The Great Unconformity - Welcome to the surface of the Earth, approx. 550 million years ago. The first layer of rock, at ground level here, is called the Vishnu Schist. It consists of several complex sets of sedimentary and volcanic that were laid down 1.8 billion years ago, but were buried and metamorphized into schist and gneiss about 400 million years later.
By 550 million years ago, the Vishnu Schist was exposed as a flat, rocky plain that was inundated by the sea. The upper, layered rock is the Tapeats Sandstone and is made of beach sand. The Tapeats begins the sequential series of deposition that ends at the top of "The Grand Staircase" of the American Southwest.
What happened in the 1.2 billion years of Earth's history between the deposition of this basement rock layer and its final exposure is still unknown to science. One thing that is known is that life came to Earth. There is no evidence of fossils or trace of bacterial colonies in the PreCambrian schist and gneiss, but the Tapeats Sandstone and the layers above it show the rich tapestry of evolution through a fairly continuous fossil record.
Grand Canyon GigaView is a new school virtual tour of the Grand Canyon created with a collection of spherical GigaPan images taken on a private rafting trip in April 2010 and geolocated in Google Earth, Bing Maps, and 360Cities. Explore the journey http://grandcanyongigaview.tumblr.com/
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