It's known that the Earth almost certainly went through a period of global glaciation billions of years ago - but it's never been clear how life managed to survive.
But, says Adam Campbell, a University of Washington doctoral student in Earth and space sciences, the answer could be thatlife managed to cling on in a long, narrow body of water something like the Red Sea.
The Earth is believed to have become a giant snowball at least twice between 800 million and 550 million years ago, with each episode lasting about 10 million years.
This was before the Cambrian explosion about 530 million years ago, when life on Earth rapidly expanded, diversified and became more complex.
But simple photosynthetic plankton turn up in the fossil record both before and after the 'snowball Earth' events - tricky, if the oceans were completely encased in ice.
It's assumed the algae survived these episodes, "unless they re-evolved each time, which creates a whole different problem for evolutionary biology," says Campbell.
"Under those frigid conditions, there are not a lot of places where you would expect liquid water and light to occur in the same area, and you need both of those things for photosynthetic algae to survive."
But, using an analytical model that applied basic principles of physics to a simple set of atmospheric conditions believed to have existed at the time, Campbell has concluded that a long, narrow body of water such as the Red Sea could have remained as open water.
A body about 6.5 times longer than it is wide would create enough physical resistance to advancing glacial ice that the ice sheet wouldn't make it all the way to the end of the sea before conditions caused it to turn into vapor. That would leave a small expanse of open water where the algae could survive.
"The initial results have shown pretty well that these kinds of channels could remain relatively free of thick glacial ice during a ‘snowball Earth’ event," Campbell says.
The open water in such a sea wouldn’t have lasted long if it wasn't somehow being replenished – if, for example, the glacial ice acted as a dam and cut off the influx of additional sea water. After all, the open water had to exist for around 10 million years for the algae to survive.
The full paper's here.