Mollisol

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Mollisol is a soil type which has deep, high organic matter, nutrient-enriched surface soil (a horizon), typically between 60 and 80 cm (24–31 in) in depth. This fertile surface horizon, called a mollic epipedon, is the defining diagnostic feature of Mollisols. Mollic epipedons are created by long-term addition of organic materials derived from plant roots and typically have soft, granular soil structure. Mollisols typically occur in savannahs and mountain valleys (such as Central Asia, and the North American Great Plains). These environments have historically been strongly influenced by fire and abundant pedoturbation from organisms such as ants and earthworms. It was estimated that in 2003, only 14 to 26 percent of grassland ecosystems remained in a relatively natural state (that is, they were not used for agriculture due to the fertility of the horizon). Globally, they represent ~7% of ice-free land area. As the world's agriculturally most productive soil order, the Mollisols represent one of the most economically important soil orders. Though most other soil orders known today were formed at the beginning of the Carboniferous Ice Age 280 million years ago, Mollisols are best known from the paleopedological record possibly as early as the Maastrichtian, though confidently found in the Eocene. Their development is very closely associated with cooling and drying of the global climate that occurred during the Oligocene, Miocene and Pliocene.