EUREKA - Snowball Earth - page 52

air in the ice to be measured, too. Want to know precisely what the prehistoric atmosphere was like?
Look no further. Here in this bubble is a whiff of air that was last breathed by Homo erectus , and was
trapped and buried long before the Neanderthals ever appeared.
In temperate zones there's not much ice to be had. But researchers can at least study the thickness
of tree rings. They don't even have to chop the trees down. They carefully bore into the side of the tree
and pull out a thin core of wood, about the size of a drinking straw. And then they just need to count
and measure. A thick ring? That was a wet summer. A thin one? Must have been dry. If they pick big
enough, old enough trees, researchers can build up a climate record going back hundreds of years.
Dan, however, takes a different approach. His obsession is the tropics, where ice caps occur only
on high mountains, and trees don't tend to grow annual rings because one season is pretty much like
another. Instead he seeks out the climate records hidden inside giant corals. Like trees, corals lay down
a new growth ring every year, but their rings are made of carbonate rock rather than wood. Measure
the growth rings year by year, and you can learn how the climate of the tropical ocean has changed. If
the coral is big enough and old enough, its rings can take you back hundreds of years. Find an ancient,
fossilized coral, and you might even learn about the tropical climate from thousands of years ago.
When Dan dives for samples, he carries along his scuba gear, lift bags and a huge, one-hundred-
pound drill. Even underwater, that's heavy. You dive in pairs. One person kneels on the coral with the
drill; the other holds on to the rest of the equipment. The noise from the drill is so overpowering that
you can hardly hear yourself breathe. When you're drilling, the fish keep well away. A fine powder
gradually emerges from the edges of the drill hole, floats over the coral surface, and then disappears
into the surrounding water. You stop every so often to add an extra length of tube above the drill bit.
You wear thick knee pads to keep your wetsuit from being cut to pieces by the coral's spiky surface.
Sometimes there are strong currents. You have to wear extra weight belts and try to anchor yourself on
to the coral, and the sensation is like trying to drill the road during a hurricane. Sometimes the coral is
deep, say sixty feet or so below the water, and you have only about an hour of air to land on the coral,
drill a core, heave the drill up again, and race back to the surface. But if the coral is shallower you
can take your time, enjoy the scenery, sneak some moments when you've finished drilling to wedge
yourself in among the corals and sponges and watch the fish go by. 2
Though Dan had never worked on rocks as old as Paul's, he had spent plenty of time studying cor-
als and unlocking their carbonate secrets. And his insights into Paul's mysterious Namibian carbonates
were about to prove crucial.
H ARVARD , S UNDAY , 15 F EBRUARY 1998
P AUL COULD still feel a slight ache in his legs as he sat at his desk in Harvard. The Boston Marathon
was coming up in a couple of months, and he had upped his training levels. Yesterday he had run al-
most twenty-two miles. Now, though, he was back in his office. He had worked through the evening
and it was getting late, but he still didn't feel like going home.
That's when Dan wandered in, with a friend who was giving a seminar at Harvard the next day.
“Come and meet Paul,” Dan had said, over dinner. On a Sunday night? At this time? Oh yes, no prob-
lem. Paul will be there.
Dan wanted to talk to Paul about his Namibia paper. Paul had handed it to him a couple of days
earlier. He'd scanned it, and felt annoyed because the interesting part seemed to be buried right at the
end. As soon as Paul asked him about the paper, Dan waded in. You want to know what I think? This