21. An Ozone
We may not exactly need the ozone Earth has on a planet we go to, but we need something that can do similar things to it. Ozone itself is a gas that can be considered toxic but has powerful oxidizing properties. Earth’s Ozone Layer plays a critical role in our lives.
We have it in our stratosphere, where it shields us from the sun’s ultraviolet rays. This allows us to not burn up literally as we go outside. Essentially, it keeps the Earth from overheating. This is why the ozone layer is so often brought up in climate debates. We obviously need something like this on our new planet too.