Fossils appear, blinking in the sun, uncovered by the annual winter draw-down of water in Percy Priest Lake in middle Tennessee. These fossils were creatures of shallow tropical seas, out of place now, stranded on a cold shore next to oaks and cedar trees.

Actinoceras. A mollusc that swam in the open water. Its shape is like an uncoiled Nautilus.

A honeycomb coral (Favosites?). The coral animals lived inside closely packed columns of calcium carbonate. Like modern corals, these were reef-building animals.

This stack is, I think, the remains of a stromatolite, a layered community of bacteria and bacteria-like cells.

The presence of these species in a decidedly untropical locale hints at the back-story. The waaaay-back-story. A pink bull’s eye sits in the middle of the geologic map of Tennessee. Unfortunately the rocks don’t conform to the geologists’ color codings. Cream or gray limestone is wan in comparison. These rocks date from the Ordovician, ~450 million years old, deposited when what is now Tennessee sat closer to the equator, a bathwater sea under a tropical sun. The good times couldn’t last, though. As more sediment arrived and the Earth’s drunken crust staggered northward, the Ordovician deposits got buried.

Geologic map from Tennessee Department of Environment and Conservation, Tennessee Geological Survey.

But burial was not forever. A cross-section reveals the peculiar history of this area. The pink, Ordovician rocks are older than those that ring them and were pushed to the surface by the upward poke of the Earth goddess into the crust, a gesture powered by the collision of continental plates. Because the Ordovician rocks are made from highly erodible limestone, the center of this dome wore away and now sits lower than its surroundings. A dome turned into a bowl. Hence the improved gas mileage as you drive into central Tennessee and the labored engine when you depart.

Image from Bruce Railsback, University of Georgia

Reefs are not the only remnants of life hidden under the lake’s waters. People forced by the US government onto the Trail of Tears (1838-1839) came through the old town of Jefferson. Then, in the 1960s, when the Army Corps of Engineers built the dam and filled the lake, they drowned roads, fields, and communities. As one former resident of old Jefferson recalled, the area “was the center of business for this end of the county. There wasn’t no Smyrna then.”

The Cherokees were forcibly bent to the will of the government. The Tennessee landowners in the path of the lake had no choice. History now repeats itself: today the Corps announced its intention to impose the desires of Andrew Jackson’s replacement on the Standing Rock Sioux Tribe, to forego environmental review, and waive its own policies. Soon, liquid fossils will flow through the pipeline. Expect water levels to rise.