Current Earth Science

Humans, the Short End of the Time Scale

The long-winded history of the Great Plains is recorded in the geological features we see today. The Precambrian shows itself in outcrops of the pink Town Mountain granite, the Packsaddle schist and Valley Springs gneiss. These rocks tell a story of massive chambers of boiling-hot magma being pushed to the surface to cool, and surrounding rocks being metamorphosed by intense heat and pressure. In the Paleozoic and later in the Cretaceous, ancient shallow seas covered the inner continent and produced carbon-rich rocks. Limestones, shales, and fossilized reefs are scattered throughout the Great Plains and nearby areas, evidence that the area was not always the ‘Great American Desert’. Decaying plant matter built up and compressed over time resulted in coveted coal deposits. When the waters retreated, the temperatures started going down, too.

Now, the Great Plains are dusted by a layer of younger sediments—sand and gravel and soil—eroded from the Rocky Mountains on the western border. These sediments help trap water underground in aquifers, supplying the region and its inhabitants. It is no surprise that pockets of water have been attracting all sorts of living beings for thousands of years, and early humans were no exception.

The common consensus among archaeologists is that humans began living on the Great Plains at least 11,000-11,500 years ago, based on carbon dating of various artifacts like bones, stone flakes and tools. This time overlaps with the last Ice Age, and the time of giant creatures like mammoths and saber-tooth cats (see Miocene and Mammoths). In 2005, a study took advantage of some broken mammoth bones that had been on display at the Denver Museum of Nature and Science for nearly 30 years. The bones appeared to have been broken by humans rather than by natural means, and were carbon dated at about 12,200 years old. Many scientists are drawn to the significance of discovering the oldest site with clear evidence of human habitation, and so research continues.

Humans have been fascinated by the challenges and opportunities offered by life on the Great Plains for a very long time, whether because of water and food resources, the hunt for gold and precious materials, agriculture, or an adventure. This curiosity is prominently realized in the mid-1800s, when Americans were surveying the Territories and some people thought that rain would follow the plow.

 

Featured photo courtesy of U.S. National Archive:

Hikers Terry Mcgaw and Glen Denny Enjoy a View of the Maze from the Top of a Ridge Separating Two Canyons. The Maze, a Wild and Rugged Region in the Heart of the Canyonlands, Has No Footpaths, and Hikers Enter by Means of Ropes Or Steps Cut in the Rocks,

 

See the following sources for more info:

http://geology.teacherfriendlyguide.org/index.php/rocks-sc/rocks-region4-sc

https://www.geosociety.org/documents/gsa/timescale/timescl.pdf

Denver Post Staff Writer. “Museum’s Mammoth Bones Exhibit New Life After Nearly 30 Years on Display, Fossils Found in Kansas Are Causing Scientists to Re-examine When Humans Arrived on the Great Plains. (DENVER AND WEST).” The Denver Post (Denver, CO), 2005.

Deep Time Snapshot

Miocene and Mammoths

Ever wonder what it’s like to meet a mammoth? It was possible—only a few tens of thousands of years ago on the Great Plains. We call this epoch in time the Pleistocene, spanning from 2.6 million to 11,700 years ago. In the span of geologic time, this is a miniscule segment in the history of Earth. The world was in the middle of an extreme ice age, and North America was almost in the same position we see it now. North America was also host to the largest ice sheet at the time: the Laurentide ice sheet, a forceful tool that carved and shaped the landscape as it spread and flowed.

The Pleistocene is famous for its fauna, including Smilodon, the saber-toothed cat that was 30 percent bigger than a modern African Lion. The Smilodon is one of the most extraordinary cats to have ever lived, thanks to its incredible musculature, jaw strength, and extra-long canine teeth. Paramylodon, the cousin of the South American Megatherium (which became the namesake of a research club in the 1870s—look out for this post!), was a giant ground sloth. Unlike today’s sloths, they walked on the ground on feet sporting claws 18 centimeters long and lived and reproduced in caves. Glyptodons were a weird animal that looked like a combination of an armadillo and a tortoise. It had a six-foot long tail and possibly an elephant-like trunk. Animators made use of these quirky creatures in their film, Ice Age.

These, among other animals of the Pleistocene, are not only found in the fossil record of the Great Plains, but also in the unusually diverse La Brea tar pits. Thousands of excellently preserved specimens have been found in the gooey oil-tar underneath Los Angeles, California. After a few animals got stuck, their plight attracted predators interested in an easy meal. Some of the predators got stuck themselves, bringing in even more critters, creating a cycle. As a result, the tar pits have provided a snapshot of life in the Pleistocene, life that could be seen not just in (not so) sunny California, but across the continent.

Even more well-known are mammoths—some of the largest mammals ever walking the Earth. In the cold, harsh environment of the ice age, mammoths found refuge in a stretch of grasslands near the Sierra Nevada Mountains. Columbian mammoth remains have been found near ancient equine, bison, and sheep remains in the Upper Missouri Basin, the Rocky Mountains, the Yellowstone Basin and more. Basically, if there was vegetation available for eating, mammoths lived there. Some studies have even found mammoth limb bones showing evidence of human modification—giving light to the claim that early humans shared a world with these giant animals.

 

Featured image courtesy of U.S. National Archive:

Mt. Moran and Jackson Lake from Signal Hill, Grand "Teton National Park," Wyoming.

 

See the following sources for more info:

https://tarpits.org/la-brea-tar-pits/timeline

https://www.geosociety.org/documents/gsa/timescale/timescl.pdf

 

Flowers, Mark., Mags. Lightbody, Dominic. Frisby, and British Broadcasting Corporation. Ice Age Giants. Land of the Sabre-tooth. VAST: Academic Video Online. London, England: British Broadcasting Corporation (BBC), 2013.

Hill, Christopher L. “Stratigraphic and Geochronologic Contexts of Mammoth (Mammuthus) and Other Pleistocene Fauna, Upper Missouri Basin (northern Great Plains and Rocky Mountains), U.S.A.” Quaternary International 142 143 (2006): 87.

Holen, Steven R. “Taphonomy of Two Last Glacial Maximum Mammoth Sites in the Central Great Plains of North America: A Preliminary Report on La Sena and Lovewell.” Quaternary International 142 143 (2006): 30.