Some scientists have suggested the idea of a galactic habitable zone (GHZ). This habitable zone is the region of a galaxy in which life is most likely to develop. In particular, the notion of a GHZ includes factors such as the rate of potentially life-threatening major cosmic events, like supernovae, and an idea known as metallicity—the fraction of chemical elements that is not hydrogen and helium. These factors help in the experts’ calculation of which regions of the Galaxy are best suited to forming Earth-like planets, or to evolve suitable environments for life to advance. And yet, more
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