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

Early History—Plains Evolution

The Earth formed with misty beginnings—most of its history is lumped into a section of time called the Precambrian. The Precambrian includes both the Archean and Proterozoic eons, which span from the formation of Earth about 4.6 billion years ago to the beginning of the Phanerozoic eon 541 million years ago. The first signs of life have been found as fossilized evidence from the Precambrian, before humans, dinosaurs and even most multicellular life existed. Earth’s atmosphere had not yet developed the oxygen-rich characteristics observed today, leaving these organisms to survive on anaerobic processes. The landmasses, though different than the modern continents, formed early and were molded by an episodic cycle throughout deep time.

That’s right, Pangea was not the only supercontinent—only the most recent. Evidence shows that six major supercontinents formed and disassembled long before Pangea, with other more minor assemblages occurring in between. The landmass we call North America was active in the continuing supercontinent cycle of Earth, though at first it was combined with other bits of land like Scotland and Greenland under a different name, Laurentia. As the continents crashed together and were pulled apart, the shape of Laurentia evolved into the familiar pattern of North America, including the ancient Great Plains region.

Things got exciting in the time after the Precambrian, starting with the Cambrian explosion. Often referenced for its trilobites (the ancient cockroaches of the sea), the Cambrian is famous for its detonation in the diversification of life. By the 500-million-year mark, the first marine vertebrates began to appear, and about 100 million years later, the first evidence of plants on land. The Phanerozoic era was the jump start of all life on Earth today, leaving behind some of the world’s most extensive and well-preserved paleontological deposits. Some of these, like the House Range in Utah and Mazon Creek in Illinois, are still treasure troves nestled into the vast expanses of the Great Plains.

Animals began the transition onto land around 360 million years ago; mammals did not appear until about 200 million years ago. Humans and their most recent ancestors have only been around for a fraction of that time: approximately 200,000 years, the tail end of the Cenozoic era. The earliest records suggest that Paleo-Indians may have arrived in the Great Plains region 15 thousand years ago, some even extending that number to 38,000 years ago. Carbon-dated remains from Wyoming provide evidence of humans at least as early as 8,500 BC. This range has led to the belief that humans may have shared time with now extinct megafauna—mammoths, giant sloths, and saber-toothed cats.

 

Featured photo courtesy of U.S. National Archives:

Fossils Are Seen Along Trail from Spanish Bottom, in the Maze, 05/1972

Find the photo here

 

See the following sources for more info:

http://plainshumanities.unl.edu/encyclopedia/doc/egp.na.001

http://palaeo.gly.bris.ac.uk/palaeofiles/lagerstatten/

http://www.ucmp.berkeley.edu/paleozoic/paleozoic.php

https://www.britannica.com/science/geologic-time

“Chapter 7 – The Supercontinent Cycle.” In Earth as an Evolving Planetary System, 201-35. 2016.

Mac Niocaill, Conall, and Mark A. Smethurst. “Palaeozoic Palaeogeography of Laurentia and Its Margins: A Reassessment of Palaeomagnetic Data.” Geophysical Journal International 116, no. 3 (1994): 715-25.

Wedel, Waldo R. “Prehistory and Environment in the Central Great Plains.” Transactions of the Kansas Academy of Science (1903-) 50, no. 1 (1947): 1-18.