What is It Earth is the only place in the known universe confirmed to host life and is the only one known for sure to have liquid water in the surface. These are reasons why planet Earth is a unique one: (1) It has liquid water; (2) surface or lithosphere which includes the crust and the upper mantle; and (3) It has atmosphere that shelters it from the worst of the sun's rays. Earth is the only planet in the solar system that has a large amount of liquid water. About 70% of the surface of the Earth is covered by liquid or frozen water. Because of this, Earth is sometimes called "blue planet." Planet Earth is habitable because it has the right distance from the sun. It is kept warm by an insulating atmosphere, and it has the right chemical ingredients for life including water and carbon. It can provide water, oxygen, useful biological products for human, and has suitable weather and climate. Earth, Venus, and Mars may have similarities: (1) They all are terrestrial planets, made of solid rocks and silicates; (2) They all have an atmosphere; (3) They all almost have the same time to rotate on their axes; (4) Earth and Mars both have water; (5) They all have carbon dioxide; and (6 All have landforms. Earth, Venus, and Mars have differences: (1) Venus has no water, (2) Venus and Mars don't have oxygen; and (3) Earth has life forms.​