The Earth is 4.55 billion years old, plus or minus 50 million years, as of 2014. The determination of the Earth's age is based on radiometric dating techniques involving the rate of decay of naturally occurring radioactive isotopes.
The age of the Earth has been a subject of speculation since antiquity. Aristotle believed the Earth to have existed eternally. During the 17th century, Biblical scholars estimated the age of the Earth by using the ages of people given in the Bible and extrapolating backwards. Using this method, Archbishop James Ussher of Ireland proposed a date of 4,004 B.C. for the creation of the Earth, which would make the Earth just over 6,000 years old. However, many terrestrial rocks and minerals are far older than 6,000 years, including small zircon crystals found in Western Australia that have been dated at over 4 billion years old.