Scientists just uncovered three ancient worlds frozen beneath Illinois for 300 million years

More than 300 million years ago, during the Carboniferous Period, much of northern Illinois outside Chicago — including what is now the Mazon Creek (“muh-ZAHN”) fossil site — was alive with ancient creatures thriving in lush, tropical swamps, river deltas and shallow seas.

Now, researchers at the University of Missouri’s College of Arts and Science are collaborating with geologist Gordon Baird to reanalyze his massive fossil collection from Mazon Creek — currently housed at the Field Museum in Chicago — which includes 300,000 siderite concretions from around 350 different localities.