Climatic and environmental conditions in prehistoric Oklahoma differed greatly from those of our own time. The physical landscape and climate that we know today have endured for around three thousand years without significant change. Some scientists even debate the question of whether, at the end of the twentieth century, the environment remained in an ice-free period of the last glaciation or had entered a new climatic era engendered by human actions (e.g., global warming). The environmental record over the past thirty thousand years, however, documents numerous events reflecting both major climatic changes as well as lesser "climatic fluctuations." Both climatic change and fluctuation brought changes to the physical landscape and in the plant and animal communities that prehistoric people relied upon as critical resources. For example, with drier, warmer conditions, grasslands and associated animal communities shifted to the east. With the return of more moist climate, woodlands and associated animals shifted their distributions westward. These shifts of east-west plant and animal communities pulsed repeatedly through time, undoubtedly influencing the movement and economic activities of prehistoric groups.
Between some 30,000 and 15,000 years ago glacial conditions faced humans who may have inhabited the region that is now called Oklahoma. The climate at that time was significantly cooler and moister than it is today. Forests of spruce and pine interspersed with grasslands covered the northern portions of the region, oak-hickory forests were found in the southeast, and grasslands occurred in the southwest.
Pleistocene megafauna such as mammoth, giant ground sloth, horse, camel, saber-toothed tiger, and numerous other animals common to the Wisconsin glacial era dominated the animal community. Oklahoma was hardly a barren, arctic-like setting. Evidence indicates that many modern species also inhabited the area. In fact, data shows that alligators roamed northwestern Oklahoma some 28,000 to 32,000 years ago. Obviously, then, interglacial conditions were less severe, permitting the presence of such species when the climate stabilized.
Conditions during the late glacial era would have provided for the presence of rich plant and animal communities for exploitation by the early Native inhabitants. Beginning around 15,000 years ago the glacial climate began to moderate, becoming warmer and drier. During this time many of the large game animals that had been present during the glacial eras now died out. By the end of the period (circa 10,000 years ago), the giant bison (Bison antiquus) was the only remaining example of the many Ice Age megafauna once found here.
Between 7,000 and 4,000 years ago Oklahoma experienced a prolonged period of drought yet unsurpassed in severity and duration. Because higher temperatures are typically present in the spring and summer months, this period is termed the Altithermal. Grasslands extended over as much as two-thirds of the present state, with only the easternmost part of the region retaining its woodland character. In some areas of southwestern and western Oklahoma, conditions might have resembled those of present New Mexico. Antelope, bison, jackrabbit, and other animals inhabiting much of Oklahoma were species better adapted to arid environments. Arid conditions presented formidable challenges to small groups of hunters and gatherers. Many of these people may have retreated to the eastern margins where more moderate conditions prevailed. However, ample evidence demonstrates that groups adapted to these harsh conditions throughout the region.
Hot, dry conditions slowly began to improve, and by roughly 3,000 years ago the climate resembled that of today. Due to increased moisture and somewhat cooler temperatures woodlands advanced westward, and grasslands retreated. Animal communities also began express better balance between plains and woodland habitats. Human populations undoubtedly also expanded across Oklahoma, reoccupying areas that perhaps had been only sporadically traversed during the Altithermal. From around 1,500 years ago until approximately 900 to 1,000 years ago, fluctuations in climatic conditions brought a period of increased rainfall. Whether temperatures were cooler or warmer than today is not well documented. However, increased precipitation spurred expansion of woodland plant and animal communities westward, at the expense of plains-adapted communities. During this period is found the first evidence for domestication of plant species in the region (although not specifically in Oklahoma), a development perhaps made feasible by increased soil moisture.
This period of increased precipitation was soon followed by one of greater aridity, beginning around 800 years ago. Farming by prehistoric societies actually intensified until around 500 years ago, suggesting that reduction in rainfall may have been a gradual phenomenon. An apparent resurgence in plant and animal communities expressed greater plains adaptation. Arid conditions culminated during the period between roughly 600 and 400 years ago, coinciding with a time of significantly cooler temperatures sometimes referred to as the "Little Ice Age." These climatic changes proved disastrous to farming peoples in Oklahoma and elsewhere in the region, with many groups abandoning agricultural practices in favor of nomadic bison hunting. Europeans encountered this final climatic scene in their journeys to the Southwest and the southern Great Plains in the mid-sixteenth and early seventeenth centuries.
Thomas D. Dillehay, The Settlement of the Americas (New York: Basic Books, 2000).
Brian M. Fagan, Ancient North America: The Archaeology of a Continent (London, England: Thames and Hudson, 1995).
Claudette Marie Gilbert and Robert L. Brooks, From Mounds to Mammoths: A Field Guide to Oklahoma Prehistory (2d ed.; Norman: University of Oklahoma Press, 2000).
Waldo Wedel, Prehistoric Man on the Great Plains (Norman: University of Oklahoma Press, 1961).
Don G. Wyckoff and Robert L. Brooks, Oklahoma Archeology: A 1981 Perspective, Archeological Resource Survey Report No. 16 (Norman: Oklahoma Archeological Survey, 1981).
The following (as per The Chicago Manual of Style, 17th edition) is the preferred citation for articles:
Robert L. Brooks, “Paleoenvironment,” The Encyclopedia of Oklahoma History and Culture, https://www.okhistory.org/publications/enc/entry.php?entry=PA007.
© Oklahoma Historical Society.