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The continent’s early Paleozoic rocks depict the breakup of the first supercontinent, an event probably related to the separation of eastern North America from the pre-Andean basement rocks of western South America. As a result of that separation, a series of passive continental margins developed along the western side of the continent from Venezuela and Colombia to central Argentina; essentially, the Precambrian platform amalgamated during the Brazilian cycle. The rifted margins today are represented mainly by clastic rocks from the Cambrian Period (i.e., roughly 500 million years old) bearing numerous trilobites and graptolites, as in the Cordillera Oriental of Bolivia. ...(100 of 23598 words)