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150,000 to 100,000 years Before Present
Climate Change in the Prehistoric Era
Dig site at Ziegler Reservoir. (c) Denver Museum of Nature and Science
When many people picture the Rocky Mountains, they picture pine-covered ridges or elk herds grazing winter meadows. Add in some growing towns, ranches, or the snaking trails of ski slopes, and you have a fairly accurate mental image of certain parts of the modern Roaring Fork Valley. But the valley didn't always look this way. How did the changes occur that took us from being the stomping grounds of mastodons to the ecological communities of today? Hidden evidence, ranging from pollen in local lake beds to ice cores taken from the arctic poles, can help to reconstruct what this region looked like in ancient times and provide clues as to the global trends that shaped it.
Mastodons, Sloths, and the Ziegler Reservoir
Long before humans began effecting changes of our own on the environment, the Earth's landscapes had already experienced dramatic shifts in climate, vegetation, and even geography. The fossil dig at Ziegler Reservoir, near Snowmass Village, Colorado has proven to be a prolific site for unearthing clues as to what happened in this region from 150,000 to 50,000 years ago.
The fact that both mastodons and mammoths were found at Ziegler Reservoir in Snowmass, Colorado, indicates that this area went through significant ecological shifts. What caused those changes to occur? Climate and ecology are related. Although the rate at which changes occur on the ground can be difficult to estimate, ice and ocean sediment cores can be used to reconstruct atmospheric climates of the ancient past and how they changed over time. The above graph uses data generated by the National Oceanic and Atmospheric Administration (NOAA) using ice cores from the EPICA site in Antarctica to show trends in ancient climates. The blue line represents departure from the average global temperature of the last 1,000 years. It begins at 550,000 years before 1950 on the left and continues through 1950 on the right.
Over the course of Earth's existence, the planet has been subject to periods of cooling and warming that drastically alter the appearance of the land and what can live there. It is important to note, however, that these changes took place over thousands of years. Glacial and interglacial cycles are determined by a combination of factors: the Mihlankovitch Cycle, CO2 concentrations, and water vapor patterns and presence. In the past century, one of these components--CO2 concentration--has been radically altered by human activities, so much so that it may lead to a departure from the previous glacial cycles of this planet. In the time period shown in the graph above, it can be seen that a change of roughly 2 degrees Celsius occurred over a time frame of several thousand years. Today, with human alterations of the atmosphere, the world is on track to experience that same 2 degree amount of change in a matter of a just a century.
Throughout time, who and what can survive in the Roaring Fork Valley has been heavily influenced by changes in the broader climate of Earth. Colorado has experienced great extremes from its current moderate conditions. Millions of years ago, this region was covered by a shallow sea. Even within more recent history, after the formation of the Rocky Mountains, the area swung between dramatically different climates. Within the last 500,000 years the area experienced snow-covered ices ages followed by warmer, milder periods when lakes and meadows formed.
Brain BugConsidering changes that occurred in previous history, what do you think the Roaring Fork Valley will look like 1,000, 10,000, or 100,000 years from now? What conditions would be necessary for these changes to occur, and how would they come about?
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