Forming around 4.5 billion years ago, the Earth is the third planet from the Sun. It is one of the four terrestrial planets in our Solar System, meaning that most of its mass is solid. The other three are Mercury, Mars, and Venus. However, Earth is the only place in the Solar System where liquid water is known to exist, with 71% of Earth's surface is covered in salt water oceans while the other 29% is made of rocky land of continents and islands.

The Earth interacts with other objects in the Solar System, particularly the Sun and the Moon. The Earth rotates on its axis, with one spin being called a day and the Earth orbits around the Sun once every 365.25 days, called a year. Thus, there are 365 days in a year, but an extra day (leap day) is added once every 4 years (leap year).

The Earth is home to millions of species of plants and animals, including humans, and these organisms have completely changed its atmosphere.