Depending on where you stop defining ‘earth’, it’s either Iron or Oxygen – and both are pretty common! The benefits of oxygen are obvious – without it, we wouldn’t be able to survive. Iron also has lots of uses, both biologically and not. It’s present in all of our cells, and helps in the delivery of oxygen around the body. It’s also involved in enzyme reactions in various tissues. Other than that though, we also use iron to make things like tools and buildings, that help us to do countless other things! So they’re both pretty important!