The Earth is the only habitable planet in the solar system. Why did life begin only here? The answer lies in the suitability of both the size of the Earth and the distance between it and the Sun. These two factors together have created the tremendously wonderful conditions for life as we know it. The conditions required for living creatures to prosper include water, air and mild temperatures. Life wouldn't have begun without all these conditions being in place. The Earth is a miraculous and irreplaceable planet.