Geologic history of Northeastern Illinois and Southeastern Wisconsin
The image was gathered by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite at 1:30 p.m. Central Daylight Time (18:30 UTC) on August 28. Open water appears blue or nearly black. The pale blue and green swirls near the coasts are likely caused by algae or phytoplankton blooms, or by calcium carbonate (chalk) from the lake floor. The sweltering summer temperatures have produced an unprecedented bloom of toxic blue-green algae in western Lake Erie, according to the Cleveland Plain Dealer.acquired August 28, 2010 Caption by Mike Carlowicz.
The earliest history of the upper midwest is recorded by ancient rocks of Precambrian age. In places over two billion years old, and commonly altered from their original appearance, these rocks represent the deposits of ancient seas, volcanos, and underground bodies of liquid material called magma. They do not contain fossils, and they form the basement on which fossiliferous strata of the Paleozoic Era were deposited.
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