Today, Let's visit North GrIP. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.
North GrIP stands for North Greenland Ice-core Project. An international, Denmark-led group began drilling through the ice in central northern Greenland in 1996. On July 18th, 2003, they reached the soil of Greenland, 1.9 miles below. They'd extracted a two-mile-long, four-inch-diameter, rod of ice.
New York Times writer Daniel Grossman tells how they're finding that the ice at the very bottom was laid down 120,000 years ago. They're able to read 120,000 winters on the ice core, the way they might read rings on a tree.
If old ice seems unexciting, look at what it contains: Rain and snow are only water. However, some of the oxygen in H2O is an isotope called oxygen-18 -- an oxygen atom with two extra neutrons. The fraction of this isotope depends on the temperature it was when it fell from the sky. That fraction has been frozen in place for millennia -- a record of temperatures waiting to be read.
We can visualize the Greenland ice cap as a huge shallow dome, two miles thick in the middle, and sloping off two hundred miles to the sea on either side -- just enough slope to let ice slide away in either direction. Only here in the center, where North GrIP is drilling, has there been no sliding, and history remains intact.
Much more information awaits us in this two-mile shaft of ice. As it took form, tiny bubbles of air were entrained into it. From those bubbles, we can read the past presence of heat-trapping gases like carbon dioxide and methane.
Other kinds of history also lurk here. For example, the large volcanoes of the past have left their marks. They emitted fine ash that circled the Earth and settled down upon the snowfields, before they were compacted into ice.
When the core-cutter finally reached bottom it produced yet another surprise. As team members pulled it up, they found it was heavier than it should've been. It emerged with a large icicle of brownish water, freshly frozen onto the bottom.
Geothermal energy warms the earth below this mantle of ice, which insulates the earth and keeps it warm. Water was still liquid below the ice. It froze only when it met the bit, which was very cold from its trip through the drill hole. That water could've been there since ice first formed over it. It could be far older, maybe a million years older, than the ice they drilled through. It might prove to hold evidence of ancient life.
The most ominous finding is that the ice ages have all been preceded by large, potentially destructive, temperature variations. We seem to be on schedule for another ice age, and wildly seesawing temperatures might be a greater threat than climate change alone.
So, like all good science, this project raises questions as fast as it answers them. But so much is at stake in these ques-tions. This is truly valuable science, if I've ever seen it.
I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.
D. Goldstein, Drilling Through Ice In Search of History. The New York Times, Science Times, July 22, 2003, pg. D2.
The North GrIP site