agricultural techniques. But take away say, sunlight, for a couple of years due to a small asteroid hit and most of us would be dead.

And there are plenty of other nasty things that happen on occasion. Super volcanoes, mega earth quakes, etc. that would be enough to completely disrupt the world economy in ways that would lead to billions of deaths. And it's not stuff that happens every 50 million years, it's stuff that our ancestors lived through already countless times but didn't know how to record these events. And it will happen again. The difference is that unlike say 20,000 years ago we have large segments of modern world that would not deal very well to the modern logistics miracles that came with the 20th century.