Lecture 27: Deep Time - The Age of the Earth
How old is the Earth? In this lecture I review the ideas of cyclic and\nlinear time, and how this determines whether or not the question of the\nage of the Earth is meaningful. I then review various ways people have\ntried to estimate the age of the Earth, starting with historical ages\nthat equate human history with the physical history of Earth. We then\nlook at physical estimates of the Earth's age that do not make an appeal\nto human history, but instead seek physical processes that play out over time\nto make the estimates. This brings us to a discussion of radiometric\nage dating techniques that use the radioactive decay of isotopes trapped\nin minerals to identify the oldest Earth rocks and meteorites, and hence \nestablish a radiometric date for the formation of the Earth some\n4.55+/-0.05 Billion Years ago. Recorded 2007 Oct 29 in 1000 McPherson \nLab on the Columbus campus of The Ohio State University.