The Geologic Time Scale

Our study of the land cover and land-use history of the Colorado Plateau is of necessity limited to the Holocene, the last 11,000 years of the Earth's history since the end of the last major glacial epoch, or ice age. During the Holocene there have been smaller scale climate shifts—notably the "Little Ice Age" between about 1450 and 1850 A.D.—but in general the Holocene has been a relatively warm period between glacial advances.

Another name for the Holocene that is sometimes used is the Anthropogene, the "Age of Man." This is somewhat misleading since humans of our own subspecies, Homo sapiens sapiens, had evolved and dispersed all over the world well before the start of the Holocene. Yet the Holocene has witnessed all of humanity's recorded history and the rise and fall of all its civilizations.

Humanity has greatly influenced the Holocene environment. While all organisms influence their environments to some degree, few have ever changed the globe as much, or as fast, as our species. Reputable scientists agree that human activity is at least partly responsible for "global warming," the current increase in mean global temperatures. Habitat destruction, pollution, and other human-caused factors are clearly implicated in an ongoing mass extinction of plant and animal species. According to some projections, 20% of all plant and animal species on earth will be extinct within the next 25 years.

Yet the Holocene has also seen an explosion of human knowledge and technology, which can be used—and is being used—to understand the changes that we see, to predict their effects, and perhaps to stop or ameliorate the damage to our planet. Perhaps the greatest work of the 21st century will be the undoing of some of the greatest work of the 20th century.

Packrat Midden Research in Grand Canyon. On the Colorado Plateau the ice age (Pleistocene) vegetation of the Grand Canyon has been determined through the analysis of plant fossils preserved in caves and fossil packrat middens.  Large changes occurred as the most recent ice age ended and the Holocene era began.

Late Holocene Environmental Change in the Upper Gunnison Basin, Colorado. The Upper Gunnison Basin is a high elevation (3100 to 3600 m) region on the edge of the Colorado Plateau in southwestern Colorado. Its unusual ecological characteristics include an absence of plant and animal taxa that should occur here. Fossil and archaeological evidence indicates that many of the missing species existed in the Basin during the late Pleistocene to middle Holocene.