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.
(Theme music)
D. Goldstein, Drilling Through Ice In Search of
History. The New York Times, Science Times,
July 22, 2003, pg. D2.
See also the following website for more about North GrIP.
The North GrIP site.
The Engines of Our Ingenuity is
Copyright © 1988-2003 by John H.
Lienhard.
