The Proterozoic, or the Age of First Life, encompasses most of the history of earth, from the time of the oldest preserved fossils to the Cambrian explosion. In general, the fossil organisms are less complex than those found later in life, and the preserved ecosystems are also simpler than later life assemblages. Such economically important deposits as the various Banded Iron formations, and biologically important deposits as the first stromatolites, are Proterozoic in age.
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