radioactive dating
Things Great and Small Nuclear Decay Helps Explain Earths Hot Interior A puzzle created by radioactive dating of rocks is resolved by radioactive heating of Earths interior. This intriguing story is another example of how small-scale physics can explain large-scale phenomena. Radioactive dating plays a role in determining the approximate age of the Earth. The oldest rocks on Earth solidified about 3.510 9 years agoa number determined by uranium-238 dating. These rocks could only have solidified once the surface of the Earth had cooled sufficiently. The temperature of the Earth at formation can be estimated based on gravitational potential energy of the assemblage of pieces being converted to thermal energy. Using heat transfer concepts discussed in Thermodynamics it is then possible to calculate how long it would take for the surface to cool to rock9 9 formation temperatures. The result is about 10 years. The first rocks formed have been solid for 3.510 years, so that 9 the age of the Earth is approximately 4.510 years. There is a large body of other types of evidence both Earth-bound and solar system characteristics are used that supports this age. The puzzle is that, given its age and initial temperature, the center of the Earth should be much cooler than it is today see Figure 31.26 .