With a circumference of 24,092 miles (40,075 kilometers) at the equator, Earth seems like a big enough planet for people, animals and plants to share. But according to the American Association for the Advancement of Science, humans are using about half the available land.
Eleven percent has become farmland, and another 11 percent is used for forestry. Twenty-six percent of the land has become pasture. Another piece, 2 or 3 percent, houses people's homes, businesses, transportation and other services we use to live and work.
All that expansion comes at a price: Habitat loss is the No. 1 contributor to extinction.