All places on Earth are made of, or are on top of, rocks. The outside of the Earth is usually not uncovered rock. Over 70% of the Earth is covered by seas full of salty water. This salty water makes up about 97% of all Earth's water. The fresh water people can drink is mostly ice. Only a very small amount is in rivers and under the Earth for people to drink and use. The air above the Earth stops the water from going away into outer space. Also, much of the land on Earth is covered with plants, or with what is left from earlier living things. Places with very little rain are dry wastes called deserts. Deserts usually have few living things, but life is able to grow very quickly when these wastes have rainfall. Places with large amounts of rain may be large woods. Lately, people have changed the environment of the Earth a great deal.