Earth is the largest and densest of the four inner planets, the only one known to have current geological activity, like earthquakes and volcanoes. It is the only planet known to have life. Its liquid hydrosphere (oceans and seas) is unique among the terrestrial planets.
Earth's atmosphere is radically different from those of the other planets, having been altered by the presence of life so it now contains 21% oxygen - which humans need to be able to breathe!
It has one natural satellite, the Moon, which is the only large satellite of a terrestrial planet in the Solar System.
The Earth is 150,000,000 km from the sun.
