Radiometric Dating
(1907) Discovered how to calculate the age of a rock by measuring the rate of its radioactive decay. His observations and calculations put Earth's age at 2.2 billion years. Although we now think the Earth is nearly twice that age, this number was a dramatic increase over the accepted age at the time. Boltwood's formulas are compatible with several radioactive elements, including carbon14, which has been used to date historical artifacts. 
