EUREKA - Snowball Earth - page 48

stopped when he realized I wasn't with his group? Confront Paul at your peril. Criticize him head-on,
and his temper will flare. How dare I, he responded. It was my responsibility, not his. I should have
let him know I was following him. (But this had been his plan, not mine. And who else would I have
been following? How else would I have reached the outcrop?)
I stalked off to look at the rocks. They were beautiful, a delicate rose colour, and as I watched the
sinking sun spill on to them, I tried to calm myself down. What's the point of letting it get to you? You
know what Paul's like. He dishes this out to everyone. It's nothing personal. By the time I returned,
Paul was wreathed in smiles again. He congratulated me on having acquired the day's best campfire
story and offered to show me, as we walked back, the baboon skull he'd found on the way. He was
charming and I was soothed. And I'd had my first taste of the strangely mixed experience of working
with Paul Hoffman.
P AUL SAW the ice rocks everywhere he went in Namibia. He sought them out, and they intrigued and
confused him. The rocks had formed in a Precambrian shallow sea, and though each outcrop was
different, all bore the distinctive signs of ancient ice. Some contained lone boulders that had been
dropped by icebergs floating overhead. Some contained the mad jumble of rocks and stones that had
been scraped off the nearby land by glaciers, and bulldozed into the sea. Occasionally these jumbled
rocks bore scrape marks where the ice had dragged them over the ground.
Some deposits were hundreds of metres thick, while others were just a thin skin. Many were also
capped by a mysterious layer of carbonate rock, which had often turned pink, or perhaps ochre, with
the touch of wind and weather. Paul, like Brian Harland before him, was baffled by this. Carbonates
usually show up in warm water, in the tropics, but these appeared immediately after ice. And the con-
tact between the glacial rocks and the carbonates was always knife-sharp, as if there had been some
sudden, dramatic change from ice to tropics, from cold to hot.
After the summers mapping the Namibian ice rocks, Paul spent his winters puzzling over them
back home. At the end of each season he brought samples to Harvard, and stared at the rocks in his
office. He crushed them and measured them in his lab, all the time wondering what story they had to
tell. Then one day, he remembered that odd conversation he had had with Joe Kirschvink years earlier
about his “nutty” Snowball Earth idea.
Off to the library Paul went, to look up Joe's work on the Snowball. There was little enough, just
that one short paper buried in a vast, obscure topic. Paul read the paper and was gripped. He quickly
dug out Brian Harland's research, and the magnetic work by George Williams, and Mikhail Budyko's
papers about the ice catastrophe. He couldn't get enough of the Snowball. This was a story indeed. But
each of the proponents of the Snowball had dropped it, one by one, starved by lack of evidence. What
if Paul could provide the evidence? What if his Namibian rocks held the clues to this extraordinary
catastrophe?
Now Paul started looking directly for Snowball evidence, not in the ice rocks themselves, but in
the carbonates that bracketed them below and above, geologically before and after. Geologists have
many possible tools for extracting stories from stones, and one of the best involves measuring the ratio
of their isotopes—heavy and light versions of the elements they contain. Carbonate rocks, for instance,
contain different isotopes of carbon. There's a lightweight version called carbon-12, and a heavier one
called carbon-13. Comparing the ratio of the two can usually tell you something about the seawater
that the rocks were formed in. And when Paul looked at the lab results from his Namibia samples, he