JUDY WOODRUFF: Finally tonight: the story of a very big and very old find by archaeologists in Colorado. NewsHour correspondent Tom Bearden reports.
TOM BEARDEN: For the past month, employees of the Denver Museum of Science and Nature have been downright giddy. They have been digging up a treasure trove of some 500 bones dating back to the last Ice Age.
KIRK JOHNSON, chief curator, Denver Museum of Nature and Science: The table is covered with wrapped-up fossils.
TOM BEARDEN: Kirk Johnson, the chief curator of the museum, says they are between 45,000 and 125,000 years old. You seem pretty excited.
KIRK JOHNSON: I spent the last three weeks in -- up to my knees in mud digging out bones at 9,000 feet in the Colorado Rockies, where it was snowing. And it was one of the happiest times of my life.
I mean, we were finding bones at the rate of about every two -- two to 10 minutes. And the fossils were pouring out of the ground. And almost everything we found was something new. For a period of about six days, we were finding a new species of animal every day.
TOM BEARDEN: In that short time, the scientists discovered a juvenile mammoth, a Jefferson's sloth, at least five mastodons, and a bison skull with a seven-foot horn span. It's one of the richest single sites ever discovered in Colorado and at an extremely high altitude, nearly 9,000 feet.
KIRK JOHNSON: We know almost nothing about what happened at high elevation during the Ice Age. And that's one of the things that makes this site so cool is that not only is it a high elevation, but there's a fairly large thickness of sediment that has fossils in it. And the fossils are extremely pretty well-preserved. So, it's like a crystal-clear window back into a time for which we knew nothing at all.
TOM BEARDEN: Paleontologist Ian Miller says it's not just big animal fossils that make it so exciting.
IAN MILLER, paleontologist: There's all kinds of plant and insect and invertebrate fossils at the site as well that really helps us flesh out this ecosystem. And it's rare to get all of that in one place. Normally, we piece those things together from different areas.
But this site -- the preservation is so exceptional at this site, we're getting the fauna and the flora.
TOM BEARDEN: The first bone was discovered just a month ago by a bulldozer operator working on a reservoir expansion project for the Snowmass ski area near Aspen.
IAN MILLER: He knew that the bones were unusual. And one of the foreman on the site brought the bones home and identified on the Internet. And they called us in the morning, and they knew they had something special.
TOM BEARDEN: The museum immediately dispatched a team of 40 people to work alongside the construction crew to dig out the bones before the winter snowstorms hit.
KIRK JOHNSON: The bones had been buried in wet lake sediments since they were deposited more than 45,000 years ago. And that means they come out of the ground wet. Some of the bones are like solid sponges. And we found that, when you picked the bones up, they would drain clear groundwater. Like, a leg bone might give you a gallon of water. It was incredible. They just surge water.
TOM BEARDEN: The scientists quickly wrapped fragile bones in plaster and others in plastic to preserve the moisture. If they dry out too fast, they shatter. Back at the lab, the fossils were unwrapped, photographed, and catalogued. Once they have been dried, the real studies will begin.
KIRK JOHNSON: So, that's a classic. You can see the growth rings in that thing.
TOM BEARDEN: Johnson is particularly excited about the nearly two dozen mammoth and mastodon tusks they have recovered.
KIRK JOHNSON: These things have growth rings in them, so you can actually tell how old the animal was when it died. And the growth rings are put on, on such a regular basis, you can actually tell which season of the animal -- or season of the year the animal died in.
The tusks end up being sort of like a tape recorder of the animal's life. You can tell if the female had had calves or not, if the males had been fighting, lots of interesting things about the life history of the animals embedded in the growth rings in these tusks.
So, what we will do is carefully dry the tusks out, and then we will section them, and we will -- they will basically tell a story for each that was animal buried here.
TOM BEARDEN: And Johnson says these bones are likely to do more than just provide a look back at the Ice Age. They could provide clues to the future.
KIRK JOHNSON: Think about it. The Ice Ages -- the end of the Ice Ages was a time of global warming, when we came out of a time of very cold period into a time that was much warmer.
And we're quite concerned about that right now. The world is warming now. So, here you have these animals that survived, or didn't, a warming at high elevation. And one of the things we're concerned about now is, what happens to plants and animals that live at high elevation as the world warms? So, there's a pretty nice analogy for why these animals might be the bearers of some information that could be useful to help us understand our present situation.
TOM BEARDEN: Last week, a winter storm forced the Denver Museum scientists to shut down the site until spring. They will be back in May, when the ground has thawed and the search for ancient bones can continue.