Question: why is earth the only planet that humans live on?

Kate Elliott answered on 9 Nov 2016:

Good question! Life (or at least life as we know it) is very sensitive to it’s environment. Humans like certain temperatures and an atmosphere we can breathe. We need food and different elements to build things with. We also need to be protected from the harmful x-rays from the sun (the ozone layer does this). When the earth was formed we were lucky that it was in a place that was not too hot or too cold, that it had a rich and varied number of chemical elements but not too many dangerous ones. It’s kind of like the Goldilocks planet and everything happened ‘just right’ so that life (and then humans) could survive and flourish!