2.1  Why are atmospheres important?

What a planet’s atmosphere consists of is very important if we want to understand the conditions prevailing on a planet. For example, the principal gases in Earth’s atmosphere are essential for life as we know it. Nitrogen is the most abundant, and is a key chemical in our cells and in plant cells. As a gas in the atmosphere nitrogen is very unreactive, so we rely on special bacteria to convert it into a form that other life can use.

Around a fifth of the Earth’s atmosphere is made of the gas oxygen. Plants produce oxygen, which humans and other animals then inhale – without it, we couldn’t survive. Scientists think that finding oxygen in another atmosphere could be key to finding another planet that hosts life, and you will revisit this idea next week.