Geoscience Reference
In-Depth Information
But why did it take so long? The Slimeworld lasted for almost the whole of Earth history. Let's put
in some numbers. Our planet had been around for 4 billion years before the first complex earthlings
emerged from the ooze. That's nearly 90 per cent of Earth's lifetime.
Four billion years is an insane amount of time, almost impossible to contemplate. There have been
many attempts to capture this spread of time in ways that we can comprehend. If the history of life on
Earth were crammed into a year, slime would have ruled through spring, summer and autumn, continu-
ing well past Halloween into the beginnings of winter. If it were squeezed into the six days of creation,
slime ruled until six o'clock on Saturday morning. If it stretched over a marathon course, slime would
have led the field past the twenty-three-mile mark.
2
encompass all the time on Earth. Let's say that time runs from left to right, so Earth was born at the
tip of the middle finger on your left hand. Slime arose just before your left elbow and ruled for the
remaining length of your left arm, across to the right, past your right shoulder, your right elbow, on
down your forearm, and eventually ceded somewhere around your right wrist. For sheer Earth-grip-
ping longevity, nothing else comes close. The dinosaurs reigned for barely a finger's length. And a
judicious swipe of a nail file on the middle finger of your right hand would wipe out the whole of
human history.
Stephen Jay Gould set the discovery of these vast stretches of Earth time in a long line of findings
that put humans firmly in our place.
4
Galileo, said Gould, taught us that the Earth isn't the centre of
the universe. Darwin, that we're just another kind of animal. Freud, that we're not even aware of most
of the things going on in our own heads. And geologists have now discovered that the Earth reached
late middle age before we were so much as a glimmer in its eye.
Though we humans are certainly complex, also clever, perhaps even the highest form of life that
Earth has so far produced, we're nothing like the most natural earthlings. Measured in units of staying
power, Earth's first, most primitive experiment in life was also its best. With simple individual cells,
nothing complex, nothing flashy, each creature out for itself, life had found a supremely winning for-
mula. Why should it ever change?
That's the question that has plagued complex, clever, thinking, adaptable humans since they first
uncovered this bizarre history of life. Earth looked set to stay locked in slime for ever. Why did com-
plex life appear at all, and why did it wait to emerge until that one point in time, just a few hundred
million years ago, nearly at the end of the marathon, somewhere near your right wrist, late in the
Earth's middle age?
To answer this, Paul Hoffman has seized on an idea that was first proposed sixty years ago, and
was then dropped, half-heartedly resurrected, and dropped again several times over the intervening
years. There's nothing half-hearted, however, about the resurrection Paul has now effected. He's mar-
shalled new evidence, restored and amalgamated old ideas, and employed fierce argument to persuade
the people around him. According to Paul, life's richness, diversity and sheer overwhelming complex-
ity arose from a mighty catastrophe. It's called the “Snowball Earth”.
F
IRST CAME
the ice. It crept from its strongholds at the North and South Poles, freezing the surface of
the ocean, spreading gradually over the Earth's surface. A blue planet inexorably made white.
Individual crystals of ice first appeared in the sea like tiny floating snowflakes. They were smashed
together by wind and waves, their fragile arms broken and their debris turning the seawater into a
