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 1.8-1.7 billion-year-old metamorphic rocks in the Black Mountains above Badwater. Photo by Ray Nordeen, NPS. |
Dawn's Early Light: Middle Precambrian time
The Earth is 4.55 billion years old, but most rocks dating from the earlier half of that long history lie hidden beneath thick accumulations of younger rocks. In the Death Valley region the crust has been stretched, torn, and has collapsed into a system of enormous basins. Faults along the mountain range fronts have lifted deeply buried rocks up to the surface, revealing Death Valley's ancient basement rocks.
The oldest rocks exposed in Death Valley are about 1.8 billion years, almost half the age of the Earth. These venerable rocks are the remnants of an ancient volcanic mountain belt with its flanking deposits of mud and sand.
At about 1.8-1.7 billion years ago, these volcanic and sedimentary rocks were severely metamorphosed--altered, recrystallized, and partially remelted by the Earth's internal heat and by the load of overlying younger rocks. The original rocks were transformed to contorted schist and gneiss, making their original parentage almost unrecognizable.
At about 1.4 billion years ago, the metamorphic complex was injected with dikes and larger blobs of granitic magma.
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