Tropical rainforest

A tropical rainforest is an ecosystem type that occurs roughly within the latitudes 28 degrees north or south of the equator (in the equatorial zone between the Tropic of Cancer and Tropic of Capricorn). This ecosystem experiences high average temperatures and a significant amount of rainfall. Rainforests can be found in Asia, Australia, Africa, South America, Central America, Mexico and on many of the Pacific, Caribbean, and Indian Ocean islands. Within the World Wildlife Fund's biome classification, tropical rainforests are thought to be a type of tropical wet forest (or tropical moist broadleaf forest) and may also be referred to as lowland equatorial evergreen rainforest. Tropical rainforests can be characterized in two words: warm and wet. Mean monthly temperatures exceed 18 C (64 F) during all months of the year.[4] Average annual rainfall is no less than 168 cm (66 in) and can exceed 1,000 cm (390 in) although it typically lies between 175 cm (69 in) and 200 cm (79 in).[5] This high level of precipitation often results in poor soils due to leaching of soluble nutrients. Tropical rainforests are unique[citation needed] in the high levels of biodiversity they exhibit. Around 40% to 75% of all biotic species are indigenous to the rainforests.[6] Rainforests are home to half of all the living animal and plant species on the planet.[7] Two-thirds of all flowering plants can be found in rainforests.[5] A single hectare of rainforest may contain 42,000 different species of insect, up to 807 trees of 313 species and 1,500 species of higher plant

.[5] Tropical rainforests have been called the "jewels of the Earth" and the "world's largest pharmacy", because over one quarter of natural medicines have been discovered within them.[8] It is likely that there may be many millions of species of plants, insects and microorganisms still undiscovered in tropical rainforests. Tropical rainforests are among the most threatened ecosystems globally due to large-scale fragmentation due to human activity. Habitat fragmentation caused by geological processes such as volcanism and climate change occurred in the past, and have been identified as important drivers of speciation.[9] However, fast human driven habitat destruction is suspected to be one of the major causes of species extinction. Tropical rain forests have been subjected to heavy logging and agricultural clearance throughout the 20th century, and the area covered by rainforests around the world is rapidly shrinking. Tropical rainforests have existed on Earth for hundreds of millions of years. Most tropical rainforests today are on fragments of the Mesozoic era supercontinent of Gondwana.[12] The separation of the landmass resulted in a great loss of amphibian diversity while at the same time the drier climate spurred the diversification of reptiles.[9] The division left tropical rainforests located in five major regions of the world: tropical America, Africa, Southeast Asia, Madagascar, and New Guinea, with smaller outliers in Australia.[12] However, the specifics of the origin of rainforests remain uncertain due to an incomplete fossil record.