EPSC 201 Lecture 20: EPSC201 Lecture 20 Notes.doc
11 Mar 2013
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In the 1600s we dated the earth using biblical sources. They thought it was around 6000 years old. In the 1800s, lord kelvin and other physicists tried to calculate how long the earth would take to cool, assuming the earth started out as molten. Kelvin figured the earth was around 100 million years old (last lecture said 400 million years old). Wikipedia says the kelvin initially calculated the earth to be between 20 to 400 millions years old, but eventually settled on 20-40 mil- lion years old. Lord kelvin, and other physicists, did not account for radioactive forces. As elements decay, they re- lease heat in the form of alpha particles, which are absorbed by the rocks in the earth, and are heat- ed. He showed that elements have a constant rate of radiation decay. Rutherford made several estimates using uranium and lead decay. The oldest rocks in canada range from 3. 8 to 4. 2 billion years old.
