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| Volunteers at the Cedar Creek Mastodon Site in Morrow County, Ohio., on October 25, 2014. The exposed white plastic corrugated drainage pipe in the foreground triggered the excavation when the digging for it exposed two mastodon teeth in September 2013. The soybean farmer installed the pipe to drain water flowing from upland (background) toward Cedar Creek Bog, which is not too far from this pipe, but not shown in photo. In October, a trench was cut nearby to the bog to compare soil layers of the bog, excavation pits, and surrounding land. (Photo by Don Comis) |
At the time the Cedar Creek mastodon died, it was not far from a bog surrounding a quiet shallow lake, with abundant growth of algae and other plants, as well as freshwater mollusks, like ram’s horns snails. This lake was once the deepest part of a large glacial lake that covered the Cedar Fork Valley in Morrow County, Ohio, about 15,000 years ago, when the last of the glaciers that had covered two-thirds of Ohio melted. The glaciers are what carved out the U-shaped Cedar Fork Valley.
The large lake was created by the melting, during a warming period between 20,000 and 15,000 years ago. The water was dammed in by glacial walls. When those walls melted, the lake drained, leaving only the deepest remnant, which began to fill with mud from decayed peat. As the climate warmed much more abruptly, the mud layer became a marl layer, lime-rich mud, within 500 years. Around the time of the Cedar Creek mastodon, another cooling period began, abruptly changing the mud back to peat as water levels dropped further.
The lake that the mastodon and early man walked near was filled with plant and animal life. The coarse gravels at the base of the mastodon site were the bed of a pre-glacial stream that fed the lake.
Entombing Bones and Artifacts
The mud with broken pieces of rocks above the gravel likely came from debris flows as water flowed from the surrounding higher elevations, “entombing the bones and artifacts under a slurry of muddy debris,” according to a preliminary report by Gregory Wiles and his College of Wooster (Ohio) Climate Change class.
Wiles sent the report recently to excavation leader Nigel Brush, associate professor of geology at Ohio’s Ashland University. The report also says that the high calcium carbonate content of the mud helped preserve the mastodon bones and associated man-made objects.
The report presents results of analyses of soil cores taken in and around the bog and nearby mastodon site, soil mapping, observations of soil layers in a trench dug in October, connecting the bog and the mastodon site, as well as radiocarbon dating. Analyzing these cores reveals the periodic warming and cooling of the planet over the past 15,000 years, caused by changes in the earth’s movements as it rotates and revolves around the sun, changes in ocean circulation, and changes in greenhouse gas levels.
Last September, Wiles--with Tom Lowell and his graduate student Stephanie Allard, at the University of Cincinnati, and University of Illinois student Jacklyn Rodriguez--collected the sediment cores from the bog. Earlier, in August, the College of Wooster students had used soil probes to map soil depths down to 20 feet in the bog.
Two Million Years of Climate Change
The report’s introduction says that, “The Earth has spent the last 2 million years in a state of constant flux, moving between 20 periods of intense cold and glacier cover and periods of warming and glacial melt.”
Wiles and his students also participate in a tree ring project that seeks answers to the question of whether the widespread deforestation and the draining of wetlands by the early Ohio settlers could have caused a major drought in the early 1800’s, revealed by studying tree growth rings in old trees throughout Ohio. Their blog says: “This question is relevant to the ever-present striving of climate scientists to investigate the relative roles of natural climate variability and anthropogenic [caused by man] change.”
Many of Ohio’s trees date back to the 1600s, including some at Kenyon College in Gambier, Ohio, near my Apple Valley home. The group studies old trees, including places in Wayne County, such as the Johnson Woods State Nature Preserve as well as the Secrest Arboretum, and on the campus of the College of Wooster.
The group made its last visit to the mastodon site on Nov. 13, also reported on the group’s blog , which includes more information as well as photos and a "Tree Detective" video on the tree ring project. Project participants also document the ages of barns as well as changes in climate by examining the tree rings from core samples taken from barn beams and comparing them to old living trees around the barn and throughout Ohio.
