The Ancient World
was located much closer to the equator. A shallow
sea covered most of the southeastern United States,
and its warm water supported a dense population of
tiny organisms whose shells were made of calcium
carbonate (CaCO3). As these creatures died, their
shells accumulated by the billions on the sea fl oor.
In addition, calcium carbonate can precipitate from
the water itself. The build-up of material continued
for 70 million years accumulating seven hundred
feet of limestone and shale followed by sixty feet of
sandstone that was deposited over much of the area
by a large river system fl owing into the sea from the
north.
About 280 million years ago the sea level started to
fall exposing the layers of limestone and sandstone.
Additional tectonic forces caused the earth’s crust
to slowly rise causing cracks to form in and between
the limestone and sandstone formations. As the uplift
continued, rivers developed which over millions
of years have created the sandstone-capped plateau
above the Green River and the low, almost fl at limestone
plain which extends southeast of I-65.
