AS101 Study Guide - Midterm Guide: Radiometric Dating
Document Summary
The most basic way is through radioactive dating. Simply put, we know the original proportion of elements in the earth"s rocks because they were sealed at these levels when the rock solidified. Some elements are radioactive and decay into daughter elements with a specific half-life. The half-life of a radioactive element is the time it takes for half of its atoms to decay. Uranium-238 has a half-life of 4. 5 billion years, as an example. The oldest earth rocks found so far have been determined to be about 4. 4 billion years old. Moon rocks, returned by the apollo astronauts, are 4. 48 billion years old. Meteorites from outer space which have landed on earth have been measured at 4. 56 billion years. Thus, it appears that our solar system formed about 4. 6 billion years ago. Note that here we are talking about billions of years - not millions.
