Question: why are we on earth

Scott Melville answered on 8 Nov 2017:

Science is no good at answering questions about ‘purpose’, but it can tell us interesting things about ‘how’ things happen.
Humans have been able to evolve on Earth because it has the right mix of chemicals, like carbon and water. Importantly, we are not too far from the Sun (then all the water would be ice), or too close (then all the water would be steam). Only planets just the right distance from their star can have liquid water – this is called the ‘habitable’ (or ‘Goldilocks’ 😉 ) zone. When searching for other planets which we might be able to live on, we first check that they’re the right temperature (the right distance from their star) that water can be liquid, and then we look for any signs of elements like carbon. There are a few good candidate planets out there, which might have similar life, but no confirmed alien sightings yet!