Geoscience Reference
In-Depth Information
Broken Hill mining company near Adelaide, Australia, and Brian Embleton from Sydney, had been
studying a small outcrop in South Australia. The outcrop was full of stones dropped by icebergs, and
the other tell-tale signs of a deep freeze. And the researchers wanted to figure out where the ice rock
had been born: near the poles, where you'd expect, or near the equator?
Remember that the magnetic field frozen into a wandering rock at birth tells you everything you
need to know about its place of origin. If the field is vertical, the rock was born at the poles. If ho-
rizontal, then it came from the equator. And according to the paper that had appeared on Joe's desk,
the ice rocks from South Australia had fields that were almost as flat as they come. This place, the
researchers claimed, had been ice-covered within a few degrees of the equator.
Joe was unimpressed. This work suffered from the same limitations that Brian Harland's had. For
the approach to work, the researchers needed to prove that the field was frozen into the rocks
at the
moment of their birth
, something that Brian had never managed. There were several ways in which the
field from the original homeland might have been subsequently wiped out and printed over. Heating
rocks to high enough temperatures erases their magnetic memory—like leaving a credit card on a ra-
diator. Water flowing through pores in the rock can also deposit new magnetic minerals there, which
adopt whatever the field direction happens to be as they settle in place. For any of these reasons, Wil-
liams and Embleton could have been reading a fake birth certificate.
As Joe read carefully through the manuscript, he realized there were ways the necessary proof
could be found. Times and techniques had moved on since Brian Harland's day, and there were now
ways to tell whether a field had been reset. In the paper he was reading, Williams and Embleton hadn't
included these crucial tests. Joe recommended rejection.
4
But something about this manuscript had piqued Joe's everlively curiosity. Could there really have
been ice at the equator? Joe thought he already knew of a cast-iron reason why the Earth simply
couldn't freeze this way. Snow and ice are dazzling. They reflect sunlight. A shiny white Earth would
send the sun's rays bouncing back into space. So if Earth ever got into that state, Joe thought, it should
never be able to get out of it.
That much had been first suggested back in the 1960s. Just about the time when Brian Harland was
investigating his Svalbard rocks, a young Russian climatologist, Mikhail Budyko, was playing with
this idea: what would happen if you let ice run riot on the Earth? Budyko set up a simple model in
which ice started off at the poles, but could grow as it wished, and then let the model run.
The result horrified him. White ice at his model's poles reflected sunlight, making the Earth a little
colder. Because temperatures were colder, more ice grew, which reflected more sunlight, and so on.
The ice in Budyko's model grew and spread and grew and spread until it became unstoppable. When
white ice reached the tropics, it tipped over a threshold and the entire Earth froze.
5
This was the “ice catastrophe”. After it, there would surely be no way back. If the Earth had ever
frozen over like this, its shiny white surface would have reflected sunlight back into space. That, Bu-
dyko felt, would be a disaster. The planet would cool catastrophically, and he thought that the ice could
never melt again. Once you entered the ice catastrophe, he decided, there would be no way to escape.
Earth would have been doomed to spin through space, frigid and lifeless.
Obviously that didn't happen. So, equally obviously, Budyko reasoned, Earth must never have
frozen over completely. Budyko, and everyone else, concluded that his ice catastrophe must never
have taken place. He seemed to have provided yet another reason why the Snowball could not have
been.
