In 2010, a woolly mammoth carcass was discovered in Siberia near the coast of the Laptev Sea. Nicknamed "Yuka," the long-extinct beast died around 28,000 years ago. Yet her body was astonishingly well-preserved, complete with patches of reddened fur, a brain that was largely intact and nucleus-like cell structures.
How did her corpse last this long without rotting away? The short answer is, Yuka was frozen — but not inside some glacier or iceberg. After death, Yuka became encased in a layer of what's known as permafrost.
As we know, water freezes at 32 degrees Fahrenheit (0 degrees Celsius). Permafrost is any ground material — such as soil, sediment and rock — that remains at or below freezing temperatures for at least two consecutive years. About 25 percent of all the land area in the Northern Hemisphere is known to contain permafrost.
It was American paleontologist Siemon W. Muller who originally coined the term "permafrost," a portmanteaux of the words "permanent" and "frost." Despite that name, permafrost doesn't last forever. Thanks to climate change, it's been thawing in large quantities. This has serious ramifications for both the environment and the economy.
Generally speaking, permafrost tends to occur in places where the average air temperature is 0° Celsius (32° degrees Fahrenheit) or lower every year. According to the National Snow and Ice Data Center, most of the Northern Hemisphere's permafrost sits between the high latitudes of 60 and 68 degrees north. Siberia, Canada, Alaska and parts of Scandinavia are loaded with this frigid turf.
Further south, permafrost tends to be found in high-elevation areas — like the Tibetan Plateau, the Hindu-Kush Mountain Range and the Swiss Alps. Permafrost isn't as widespread below the equator, but it does underlie parts of New Zealand, the Andes Mountains and Antarctica.
Just as its locations vary, so does its composition; it's not uniform. Some section are ice-free, while others are made up of more than 30 percent ice. Likewise, the depth, age and extent of permafrost can vary widely.
Oftentimes, permafrost sits beneath an "active layer" of ground, which thaws and re-freezes seasonally. The permafrost itself can measure anywhere from less than 3.2 feet (1 meter) thick to more than 4,921 feet (1,500 meters) thick.
And it can get patchy. Northern Alaska occupies a "continuous permafrost zone." That means permafrost underlies more than 90 percent of the local terrain. But at lower latitudes it's a different story. Pretty much everything south of the Brooks Mountain Range sits in a "discontinuous permafrost zone." Here, permafrost resides under a smaller percentage of the land's surface.
Snow, Trees and Water
Counterintuitive as it sounds, snow is a really good insulator. So when thick blankets of it stick around all year long, they might keep the ground too warm for permafrost. Likewise, in spots where permafrost already exists, insulating layers of surface-level snow are liable to heat it up.
But while snow's an impediment, peat is a boon. Widespread in and around the southern Arctic, peat is a kind of substrate that's made of partially decayed organic matter (e.g. mosses and swamp plants). By and large, the ground beneath it is kept cool, shielded from solar heat. Thus, peat safeguards permafrost.
Evergreen forests lend a helping hand, too. With their thickly needled branches, pine trees limit the amount of sunlight and snow that hits the ground's surface. In the process, the evergreens help keep permafrost from thawing. So it's no wonder that permafrost is common below the clustered pines in high-elevation and high-altitude areas.
The arrangement is mutually beneficial. Since liquid water can't seep through hard permafrost, it acts like a drainage barrier. Unfrozen water that's absorbed into the active layer gets trapped there. Barred from traveling deeper into the earth, this water sustains some of the plants that live at the surface.
The Deep Past and Uncertain Future
Sometimes, permafrost forms in concert with the ground itself. When this happens, the temperature of newly deposited soils, sediments and rocks hits 32 degrees Fahrenheit (0 degrees Celsius) very quickly. On the other hand, permafrost can also develop when an existing sample of un-frozen ground is chilled from the surface level downward.
At minimum, the permafrost in Prudhoe Bay, Alaska is thought to be 500,000 years of age. And some of the permafrost beneath Canada's Yukon Territory could be more than 700,000 years old.
Inside the latter, scientists found an ancient horse leg — complete with DNA samples. Permafrost can keep all kinds of organic matter preserved over long periods of time. In 2012, Russian scientists actually regenerated live tundra plants from ice age fruits that had been encased in permafrost for about 30,000 years.
Unfortunately, as permafrost thaws, that trapped organic material decomposes, releasing carbon and methane into the atmosphere. Those gasses exacerbate climate change. And the bad news is, according to a 2019 study published in Nature Communications, various permafrost deposits around the world have warmed up by about 39.7 to 32.8 degrees Fahrenheit (0.39 to 0.1 degrees Celsius) between the years 2007 and 2016.
Right now, approximately 1.7 billion tons (1.6 billion metric tons) of carbon is trapped in permafrost. Scientists don't know how much of this will be released into the atmosphere if current thawing trends continue — or how quickly it'll escape. But some projections are not encouraging.
To make matters worse, when permafrost thaws, it can destabilize the landscape. In the city of Norilsk, Russia alone, more than 100 residential buildings have been damaged because the once-solid permafrost beneath them is softening. The warming of permafrost has also triggered landslides, drained lakes and torn roads apart.
NOW THAT'S Amazing
Remember the wooly mammoth Yuka found in Siberian permafrost in 2010? She was so well preserved that in early 2019, scientists were actually able to extract 88 nucleus-like structures from her cells and attempt to "coax" them back to life. The team injected the nuclei into mouse ovarian cells, and while the cells never fully divided, they did complete the process called "spindle assembly," which is the step confirming chromosomes attach to spindle structures before the parent cell breaks into two daughter cells. Pretty cool stuff!
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