Friday, January 23, 2015

Precambrian Ohio

The Precambrian era was the earth's earliest stages and lasted from about 4.5 billion years ago, to approximately 570 million years ago. The earth had just became solid and therefore most rocks from this period formed during the late Precambrian era. The first rocks formed in Ohio were granite and rhyolite. The granite rocks were formed from the magma and pressure inside the earth, whereas the rhyolite rocks formed from all of the volcanic activity going on in Ohio at the time. These rocks formed a 7 mile thick layer with the rhyolite on top of the granite, (source:
This layer of rock is referred to as the "basement" since all other rocks formed since this time period lay on top of it. Eventually this layer of rock split and caused rifts to be filled with lava and sediment, causing new rocks to form. Down below is a Precambrian map of the continents and tectonic structure of the world.
Late Precambrian continental structure. (From

Believe it or not, Ohio used to be on the the eastern shore of our continent, until another continent collided with ours and caused mountains to form in modern day Ohio. Now the granite and rhyolite rocks are crystalline, extremely hard and resistant to weathering, ( from but the mountains that formed eventually eroded which led to the sedimentary rocks of later periods.
When the two continents collided, they created the Grenville Front Tectonic Zone, which still exists today as show on the map below.
Map of the Grenville Tectonic Front Zone today.

 The end of the Precambrian era was marked by seas flooding Ohio.

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