Age of the Earth

The age of the Earth is generally agreed by scientists to be 4.54 billion years (4.54*10²), plus or minus about 1%. That estimate has been made mainly through radiometric dating of Earth rocks and meteorites.

In his 1991 book, The Age of the Earth, geologist/geophysicist G. Brent Dalrymple gives two examples for visualizing a time period of 4.54 Ga (billion years):

If a piece of string 2.5 cm long (about an inch) represents one year, for example, then a 183-cm length (about 6 feet) is equivalent to the average lifetime of a person living in the United States. A string representing all of recorded human history would be fully a kilometer long, but a piece representing 4.5 billion years would be 114,280 km [71,010 miles] long! Four and one-half billion quarters would form a stack nearly 8,000 km [4,971 miles] high. Can anyone fully visualize a string that would wrap around the Earth nearly three times, or a stack of quarters that would reach from here through the center of the Earth and halfway to the other side?

Geological evidence

The main geological evidence is found from lead, as there is assumed to be none of the original crust left due to erosion.