The Earth's rainforests have been given well-deserved nicknames, such as "lungs of the planet" and "cradles of biodiversity." Tropical rainforests cover no more than about 6 percent of the planet, yet one of the Earth's major rainforests, the Amazon rainforest in South America, is believed to produce about 20 percent of the world's oxygen, while also absorbing nearly 20 percent of the world's carbon dioxide. It is estimated that rainforest biodiversity represents more than half of the world's combined animal and plant life.
Another nickname given to rainforests is "the world's pharmacy." More than 25 percent of the world's naturally-produced medicines were first discovered in rainforests, such as quinine, a treatment for malaria, which was first derived from a rainforest plant. Well-known and much consumed food products, such as chocolate, vanilla, cinnamon and coffee, also come from rainforests.
Tropical rainforests are located in the equatorial zone, which lies between the Tropic of Capricorn and the Tropic of Cancer. In order to be considered a tropical rainforest, a region must receive more than 98 inches of rain annually and must also be free of frost throughout the year. In addition to South America, which contains about 40 percent of the world's rainforest, tropical rainforests are found in Central America, Central Africa, Southeast Asia and the Caribbean.
Rainforests have been the victim of heavy deforestation and logging. Some estimates predict that in 100 years, they will cease to exist. Brazil has declared the situation in its Amazon Rainforest to be a national emergency, and Madagascar has already been depleted of more than 60 percent of its rainforest region as of 2015. A Harvard biologist has estimated that the Earth's continuing rainforest depletion could result in about 25 percent of the world's species becoming extinct by the second half of the 21st century.