SNOWBRAWLS - Snowball Earth - page 85

have survived the Snowball: bacteria, of course, in their enveloping mats of slime; slightly more soph-
isticated—but still single-celled—creatures, with their internal chemicals neatly packaged rather than
floating freely in a soup; simple algae, brown and green and red. All these creatures left their faint
fossil traces in rocks from both before and after the ice, so they, at least, must have lived through it.
But the scale of Paul's freeze-over was troubling. If it was as severe as Paul insisted, how could any-
thing have remained alive at all? This was to become the Snowball's next test.
I CE IS an extraordinary substance. Subtle shifts in its structure can render it white or green or blue,
translucent or opaque. It can shatter like glass, or creep like treacle. Ice is a tough building material,
as strong as concrete. In the Second World War, plans were even developed to create giant aircraft
carriers called “bergships” out of ice. They might have been built, too, if the range of aircraft hadn't
increased enough to render them obsolete. Russian empresses used ice to build vast, glittering palaces:
“The delightful material gave a new, fantastic beauty to every feature, sometimes white and sometimes
clear green—dark and opaque where the shadows fell, and almost transparent in the sun. No dream
castle of jasper or beryl . . . could be more beautiful than these wonderful buildings of ice.” 7
Ice is alien to life. Part of the attraction of the Antarctic ice cap is that the essentials of life—food,
water, fuel and shelter—have all been stripped away. Explorers have talked for decades about the sub-
limity and purity of this landscape. “During the long hours of steady tramping across the trackless
snow-fields, one's thoughts flow in a clear . . . stream,” Antarctic explorer Sir Douglas Mawson wrote,
while trying to explain his urge to return. “The mind is unruffled and composed and the passion of a
great venture springing suddenly before the imagination is sobered by the calmness of pure reason.” 8
But there is danger as well as purity in this escape from life. Remember Wegener in Greenland,
Scott in Antarctica, and Hornby in the bitter winter of the Canadian Arctic. Ice also kills. Every cell in
your body is a squashy bag of water, with just a few other chemicals thrown in. If this water freezes,
jagged crystals of ice appear, and they slash and tear at the cell's fragile walls. These membranes also
spring leaks when their molecules begin to congeal together into clumps, like fat cooling in a frying
pan. Within the cell, proteins unwind their complicated loops and become flaccid. With great care,
and clever technology, certain cells can be preserved on ice—sperm, eggs or bone marrow. But for the
most part, life depends on water; and ice brings death. 9
That's why the biologists were so worried by Paul Hoffman's Snowball. If ice covered the world,
how could even single-celled life have survived?
Water wasn't the whole problem. The oceans in Paul's world wouldn't have frozen solid, largely
thanks to another strange property of ice. Most solids don't float. They become denser when they
freeze, and in a bath of their own liquid, they'll sink. But ice is the exact opposite. When water turns to
ice, its molecules become more loosely bound, forming a lacy network that's full of space. That's why
ice floats, and why the Snowball oceans didn't freeze completely. If icebergs sank, lakes and oceans
would freeze from the bottom up, instead of just growing an ice skin on their surface. So, even as Paul
envisioned it, there would still have been plenty of liquid water within the Snowball oceans.
But living things also need sunlight. Because Paul argued that the entire surface of the ocean was
frozen over, all the water would be beneath that ice layer, blocked from the sun. And for most of the
simple denizens of the Snowball, darkness would mean death. Even the creatures that didn't make
their living using sunlight depended on the ones that did. Living things needed both liquid water and
sunlight, and for that, the ice had to have holes.