metagenesis Following catagenesis, a phase in the formation of petroleum and natural gas during which the temperature rises above 150 °C and may exceed 200 °C, causing destruction of kerogen and release of gas (mainly methane); at the higher temperatures petroleum is destroyed, leaving only natural gas.
metagenesis The occurrence, during the life cycle of an organism, of two types of individual, both diploid, both of which reproduce, one sexually and the other asexually. The term is sometimes used loosely (but incorrectly) as a synonym for the alternation of generations. For example, the life cycle of hydrozoans (e.g. Obelia geniculata) comprises an asexual sedentary generation followed by a sexual medusoid generation, both of which are diploid. The medusoid individuals then become sedentary (and asexual).
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