Geoscience Reference
In-Depth Information
was ice in New York then, but none in Mexico. If you were in northern Europe during one of those ice
ages, you shivered. But if you were in the tropics, you scarcely noticed.
Instead, Paul's Snowball was the coldest, most dramatic, most severe shock the Earth has ever ex-
perienced. It was the worst catastrophe in history. For perhaps a hundred thousand centuries, Earth
was a frozen white ball, desolate and all but lifeless.
To the microbes, the Snowball must have seemed like the end of the world. Some survived, of
course—they must have, or we wouldn't still see them today. Perhaps they huddled for warmth around
undersea volcanoes. They might have survived near hot springs, or found fissures and cracks in the sea
ice where the sun's rays could slip through. But for many, perhaps most, the Snowball was disastrous.
Eventually the Snowball empire began to founder. Volcanic gases gradually built up in the atmo-
sphere, trapping the sun's heat and turning the air into a furnace. After millions of years of stasis,
the ice finally succumbed, melting in a rapid burst of perhaps just a few centuries. Temperatures now
soared to 40 degrees C. Intense hurricanes flooded the surface with acid rain. Oceans frothed and
bubbled, and rocks dissolved like baking powder. Earth had leapt out of the freezer and into the fire.
There was at least one more of these Snowball-inferno lurches, and there may have been as many
as four. But at the end of them all, after the last of the Snowballs and its attendant hot-house finally
faded, some 600 million years ago, came the most important moment in the history of evolution. The
rocks that appeared immediately afterwards bear fossils showing the first stirrings of complex life. Out
of the ice and the fire that followed had come the complexity that we see around us today.
T
HIS IS
Paul Hoffman's vision, and he is enchanted by it. Most other geologists are horrified. Accept
his story, they say, and you have to reconsider everything you thought you knew about the workings of
the world. Geologists are taught from an early age that the Earth is a slow and steady place. The past
looked pretty much like the present. Change happens only very slowly, nothing is terribly extreme.
True, there have been a few occasions where they have been forced to admit, somewhat grudgingly,
that this picture falls short. The idea that an asteroid came from space to wipe out the dinosaurs was
once derided, but is now widely accepted. OK, the argument goes, so the occasional extraterrestrial
calamity can rock the Earthly boat. But broadly speaking, the geological picture of Earth's history is a
settled, safe, comfortable one.
Compare that to Paul's picture of the Snowball. A global freeze. A planet that looked more like
Mars than home. Ice
everywhere
. And then a sudden lurch from the coldest to the hottest that the Earth
has ever been. Every way you look at it, his Snowball stretches the bounds of decency. It's as extreme
and catastrophic as they come.
Small wonder, then, that the Snowball has become the most hotly contested theory in earth science
today. Paul Hoffman, though, is resolute. He is the chief champion of the theory. By argument, evid-
ence, and brute force of personality, he is determined to win over the unbelievers.
Paul is an obsessive man espousing an extreme theory. If he is proved right, we'll have learned
something important about where we all ultimately come from. But there's a darker side to Paul's the-
ory. He has uncovered behaviour in our planet that's unsettling in the extreme. If his vision is true,
Earth can experience sudden lurches in climate that are more violent, and deadly, than anyone had ever
imagined, and such catastrophes may well happen again.
