As you watch this segment, think about how scientists drew conclusions about the consequences of climate change on some animals, such as the woolly mammoth.
About 10,000 years ago, the great herds of woolly mammoths suddenly vanished. To this day, scientists do not know for sure what happened. What we do know, is that the death of the woolly mammoth coincided with the end of the last ice age.
An ice age is part of what scientists believe is a cycle of warm and cold periods during Earth’s geological history. The ice age is the coldest part of the cycle, where temperatures are much colder than average and great sheets of ice called glaciers cover a large portion of Earth’s surface. Between the ice ages are periods of warming during which the glaciers melt.
Scientists think that in the last two million years, Earth has experienced at least four major ice ages. Most scientists believe these ice ages resulted from a combination of factors; one of the key reasons for this type of climate change involves a periodic change in Earth’s orbit around the Sun. Normally, Earth’s orbit is elliptical, however the orbit doesn’t remain constant and every one hundred-thousand years or so, Earth’s orbit brings it farther away from the Sun. Scientists believe that this additional distance from the Sun, is enough to contribute to an ice age.
Snow began to accumulate; over centuries, glaciers formed and moved from the poles and toward the equator.
“They don’t go fast; they typically, they go, you know, the length of a room a year. The fastest places can go a couple of miles in a year or something on that level, so they’re not fast but they’ve got great momentum; and anything gets in the way, they just keep going.” - Dr. Richard B. Alley (Professor of Geosciences – Penn State University)
And then, as Earth’s climate warmed up, the glaciers gradually melted. Today, scientists study ice cores for clues about climate change. Ice cores are long slender tubes drilled out of the deep thick ice that still covers the polar regions of Earth. Ice cores are made up of thin layers of snow; each layer represents one year.
“You could think of the ice core as being a sort of sack of annual weather summaries where each individual layer of snow contains a little bit of history about what the weather was like during that particular time of year.” – Prof. Kendrick Taylor (University of Nevada)
From ice cores, scientists have determined that the last ice age began about one hundred-thousand years ago. During that time, about thirty percent of Earth’s land area was covered by glaciers. On the North American continent, glaciers spread from modern-day Canada and then covered the northern United States, leaving a cover of ice more than three kilometers thick. In fact, the area where New York City stands today was almost completely buried in ice.
One of the few remnants of the last ice age is the remains of a woolly mammoth; this frozen block represents a record from the past. In an underground cavern in Siberia, scientists have set up a subterranean laboratory; piece-by-piece, they will thaw this block of mud and ice looking for clues about the woolly mammoth that once roamed the steps. Preliminary findings from the tusk reveal that the mammoth was in generally good health and faired well in its environment.
Next, Dr. Dick Mahl examines the mammoth’s teeth; it’s one way to determine how old the mammoth was when it died. Dr. Mahl concludes the mammoth was forty-seven years old. What might have contributed to its death? We know that toward the end of the woolly mammoth’s species, global climate began to warm; that would have affected the mammoth’s environment and their food supply. Scientists studying ice cores and other clues have found that as the ice sheets melted about ten-thousand years ago, the ocean rose some one-hundred meters, flooding the northern part of Siberia. The southern forests expanded northward, taking over the mammoth’s step; the mammoth’s grassy habitat was shrinking dramatically. Squeezed by forests on one side and water on the other, mammoths lost grazing area and they had no place to go.
Along with these changes, some scientists hypothesized that the warming climate could have led to massive mud-slides; the mud covered the mammoth after it died. The fact that this mammoth was found intact lent support to this hypothesis. The mud streams could have sealed out the oxygen that normally would have contributed to the decay of this mammoth. Then, with the on-set of winter, the temperatures plummeted again; snow and ice froze the ground and the buried carcass.
At this point, these ideas have not yet been proven, but many scientists think that climate change played a major role in the extinction of the woolly mammoth. As scientists continue their work in their icy lab, they may one day know for sure.
What major geologic event coincides with the extinction of the woolly mammoth?