There is twelve times as much helium in the universe as all the other elements (except hydrogen) combined, but it’s one of the rarest elements on Earth.
It is so light that it floats to the very top of our atmosphere and diffuses into space, so most of the helium we have on Earth (including every helium balloon you’ve ever held) has recently come from the radioactive decay of uranium and other radioactive elements.
Despite this it’s completely safe, as helium has a couple of chemical superpowers.
The first one is that it’s ‘inert’. This means there’s practically nothing you can do to it to make it react with anything else, so it cannot harm you in any way.
It’s second superpower is that no matter how cold you make it, it’ll condense into a liquid but it will never freeze.
These are some unique superpowers, so we use helium for a range of special tasks.
When we’re manufacturing extremely sensitive equipment, like fiber optic cables and semiconductors, they can react with gasses in the atmosphere. So when we’re making these things, we make the factory airtight, and swap the normal atmosphere with inert helium.
Also, things that need to be extremely cold to function like MRI scanners and particle accelerators are cooled by liquid helium. The study of this field is called ‘cryogenics’.
Of course, helium is also used in balloons. In the same way that oil floats on water, helium balloons float on air.
This happens because air is a mix of nitrogen, oxygen, hydrogen, carbon dioxide and other gasses, and helium is lighter than pretty much all of them.
When you let go of a helium balloon and it soars into the sky, it will slowly deflate over a few days as the helium escapes through tiny holes in the rubber balloon.
Eventually the balloon will settle back down to the ground, while the helium that was inside will rise to the top of Earth’s atmosphere and pass through the edge of space, never to return to the Earth.