I have this one little saying. When things get too heavy just call me helium, the lightest known gas to man. -Jimi Hendrix

Hendrix is almost right: helium is the second lightest gas known to man, behind hydrogen. But there are many applications for helium -- both scientific and non-scientific -- that make it incredibly useful and practical. Helium is far lighter than air and is inert, which means it won't combust when you combine it with air and energy, like Hydrogen does (below).

(Too bad for the kids who want hydrogen balloons for their birthday parties!)

In addition to being lighter than air, Helium is incredibly useful, scientifically, in its liquid form! With a boiling point of only 4 Kelvin, liquid helium is used to cool some of the most powerful electromagnets on Earth, including those at Fermilab and the Large Hadron Collider. It's the first known superfluid, a fluid that has many interesting properties, including absolutely no viscosity, and it will never come to rest or lose energy once you start it in motion!

But -- as Lee Billings wrote earlier this week -- Helium is pretty rare on Earth, and. Although Helium is the second most common element in the Universe (behind Hydrogen), it's incredibly rare on Earth. There are only two places to find Helium. The first is the Earth's atmosphere.

The exosphere -- the uppermost layer of the atmosphere -- contains small amounts of Helium. Compared to the rest of the atmosphere, five parts per million are Helium, which means that extracting Helium from the atmosphere is incredibly inefficient and expensive, so much so that we don't do it.

Where do we get our Helium from, then? Believe it or not, we mine it from underground!

This above image is the U.S. Bureau of Land Management's Crude Helium Enrichment Facility in Texas. It supplies about 40% of the Helium produced in my country, and it all comes from pockets of Helium that live underground.

Want to know how it got there?

That's right; radioactivity! You see, when our Earth was formed, it was loaded up with a whole slew of unstable elements, including everything on the periodic table that's heavier than Lead, such as Uranium, Thorium, Radium, and Radon. Since these elements are unstable, they radioactively decay.

Even though some of these elements take billions of years to decay (on average), the Earth has been around for billions of years! Not only that, but there are three ways that particles can decay. The first type discovered -- alpha decay -- is when a radioactive particle emits a Helium nucleus!

Find a couple of electrons, and what have you got?

Helium! So if you get an ore of the right type of radioactive element, and you wait millions and millions (or even billions) of years, you make a giant underground store of helium!

So the good news is that these underground stores exist, so we have a supply of Helium for all of our scientific (and non-scientific) purposes. But the bad news? When we use it up, we'll have to wait million of years for it to build back up, or figure out some non-prohibitively expensive way to recover it from the atmosphere. (It's so expensive that many are thinking of mining the Moon when we're out of it on Earth!)

I'm all for environmentalism and conservation, but even if you aren't, running out of Helium poses a serious problem for the continuing advancement of science and technology. Helium on Earth is scarce. It took millions of years to make the stores we have now, and once they're gone, they'll be gone for thousands of generations.

So be careful with the precious things you have, and treat them like the precious things they are, even if others don't. Because some of them -- like Helium -- are truly irreplaceable.