Earth is an oasis of life in an this desolate universe. The Earth's temperature, weather, atmosphere and many other factors are just right to keep us alive. The Earth is the biggest of all the terrestrial planets. A terrestrial planet is a dense planet found in the inner Solar System.
Scientists use the Earth to study all the other planets. Since no human has been able to visit another planet, we use what we know about the Earth, and try to guess what the other planets must be like. This study is called Comparative Planetology.