DOWN UNDER - Snowball Earth - page 67

SEVEN
DOWN UNDER
Paul Hoffman had woven together the Snowball story's different strands. His theory was new, but it
also rested firmly on observations and ideas from the past, especially those of Brian Harland and Joe
Kirschvink. With his carbonates and isotopes, however, he and Dan had provided the first evidence that
the Snowball might be right.
Now the theory was about to face its first serious challenges. They came, like so much in this story,
from the rocks of South Australia. After Joe had performed his magnetic magic on Flinders rocks in the
1980s, many other geologists had been back to poke at the outcrops, and prize out more of their data.
By the time Paul and Dan published their Snowball theory, there was already a stockpile of Australian
data just waiting to be mined. And from that data, two tests of the Snowball quickly emerged.
Since Nick Christie-Blick had become the main focus of much of the Snowball resistance, it's ap-
propriate that one of those tests came from his own research group. Ironically, though, the result didn't
conflict with Paul's theory at all; quite the contrary. Working in the Flinders, a student of Nick's had
already uncovered some evidence that turned out to be greatly in Paul's favour. She had addressed the
issue of timing. For Paul and Dan's explanation to work, the ice had to last many hundreds of thousands
or even millions of years, long enough for carbon dioxide to build up in the atmosphere and set the con-
ditions for the global layer of carbonates to form. So were they right? Just how long did the Snowball
last?
B ENNETT S PRING , S OUTH A USTRALIA, 1995
L INDA'S ARMS were already starting to ache. But she couldn't let go. If the drill doesn't go in straight,
the core is ruined and you have to start again. Water, milky with rock dust, was spurting out of the hole
and spraying her jeans from the thigh down; they were already clammy and soon would be sodden. She
shifted angle awkwardly, trying to rest her right arm on her knee. Even through ear plugs, the noise was
deafening.
To her right and left ran a dried-out stream cut, its steep walls casting her into shadow. Though Aus-
tralia was on the fringes of winter, the temperature had crept into the seventies. The sky was scattered
with bright cirrus clouds. Thirty yards to the right, splashes of brilliant green rushes marked a sluggish
spring—the only water in this parched country for miles around. Linda had surprised a grey kangaroo
there that morning; it had made its characteristic “shhht” sound of alarm and thudded hastily away. Here
and there along the stream were stately red river gums, leaves still green, grey bark peeling to reveal the
silver trunk beneath. One good reason not to camp in the stream cut—you never know when a gum tree
will decide to shed a branch.