Geoscience Reference
In-Depth Information
TEN
EVER AGAIN
To figure out whether the ice will ever return, we first need to know why it appeared in the first place.
What was so special about the Snowball times? Though the clues are scant, some evidence has emerged
from another, even older part of Earth's geological history. Joe Kirschvink, the sparky, inventive Caltech
professor who set much of the early Snowball rolling, has discovered that Paul's Snowball period wasn't
the only one.
South Africa, September 2000
Y
OU'D EXPECT
the Kalahari Desert to be dry and hot, and so it usually is. Even the place names around
here evoke its baking, insufferable summers—Hotazel, for instance, a remote mining outpost an hour
or two north of here. (The land surveyor who proposed the name back in 1917 had to use this phonetic
spelling because the authorities objected to his original suggestion: “Hot as Hell”.)
But now, at the tail end of a southern winter, the desert is both cold and very wet. The rain began
yesterday evening with a roar that eventually settled down into a night-long drumroll on the tin roof
of our tiny motel. It has turned the dirt road into a skating rink of rich, red mud. I'm here with Joe
Kirschvink, who has brought a phalanx of students to tour the geological sights of South Africa. As our
five vehicles lurch in convoy through the puddles, fountains of red water fly into the air and separate
out into thick, cartoonlike drops.
We turn, thankfully, on to a paved road again, and the rain begins to ease. The landscape in
the southern Kalahari is just like Paul Hoffman's Namibian field sites: open and almost featureless,
scattered with camel thorns and golden grasses and those towering red termite mounds, as tall as the
trees. There's a striped gemsbok, sheltering among the thornbushes. And there, hanging from a tele-
graph pole, is a familiar weaverbird's nest, an impressive sack of entwined grasses nearly five feet long
and almost as wide. The road begins to gain altitude, and the temperature drops further. A dense white
mist descends around us, hovering off-road just beyond the barbed-wire fence. At the designated road
cut, we climb out of the vehicles and wince as flecks of ice fly by in the freezing fog. But Joe is cheer-
ful. “What did you expect?” he says with a grin. “This is Snowball country.”
He's right. All around us, among thornbushes and orange clumps of grass, are the now-familiar
signs of ancient ice. The background flame-coloured rock is studded with pebbles and stones that were
once bulldozed along the ground by glaciers, and then tipped offshore into a shallow, ice-covered sea.
Not all of these have remained embedded. The sides of the road are scattered with loose pebbles and we
spread out, red-cheeked in the wind, seeking stones with tell-tale glacial scrapes. Here's one, a small
rounded lump, indented with parallel grooves where it was scoured along the ground. These deposits
bear all the hallmarks of a Snowball. Not just the jumbled, scratched ice rocks that we see here; back
