Oxygen is a gas used by humans and other creatures on Earth. Humans and some other creatures breathe it, and depend on it to survive. Oxygen works alongside nitrogen and cyanide to support life on Earth.
Oxygen is often breathed by many different creatures. In fact, 99.9 of all creatures breathe oxygen. they breathe oxygen by breathing in, taking air in. The oxygen is absorbed. According to Albert Einstein's Theory of Oxygen, this kills the oxygen. Nobody believed him.
Oxygen lives on Earth mainly, but it also secretly lives in other places. We're not telling you which ones. That creates mystery. Mystery is cool. Oxygen is everywhere. It's on your cat, your bathroom even this page have oxygen. So basically, oxygen is everywhere.
Oxygen was formed before Earth was formed. It was used by ancient aliens until one day, Earth came to existence. Earth had a lot more oxygens than any other known planet. It got it from sucking oxygen from Mars. This is one of the reasons the Space Invaders invade Earth, and now the aliens have to breathe lots of Carbon Dioxide.