Question
How old is the earth?
Answer
<FONT face="Times New Roman" size=4>The age of the Earth is 4.54 billion years. This age is based on the lead isotopic composition of ancient lead ores and an iron meteorite. The age is thus the age of the Earth-meteorite system. Lead isotopes are radiogenically produced by the decay of radioactive uranium and thorium. Both Pb-ores and the iron meteorite have a large amount of lead and little uranium or thorium. Consequently, the moment they are formed the "freeze in" their lead isotopic composition. By studying the most ancient ores and assuming the meteorite and the Earth are related we can determine the age of the Earth very accurately. There is a very good book on the age of the earth by Brent Dalrymple: The age of the Earth, ISBN 0-8047-1569-6, Stanford University Press 1991. This book is the result of his expert witness testimony for trials in late 70's early 80's that tried to have creationism being taught in the science curriculum. It is written for non-scientists.<BR><BR><FONT face=Arial>Dr. Vincent J.M. Salters<BR>National High Magnetic Field Laboratory and Department of Geological Sciences<BR>Florida State University</FONT><BR></FONT>
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