Over two billion years back in the past the Earth’s like a snowball with frozen white crusts.
The carbon dioxide levels were low which made our world colder and covered in snow.
Life had evolved as small single cells. But many would die as the temperatures fell.
Since some could survive that long glacier spell, could other ice worlds hide life-forms as well?
First published in Double Helix (Jul 2016)
Reproduced with permission of CSIRO