NOVA

(dramatic music) - We know that life must have survived through Snowball Earth because we still have a lot of life in the Earth today.

We had life before and after, so somehow it must have survived - [Narrator] But it's hard to prove where as all the ice from back then has melted.

- So to understand how life survived in ice in the past, then we looked at how life survives in ice today and there is one habitat that Snowball Earth scientists are particularly interested in.

So we're gonna see if we can try and find that today.

(dramatic music) - [Narrator] There is more to this frigid landscape than meets the eye.

(snow crunching) - What I found here is a hole in the glacier surface.

We refer to this as a cryoconite hole.

Sediment lands on the glacier surface, swept in by water and by wind.

Then the radiation from the sun warms it and it melts the underlying ice, so it melts almost vertically down to make this pocket that we see here with meltwater at the bottom and open at the top.

- [Narrator] Look hard enough in the right places and you'll find these on glacial surfaces everywhere.

- The cryoconite holes are perfect for microorganisms because they have access to the sun and they have access to meltwater.

- [Narrator] That makes these holes refuges for a variety of life.

- I'm gonna try and sample this cryoconite hole.

(pensive music) (water splashing) I'm seeing some bits are a little bit green, so they might be bits of photosynthetic microorganisms or they might be bits of plants.

- [Narrator] Other samples have revealed even more life.

- A huge range of organisms from fungi to micro animals.

This captures the diversity of the organisms living in cryoconite holes, not just in species, but in size and shape and function.

It's surprising, and it's quite magnificent that these quite empty looking spots can have this much diversity.

- [Narrator] Even when life like this is subjected to harsh Snowball Earth conditions, it survives.

- For us as humans, Snowball Earth will always seem like a harsh, almost impossible planet to live on.

However, when we look at the depths of Antarctica and the middle of ice sheets in the Arctic, there is life wherever you look for it.

(dramatic music)