How old is the Earth? This lecture reviews the idea of cyclic and

linear time, since how you view time determines whether the question of

the age of the Earth is even meaningful. We then review various ways

people have estimated the age of the Earth, starting with historical

ages that equate human history with the history of the Earth proper, and

then see how various physical estimates, which do not make an appeal to

human history, were made. This brings us to the technique of

radioactive age dating of the oldest rocks, leading to our current best

estimate of 4.5+/-0.1 Billion years for the age of our planet. Recorded

2006 Oct 30 in 100 Stillman Hall on the Columbus campus of The Ohio

State University.