Earth is the third planet from the Sun, orbiting between Venus and Mars. It is also the only planet known to humans to have life. It is the fifth largest planet in the solar system and the largest terrestrial planet in the solar system as well. It has mild temperatures and 70% of the planet's surface is covered in water, which is where life started 3.8 billion years ago. Its atmosphere protects it from space radiation, contains oxygen for its inhabitants to breath and keeps the right amount of heat close to the planet's surface. The planet is also tilted which results in the four seasons that occur on the planet. The areas with more sun and heat are summer, and the less sun illuminated areas are winter. Earth has only one moon, which is known as the Moon in English.