About 11,000 years ago, before humans learned agriculture, forests covered much of the Earth's land. Today, after widespread deforestation, forests cover only about one-fifth of the planet's surface. Deforestation occurs for many reasons like using trees for fuel, timber, or cleared land for livestock or agriculture. The large-scale removal of trees without replanting has damaged habitats and biodiversity while increasing carbon dioxide emissions and soil erosion. Currently 12 million hectares of forest are cleared annually.