Illustration by Barry Roal Carlsen, provided by University of Wisconsin—Madison.

Did people kill off Pleistocene megafauna in North America, or were those species done in by climate shifts? Or…?

This question is still not answered unambiguously.

However, research by Jacquelyn Gill of the University of Wisconsin—Madison shows that neither scenarios is probable based on fossil pollen, charcoal and dung fungus spores that date to just after the ice retreated. Neither the mass extinction model, based on heavy hunting, nor simple climate and thus habitat change matches the data she and colleagues Stephen T. Jackson (University of Wyoming), Katherine B. Lininger (University of Wisconsin—Madison), and Guy S. Robinson (Fordham University) have marshalled.

According to Terry Devitt’s story (19 November 2009) on the University of Wisconsin—Madison website:

The decline of North America’s signature ice age mammals was a gradual process, the Wisconsin researchers explain, taking about 1,000 years. The decline in the huge numbers of ice age animals is preserved in the fossil record when the fungal spores disappear from the record altogether: “About 13.8 thousand years ago, the number of spores drops dramatically. They’re barely in the record anymore,” Gill explains.

Devitt continues:

While both the extinction of North America’s ice age megafauna and the sweeping change to the landscape are well-documented phenomena, there was, until now, no detailed chronology of the events that remade the continent’s biological communities beginning about 14.8 thousand years ago. Establishing that the disappearance of mammoths, giant beavers, ground sloths and other large animals preceded the massive change in plant communities, promises scientists critical new insight into the dynamics of extinction and its pervasive influence on a given landscape.

Archaeologists are often confronted with this situation: how do we get data on human behavior or the human situation, when we don’t have it directly from the archaeological record of human occupations? This research by Gill and her colleagues shows one solution developed to help understand the ecological situation in interior North America early in human occupation of the continent.

Stand by for more data….

Scientists studying ice cores from Antarctica and Greenland conclude that the Earth’s climate changed rapidly about 14,700 years ago. They studied the oxygen isotopes in air bubbles trapped in the ice. About 14,700 years ago, they found changes in the air that came from increases in vegetation levels. These increases happened over about 200 years, which is quite rapidly.

Credit: Zina Deretsky, National Science Foundation

The press release notes:

The ratio of ¹⁸O to ¹⁶O found in an ice core has shown the history of abrupt climate change on Earth. For example, dry spells around 14,700 years ago resulted in the planet being quite arid north of the equator. Monsoons that followed, caused the proliferation of vegetation north of the equator 14,500 years ago.

Combine this with information from the National Science Foundation’s 2009 report “Solving the Puzzle: Researching the Impacts of Climate Change Around the World.” On page 62, the report says:

Earth’s landmasses support critical ecosystems, host Earth’s freshwater environments, and sustain almost all human agricultural activities. Land separates freshwater from the sea, stores nutrients essential for terrestrial and aquatic life, and holds a fossil record of Earth’s climatic past. As the planet warms, the conditions favorable to many plant and animal species are expected to shift toward the poles. Individual species will differ in their ability to make the same shifts. The resulting altered species distributions will likely cause significant disruptions to established ecosystems, as habitats adjust to new species populations.
Land use is inextricably linked to the carbon cycle. Changing land-use patterns, such as clearing forest to create agricultural plots, change the dynamics of the carbon cycle. Livestock such as cattle contribute a net surplus of carbon to the atmosphere in the form of methane, a powerful greenhouse gas.

Past climate change patterns are not predictors of the rate of change we may be experiencing today.

Undisturbed archaeological remains buried in the soil contain all sorts of chemical clues invisible to the human eye. The oxygen isotopes in the air bubbles in the ice are a similar invisible clue. Visible archaeological remains can also reveal clues as to the climate in the past. What invisible chemical information about the climate of the past do you think may be contained in archaeological sediments, artifacts, and features?

Read the full press release on the Science article by clicking here.

Click here to go to the National Science Foundation’s website, where you can download their 2009 report “Solving the Puzzle: Researching the Impacts of Climate Change Around the World.”