This is the natural disaster to worry about

What happens if I heat up this rubber band? When you heat materials like glass or plastic, the atoms vibrate faster. They get slightly farther apart and this reduces intermolecular forces. So, the material gets weaker.

Under tension, it stretches. But when I heat up this rubber band, the opposite happens. It actually pulls more strongly. The rubber band contracts and the weight goes up.

So, why does this happen? Well, rubber is unlike any other material. It's waterproof. As it's breaking, it actually becomes tougher, and it can stretch up to 10 times its length and bounce back, no worse for wear.

These properties have made it essential for modern life. It forms the tubes and seals that carry our gas and water, the belts that drive our motors, and the tires on our cars, trucks, and planes. Even trains use rubber in their suspension systems. It's a perfectly engineered material, but we didn't invent it.

All of our most durable rubber still comes from a single natural source. This tree, it's a source at risk of being wiped out. And if that happens, the results could be devastating. >> You're talking about a complete global societal meltdown.

>> This could be considered a national security issue. You wouldn't think that we're so dependent on this thing. >> Well, we are. And most people don't know that.

They're waiting for a disaster to happen. >> Rubber comes from the Brazilian rubber tree. As early as 1600 BC, Mesoamericans cut the bark to release this milky white liquid, now known as latex. They noticed that if they let it dry, it turned into this stretchy waterproof solid lump.

To see this in person, we sent Veritassin producer and mechanical engineer Henry van Djk to the Akran Research and Development Laboratory where they specialize in all things rubber. In just all these racks, even though they look solid, they're all flowing right now. Really? >> If you look behind one of these racks, you can see these are actually dripping.

>> Oh, wow. >> They're flowing slower than we can perceive. >> Unprocessed rubber is not the rubber we're used to. it slowly flows and can't maintain its shape.

So, how do you get this weird material in the first place? Well, just underneath the bark are special tube-like cells that carry the latex. Floating around inside are lots of isopentinyl ...