During the Ice Ages of the Quaternary Period, most of the land was covered with ice, and vegetation included mosses, sedges, shrubs, lichens and low-lying grasses. During warmer periods, most of the soil was not covered with ice, and woodlands and coniferous forests existed. The emergence of tropical rainforests occurred during the Holocene. This habitat allowed many animals and plants to thrive and evolve. Savannas also emerged where herbivores grazed and flourished.
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