Geoscience Reference
In-Depth Information
thing roamed anywhere. When the Snowball gripped the Earth, the only living things hereabouts, and
anywhere else in the world, were those tiny, single-celled sacs of chemicals bound together by ex-
truded slime.
Though Death Valley is full of Native American trails, it wasn't seen by white men and women
until the mid-nineteenth century, when the first pioneers passed through on their way to hunt for Cali-
fornia gold and glory. Its moniker is unfair. The valley wasn't so dangerous, even in the early days,
if you could find the waterholes. Few people died here, though many had miserable crossings. The
landscape is bright with sand and salt and sun. And in spite of the generations of geologists who have
picked over the valley in the past century, it is still a place of geological mysteries. Like the migrating
boulders of Racetrack Playa, a dried-out lake bed to the north and west of Bad Water. The floor of this
valley is strewn with rocks of every size: pebbles, stones and vast boulders weighing seven hundred
pounds or more. And, inexplicably, these rocks move. Try to catch them at it and they will just lie
there, solid, immovable and innocent. But between visits from the geologists who carefully plot their
positions, these restless boulders somehow skid along the valley floor, twisting, turning, zigzagging,
and leaving grooved trails behind them. There have been many attempts to explain this bizarre Death
Valley phenomenon. Some people think the culprit is an intense gust of wind occasionally funnelling
through the valley; or a sudden rainfall that coats the mud with a slippery sheen; or thin sheets of ice
that lift the boulders and make it easy for them to slide. Nobody really knows.
The trucks turned west now, where a wide sweep of open land sloped toward the sand dunes in
the centre of the valley. Except for the small pools at Bad Water, the valley floor was bone-dry. But
up over the western mountains, occasional snow clouds hovered like pale will-o'-the-wisps, trailing
off at their base where the snow evaporated before it ever hit the mountain surface. As Martin's truck
wound gently up the road through Emigrant's Canyon to the mountain pass, a few fat flakes of snow
smacked the windscreen.
Over the pass, walls of rock stretched upwards at the roadside, speckled with coloured rocks and
boulders. This was the Kingston Peak diamictite, a direct remnant of the Snowball. The mismatched
mélange of rocks had tumbled into the ice-covered seas of Snowball time and left behind a deposit
more than two miles thick. Glancing at the rocks, Martin began to get annoyed. “How could you get
all this in the final days of the Snowball?” he demanded, gesturing out the window. “If you believe
Paul's Snowball, all this was deposited in a thousand years or so. You just can't get sedimentation rates
like that!”
This was part of an ongoing argument. In recent months, many people had been wrestling with the
question of when exactly the ice rocks had formed. Was it only at the end of the Snowball, or were
they continuously created throughout the previous several million years that it gripped the Earth? It
mattered because of thick deposits such as these. Everyone agreed that they were created when glaci-
ers gathered up rocks and dragged them to the sea, or when icebergs melted on the water and dropped
their load of debris on to the mud below. But in the first incarnation of Paul and Dan's Snowball idea,
this couldn't have happened during the long, cold millennia of the Snowball. When the oceans are
frozen over, icebergs can't break off and move around, because there's nowhere to move to. And with
frozen oceans, it's extremely hard to get ice on the land. To make a land glacier you need snow, and
to make snow you need some patches of open water to deliver the moisture. At first Paul and Dan
believed that the Snowball would have been cold, dry and dead, with no snow, no glaciers and no ice-
bergs until, perhaps, the very final days when the ice began to melt back.
Then how to account for two vertical miles of rock? Martin was right—you couldn't get such thick
deposits from such a short time. But Paul's Snowball idea had evolved since he first started working on
