First of all, sex is a type of sexual reproduction. It’s meiosis. In meiosis, it has different stages and one of those stages is called Prophase 1. In prophase 1, genetic variation occurs.
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The first layer is the crust, a skin of rock covering the planet. The core that Lehman had found was the Earth's inner core. The core that Richard Oldem had discovered turned out to be the Earth's outer core.
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