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Precambrian Rocks
11 nearly half of the valuable mineral deposits in the world occur in the rocks of this period. 15 coal deposits form -
Period: to
J. Ramos Pd.3
Geological Timescale -
Precambrian Life
10 the presence of stromatolites indicates that shallow seas cover much of Earth during intervals in this period. -
Cambrian Period
30 colonies of tiny invertebrates call graptolites flourished and vertebrates appear, fish did not have jaws or teeth and their bodies were covered with bony plates
