Earth is unique in that scientists have found the planet to be the only one to have liquid water on its surface, intelligent life forms living on it, a moon that helps regulate surface temperatures, an atmosphere with 21 percent oxygen and plate tectonics, according to Space.com. Scientists believe Earth exists in a "Goldilocks zone" where conditions are just right to support life.
Liquid water allowed life to evolve on Earth billions of years ago. Plate tectonics help keep water in liquid form while the carbon-silicate cycle keeps the right amount of carbon in the atmosphere. This atmospheric carbon keeps the Earth warm enough to maintain copious amounts of liquid water on its surface.
Thus far, scientists have been unable to detect intelligent life on other planets and believe that human beings are the only intelligent life in the universe. In the solar system, Earth is the only planet that harbors any type of life.
Most living things on the planet require oxygen to survive. Earth is the only place scientists know of with enough oxygen in its atmosphere to support life. The closest planets to Earth are either too hot or too cold to support an oxygen-filled atmosphere.
Using telescopes, scientists have detected many exoplanets outside of the solar system. The chances of finding Earth-like planets in the future might increase with new technology.