Absolute dating com
But it wasn't until the late 1700s -- when Scottish geologist James Hutton, who observed sediments building up on the landscape, set out to show that rocks were time clocks -- that serious scientific interest in geological age began.Before then, the Bible had provided the only estimate for the age of the world: about 6,000 years, with Genesis as the history book.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.For teaching and sharing purposes, readers are advised to supplement these historic articles with more up-to-date ones suggested in the Related Articles and Further Reading below.Before 1955, ages for the Earth based on uranium/thorium/lead ratios were generally about a billion years younger than the currently popular 4.5 billion years. old Earth is reviewed and deficiencies of the uranium/lead method are discussed.Thanks to the consistency of natural radioactive decay, science has found a measuring tool for seemingly unmeasurable amounts of time.
Before this and other 'absolute' dating methods, scientists could only determine the relative or chronological ages of samples.This rate of decay is constant for a given isotope, and the time it takes for one-half of a particular isotope to decay is its radioactive half-life.For example, about 1.5 percent of a quantity of Uranium 238 will decay to lead every 100 million years.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.