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Our transcription: About 600 million years ago, many complex eukaryotic life forms developed with geological suddenness. Though sexual reproduction no doubt accelerated this appearance of new life, no one knows exactly why it happened. The first appearance of numerous fossils in rocks of this age marks the end of the long Precambrian Era and the beginning of the Paleozoic Era. This event is known as the "Cambrian Explosion." The preservation of these fossils was made possible by the fact that life, for the first time, included abundant hard parts.
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