Rainforests are very dense, warm, wet forests. They are havens for millions of plants and animals. The plants of the rainforest generate much of the Earth's oxygen. These plants are also very important to people in other ways; many are used in new drugs that fight disease and illness. It is almost always raining in a rainforest. Rainforests get over 2 m. of rain each year. This is about 3.8 cm of rain each week. The range of temperature in a tropical rainforest is usually between 24-27 C. An incredible number of animals live in rainforests. Millions of insects, reptiles, amphibians, birds, and mammals call them home. Insects are the most numerous animals in rainforests.