This week, SciAm frequent contributor Charles Q. Choi spends his days in the Yukon on an expedition with researchers from the American Museum of Natural History in New York City. Their goal: to recover intact DNA from mammoths, which once roamed the tundra but went extinct some 11,000 years ago.
Slide Show: Mammoth Excavation Photos
[Click here to see his blog posts from the Yukon.]
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Below are excerpts from his posts:
DAY 1 June 13, 2008
Today I begin a dig in the Yukon! Ross MacPhee, the American Museum of Natural History's curator of mammalogy, and his colleagues are personally interested in finding mammoth DNA, either in bones or in frozen earth.
For our first day, we go to Paradise Hill, a site for gold mining for the past century or so, about 20 kilometers [12 miles] east of Dawson City. We drive right up to the site—a real luxury in field work—on curving, bumpy gravel roads, over wooden bridges, past abandoned, rusting mining equipment, surrounded on all sides by spruce forests mixed with paper birch and aspen trees, explained archivist Clare Flemming, an associate at the American Museum of Natural History and Ross's wife.
The excavation site is a wasteland of orange and brown gravel dotted with pinkish white quartz chunks. Geologist Duane Froese of the University of Alberta points out a bed of tephra, or volcanic ejecta, about 50 feet [15 meters] high on the walls of the site, which likely came from the Wrangell Mountains hundreds of miles away in southeastern Alaska.
Underneath the tephra bed is what the miners call "muck"—silt loaded with decomposing organic material from the Pleistocene, which reeks of an odor Froese charitably compares with a horse barn. Loaded in this muck may be the DNA that Ross is looking for (that is, woolly mammoth DNA from 80,000 to 100,000 years ago), as well as that of the plants, bacteria and other life once found here thousands to millions of years ago.
[Read more about how researchers extract samples and the technology used to date them.]
DAY 2 JUNE 14
Today we see bones. One tool gold miners here use for excavation is a water cannon, dubbed a monitor. Six weeks ago, as one miner named Jonathan was blasting away at the muck with cutting jets of water, he was quite excited to expose a slew of fossils—mammoth, bison, camel, horse (horses actually originated in North America), musk ox, caribou and what may be short-faced bear.
With the roar of the monitor behind us, we pick over skulls, tusks, vertebrae, limb bones, ribs, jaws—which Jonathan dried in rows in the sun—each like ivory pieces from dozens of nearly identical jigsaw puzzles. "The hills are alive with the sound of bones," Ross quips.
After looking over the bones Jonathan brought out, we go straight to the raw, exposed earth and pick over the rocks ourselves to look for fossils, stepping over the wet rocks and sticky gray muck and studiously avoiding the water jet. The monitor is not chained down right now, and if it were to sway we certainly would not like to be hit by a water jet powerful enough to cut through a hill. We turn up horse bones just freed from the permafrost that may very well contain intact DNA.
DAY 3 June 15
We have gone prospecting today, driving some 75 kilometers (47 miles) away from Dawson and deeper into the Klondike forest, passing snow and beavers.
We first stop at the largest operating gold mine in the Klondike, Ross Mine. This is a placer mine, meaning that the gold is hidden in sand and gravel deposited by modern or ancient streams or glaciers—the panning for gold carried out during the California and Klondike gold rushes is an example of placer mining. The mine manager shows us mammoth tusks they found, with full tusks ranging up to eight to 12 feet [2.4 to 3.7 meters] long, eight to 10 inches [20 to 25 centimeters] in diameter, and close to 200 pounds (90 kilograms) in weight.
[To read more of Choi's Yukon adventures, including what else he's found in the ice, tephra and muck, click here.]