Tropical rainforests are rainforests that are found near the equator and have high average temperatures and high humidity. They feature extreme biodiversity, estimated to contain roughly half of the total species of terrestrial organisms, despite the fact that they cover only about six percent of the earth's surface. This contrasts with temperate rainforests, which occur mainly in coastal, mountainous areas in the mid-latitudes, and are far less biologically diverse. There are likely millions of species, particularly of plants, insects and microorganisms, that remain undiscovered in tropical rainforests.