1. The Age of The Earth Moving towards the billion years old concept.

2. Techniques 1860: Average Sedimentation Rate Age: 3 million years: Highly faulty method as it does not account for past erosion and large variability in sedimentation rates. 1897: Lord Kelvin assumes earth is initially molten and would take 20-40 million years to cool. 1899: Joly uses ocean salinity and delivery rate from streams to calculate 90-100 million years. So by 1900, a reliable age still eludes us

3. Radioactive Methods 1896: Becquerel discovers radiation. 1905: Rutherford and Boltwood uses Uranium decay to Helium to measure 500 million years for the oldest rocks. But, how do you know where the oldest rocks are? 1907 Boltwood believes that Lead (not Helium) is the stable end point for Uranium decay and now gets 1.64 Billion years as the Age.