Earth is the third planet from the Sun and the only object in the Universe known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.
To EU-funded Earth scientists it is evident that many parts of the Earth's crust have been extracted from the underlying mantle. However, the timing of new crust formation and recycling of old crust has proven to be an elusive issue.