Videos radiometric dating
Segment from A Science Odyssey: "Origins."Geologists have calculated the age of Earth at 4.6 billion years.But for humans whose life span rarely reaches more than 100 years, how can we be so sure of that ancient date? Even the Greeks and Romans realized that layers of sediment in rock signified old age.Relative age dating also means paying attention to crosscutting relationships.Say for example that a volcanic dike, or a fault, cuts across several sedimentary layers, or maybe through another volcanic rock type.
Sir John Herschel (1792-1871), a nineteenth century Victorian elitist, argued for “many thousand millions of years” for the age of the earth; an argument that paralleled the then popular uniformitarian theory advanced by the English geologist Charles Lyle.By measuring the ratio of uranium-235 to lead, scientists can calculate the age of the rock. Geologist Ralph Harvey and historian Mott Greene explain the principles of radiometric dating and its application in determining the age of Earth.As the uranium in rocks decays, it emits subatomic particles and turns into lead at a constant rate.Measuring the uranium-to-lead ratios in the oldest rocks on Earth gave scientists an estimated age of the planet of 4.6 billion years.