In a frozen corner of Siberia, far north of where most humans care to live, there is a wildlife refuge where scientists are trying to rebuild an ancient ecosystem that could help slow global warming.
The plan depends on cold-resistant animals that graze and trample the tundra as their ancestors did thousands of years ago, a process that exposes the underlying soil to frigid air and protects it from a thaw that could release massive amounts of greenhouse gases into the atmosphere.
So far, "Pleistocene Park" has bison, oxen, moose, horses and reindeer — and the results are promising.
But it is missing the original ice-age icon: the woolly mammoth.
Yes, that woolly mammoth, the ancestral cousin of the elephant that walked the Earth thousands of years ago and now exists only in our imaginations — and in natural history museum dioramas.
Scientists want to bring it back.
It sounds outlandish, and, in some respects, it is. But a series of discoveries in recent years have made "de-extinction" of the mammoth and other lost species theoretically possible.
There are two teams trying in different ways to manufacture a mammoth — one by cloning, the other by DNA splicing — but they are united in a much larger effort to save endangered animals and bring back others that have disappeared. Both acknowledge that the goal is many years away, if it happens at all.
Watch Dateline's "On Assignment" on Sunday at 7 p.m. ET to see Harry Smith take viewers inside a cloning lab.
But why, of all things, the mammoth?
Getting its help to reclaim a lost ecosystem doesn't begin to explain.
The deeper answer lies in humankind's fascination with the earth's largest animals, and the mysterious circumstances under which many ancient giants disappeared.
"When we were children, we would go to the museum and see these large creatures that went extinct. One would be the dinosaur and the other would be ice age animals like the mammoth," said Insung Hwang, a biomedical engineer and project manager of a team that hopes to clone the mammoth. "That fascination carries over to when you become an adult. I had that fascination as a child."
Like many scientific endeavors, de-extinction follows people's hearts. Mammoths draw attention, and money. And it just so happens that massive mammoth graveyards, sealed for centuries under ice, are beginning to thaw as the Earth warms.
The discovery of well-preserved mammoths has sparked a rush of researchers who want to understand more about how the mammoths lived and died — and who want to find material that could help bring a mammoth, or something like it, to life.
Some of them, including Hwang, work for Sooam Biotech Research Foundation, a South Korean company best known for charging $100,000 to clone pet dogs. That process — taking a cell from a living or recently deceased animal, injecting its genetic material into a donor egg, then implanting the egg into a surrogate mother — has become relatively common.
But Sooam is trying to push the limits of the technology by harvesting intact DNA from mammoth remains. The team hopes to inject the DNA into an elephant egg and trigger the development of a mammoth embryo, which would then be implanted into an elephant's womb.
Myriad obstacles remain. The team has yet to find any viable mammoth DNA. And no one has figured out how to remove an egg from an elephant — or transplant an embryo into one.
"The general procedure, taking the nucleus of one cell and transferring into another, that's easy. You can do that in different labs all over the world. But all the other things that have to come together to make an animal is difficult," said Mark Westhusin, an expert in genetically engineered animals who teaches at Texas A&M University. "Getting the eggs, to begin with."
But Hwang pointed out that until a few years ago, it was considered unrealistic to find suitable mammoth remains at all.
"We're not close to finding viable material yet, but the samples are very well preserved, so that gives us hope that better samples can be found in the future," he said.
On the other side of the world, at Harvard Medical School, a team led by geneticist George Church is using newly developed genome-editing techniques to essentially build mammoth DNA and splice it into live elephant cells. But, again, if they pass that step, they would still need to create an embryo and put it in a surrogate mother.
But de-extinction has been proven possible with species that have vanished more recently. Thirteen years ago, a team of French and Spanish scientists managed to clone a bucardo, a type of goat that once lived in the Pyranees; the clone lived 10 minutes. Other projects have targeted the passenger pigeon, the gastric brooding frog and the heath hen — but they have not produced a clone.
On a separate but similar track, other teams are using similar techniques to try to save endangered species, such as the northern white rhinoceros.
But, one way or another, the discussion usually comes back to the mammoth.
That is why Beth Shapiro, a professor of ecology and evolutionary biology at the University of California at Santa Cruz, titled her recent book about de-extinction, "How to Clone a Mammoth." It's not that she necessarily agrees with the attempts to bring the animal back — there are a number of ethical considerations, including the welfare of the animals, the drawing of resources from other conservation efforts and questions over "playing God." But Shapiro says some of the applications, namely the carbon-trapping transformation of the Siberian tundra, are exciting.
"If by doing that we can reestablish these interactions that have been gone, and thereby save living species and living ecosystems from extinction, then I think this is a compelling reason to think about this technology," she said.