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:

“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.

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