Earth is the third planet of the solar system. It is the only planet known to have life on it. Because of its water, Earth is home to millions of species of plants and animals which require water to survive. About seven billion people live on Earth. They live in about 200 different lands called countries. Some, like Russia, are large with many large cities. Others, like the Vatican, are small. The five countries with the most people are China, India, the United States, Indonesia, and Brazil. About 90% of people live in the north half of the world, which has most of the land. People change the Earth in many ways. They have been able to grow plants for food and clothes for about ten thousand years. When there was enough food, they were able to build towns and cities. Near these places, men and women were able to change rivers, bring water to farms, and stop floods from coming over their land. People found useful animals and bred them so they were easier to keep.