It’s Getting Hot In Here
by Kristie Erickson, Special Project Curator

Global climate change is not only a hot issue now, it was a major concern 10,000 years ago.

The last ice age was at its peak 22,000 years ago, when glaciers in North America could be up to three kilometers thick, rising to the altitude of today’s rain clouds. They were so massive their weight deformed the earth’s crust, which is still rebounding today. So much water was frozen that ocean levels were about 135 meters below today’s level, connecting Asia to the Americas, and Australia to New Zealand. These glaciers were so large they affected climate all over the world and even had their own weather systems. When they began to disappear, it is only logical it affected animal life.

Many believe human hunting led to the extinction of ice age megafauna, a theory known as the Overkill Hypothesis. However, hunter-gatherer groups usually have a population density of only one person per ten square miles, meaning only a few thousand people at most would have been able to live in a space the size of Indiana. Though they did eat their share of mammals, they also ate an abundance of vegetation – basically anything edible they came across was eaten. Though human hunting certainly put additional pressure upon these animals, additional factors also contributed to their decline. Most easily seen in the paleontological and geological records is the effect of climate change.

After the glacial maximum the earth began to warm and the glaciers to melt. This warming could have been caused by several factors, including increased carbon dioxide and the tilt of the earth’s axis, but the changing climate had a profound effect on the flora and fauna of the Americas. As it emerged from the cover of ice, the climate of Michiana first became tundra and then taiga, similar to today’s Siberia, cool and covered in large expanses of coniferous forest. Mammoths ate the grasses of the steppes and generally lived farther west, and most fossils found in our area are of mastodons, which are browsers. As the earth continued to warm, this taiga began to disappear, as did the steppes, putting even more pressure on the populations.
Disease also impacted ice age megafauna, only made worse by the now warmer and wetter climate. Scientists Bruce Rothschild and Richard Laub’s analysis of mastodon skeletons from the end of the last ice age has shown evidence of tuberculosis in almost half of the population. In its later stages, tuberculosis erodes the bones of phalanges, leaving evidence that can be identified by scientists. Tuberculosis is visible in the bones of only 7-10% of individuals affected today, indicating an epidemic that may have infected almost all mastodons, weakening their population significantly. Tuberculosis also affects bovids, such as bison, sheep, and goats, and could even have spread to the human population. As their environment disappeared, rampant disease only made their situation worse, and the loss of these species would have been devastating to the entire ecosystem.

As if all these weren’t enough, an old theory on ice age extinction is gaining new credibility. Recent analysis of a black mat, found in sites all over the North American continent and dating to about 10,900 years ago, have revealed nanodiamonds that can only be formed during the heat and pressures of an extraterrestrial impact. Scientists believe a comet or large meteorite may have exploded over, or even impacted upon, the Laurentide ice sheet near Lake Michigan. This would have been somewhat similar to the Tunguska event of 1908, where an object exploded over Siberia and flattened 2,000 square kilometers of taiga, but on a much larger scale. Called the Younger Dryas Impact, a release of energy this large would not only have melted the Laurentide ice sheet, it would have set the entire continent ablaze, destroying much of the animal life and depositing burned debris into the geological record, resulting in the black color of the mat. A disaster of this size may have been the final blow to the megafauna of the ice age.

Curiously enough, the Younger Dryas Impact may have also intensely affected the course of human history. The Younger Dryas is a short period of rapid cooling in Europe and Asia starting about 11,000 years ago, when an abrupt influx of fresh water from North America emptied into the North Atlantic and interrupted the ocean currents that bring heat to Europe. If there was indeed such an impact, it is likely that sudden influx of meltwater was the catalyst for this interruption. Archaeologists believe this sudden cold spell may have incited the people of the Levant to begin to purposefully cultivate plants, in order to have a more reliable food source – the beginning of agriculture.

While climate change and giant meteors are devastating to people, plants, and animals, it is only under pressures like this that we evolve. The invention of agriculture is the foundation of civilization as we know it, leading to everything we see in the world around us, from books and electricity to warfare and Paris Hilton. So next time you’re perusing the giant mammals of TUSKS! and pondering life during the ice age, just think – if it weren’t for them we wouldn’t have America’s Next Top Model. Decide for yourself whether we’re better off.