CREATION - Snowball Earth - page 101

Biologists aren't so very different from geologists, under the skin. Some of them have jumped
eagerly on to Paul's Snowball bandwagon, and some have declared furiously that it must be stopped.
And some are still waiting to see what will happen. Though the world of ancient fossils seems pretty
well explored, it's still possible that someone, somewhere, will find a vast stash of complex animals
from long before the Snowball. But in the absence of this, the evidence for some connection between
ice and new life is looking more persuasive by the day.
So biologists are beginning to think of ways that the Snowball might have triggered complexity.
Everyone agrees the capacity to be complex must already have existed in the creatures' genes, but
nobody knows for sure what spurred those dormant genes into action. The theories are not yet fully
formed; they're speculations in corridors rather than neat, tidy theories. But there are several intriguing
ways in which ice, that most inimical of substances, might ultimately have given rise to this new life.
The Snowball itself could have encouraged life to diversify and experiment. New species often
arise when a single population of creatures is separated from its fellows in an isolated refuge, for
something upwards of a million years. Or perhaps the opportunity for complexity arose after ice wiped
large areas of the planet clean of life. All living things need certain resources to survive—food, wa-
ter and shelter—and as long as enveloping mats of slime were hogging all the resources, there would
be no space left to innovate. Removing the extant occupants of Earth's ecological niches might have
made room for life to experiment. We already know that worldwide extinctions make space for new
species to emerge. When a meteorite wiped out the dinosaurs, for instance, the previously tiny mam-
mals suddenly had free licence to grow, change shape, and consume the resources once reserved for
the likes of Diplodocus and T. rex . Though there's no direct sign that the ice made any of the slime-
creatures extinct , it may have killed off enough of each species to create the breathing space that evol-
ution needed.
Another suggestion has come mainly from Jim Gehling. He wonders whether complex life was
a response to the sheer changeability of life in the Snowball's aftermath. First the world endured its
longest and most severe ice age, and then came a violent hothouse lashed with acid rain. With condi-
tions changing as drastically as this, life had a natural incentive to spawn creatures that could protect
themselves from external buffeting. Singlecelled slime balls are at the mercy of current and weather,
but large, multicelled animals have much more control. They can dig into the ground and hold tight
in fierce currents. They can control their internal temperature, store food more effectively against lean
times, and grow covers to protect themselves.
But the most popular idea for a trigger point involves oxygen. Large creatures need efficient ways
of mobilizing their food into energy, and oxygen is one of the best. When we breathe, the oxygen we
inhale is used to “burn” food, like burning petrol in a car engine, and that's what generates the energy
that supports our vigorous lifestyles. Oxygen is also necessary to make collagen— the connecting tis-
sue that binds muscles to bones and helps keep cells together, and that is found somewhere or other in
every complex animal.
There are some signs in the rocks that atmospheric oxygen was increasing around the time of the
ice. Perhaps whatever triggered the Snowball also created this excess of oxygen. Or perhaps there was
a sudden pulse of oxygen immediately after the freeze ended. For millions of years, life would have
been restricted to a few small refuges, and unused nutrients would have built the ocean up into a tasty
chemical soup. As soon as the ice was over, the few remaining creatures would have seized on these
nutrients and blossomed. The white planet would have become green with massive colonies of bac-
teria and algae stretching over the surface of the ocean. And those same colonies would have soaked