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SciAm frequent contributor Charles Q. Choi writes from 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. See Choi's first blog post from the Yukon here. DAY 2: June 14, 2008 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. Ancient streams likely collected all these bones together in a creek, Duane suggests. As the climate later cooled, the vegetation all changed, making hill slopes unstable. They rapidly buried the bones under sediment, where they remained unseen until the monitor came"”water concentrated the bones together, and now water is revealing the bones to the world again. 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. Nearby is an old log shaft that a miner built and abandoned long ago while hunting for gold"”the same water that concentrated these bones likely concentrated gold as well. The monitor is going to blast downward at least another 20 feet looking for gold, and it should turn up more fossils as well"”treasure of a different kind. * Today we are also joined by tephra chronologist Britta Jensen from the University of Alberta, who is here to practice sifting techniques with Svetlana Kuzmina in preparation for upcoming fieldwork in Alaska. We finish digging and sifting at Paradise Hill. Duane gets some geomagnetic samples"”seeing if the magnetic alignment of particles in the sediment here matches the current magnetic alignment of the Earth. If it doesn't, that means these silts pre-date the last major reversal in the Earth's magnetic field, some 780,000 years ago"”one method by which to date the excavation here. * At the end of the day, over beers, we join the mine owners at their log cabin home to look at a bison skull the monitor exposed. It experienced curious damage on it, almost as if a blade had driven into the forehead but later healed over. We joke the wound came from an arrowhead, although the skull almost certainly pre-dates the arrival of humanity in North America by thousands of years. Ross and Clare clean the dirt off the skull while debating whether the damage was caused by, say, a falling rock, or was perhaps congenital in nature. There do appear to be abnormalities that may have been caused by defects during development, although they might also have been caused by infection following injury. It's the familiar interplay among scientists debating over interpretation of evidence"”and between husband and wife.