Helium

We usually think of helium as that stuff that goes in balloons, but it is much more. It is formed by the slow and steady radioactive decay of terrestrial rock and is the second most abundant element in the Universe, but very rare on Earth. Helium is used for keeping  satellite instruments cool and to clean out rocket engines. It was also used to cool the liquid oxygen and hydrogen that powered the Apollo space vehicles.

Helium is used as a cooling medium for the Large Hadron Collider  and the superconducting magnets in medical MRI scanners. It is often used to fill party balloons, weather balloons, and airships because of its low density. Helium-neon gas lasers are used to scan barcodes at supermarket checkouts.

A mixture of 80% helium and 20% oxygen is used by deep-sea divers and others working under pressurized conditions.

It also makes for fun differences with our vocal cords. When you inhale helium, you are changing the type of gas molecules in your vocal tract and increasing the speed of the sound of your voice and changing the timbre. Your voice sounds higher pitched. In contrast, heavier gases like xenon and sulfur hexafluoride slow the speed of sound and lower your resonant frequencies.