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This four-celled animal embryo was extracted from 600 million-year-old rocks in Guizhou Province, South China. The cells, magnified using a scanning electron microscope, are about 0.65 millimeters in diameter. Research by Shuhai Xiao, a professor of geobiology at Virginia Tech, has found evidence that animals may have existed before the Cambrian period (542 to 488 million years ago) in the Precambrian period, which spans from 4.
5 billion years ago to the beginning of the Cambrian period.Image credit: Shuhai Xiao
