Radiometric dating and the age of Earth

Relative dating puts rock layers and events in order using principles like superposition (in undisturbed layers, older rocks lie below younger ones), cross-cutting relationships (a fault or intrusion is younger than the rock it cuts), and index fossils, but it cannot give an age in years. Radiometric, or absolute, dating can. A radioactive parent isotope decays into a stable daughter isotope at a constant rate, described by its half-life, the time it takes for half of the parent atoms in a sample to decay. By measuring the ratio of parent to daughter atoms in a mineral, scientists calculate how long ago it formed: after one half-life, 50 percent of the parent remains; after two, 25 percent; after three, 12.5 percent. Different isotopes suit different ages: carbon-14, with a half-life of about 5,730 years, dates once-living material up to about 50,000 years old, while uranium-lead dating (uranium-238 has a half-life of about 4.5 billion years) and potassium-argon dating work for ancient rocks. Radiometric dating works best on igneous rocks, whose minerals start the clock when they crystallize; sedimentary layers are usually dated by bracketing them between datable volcanic layers, and results are checked by using more than one method on the same rock. These methods show that the oldest known Earth minerals, zircon crystals from Australia, are about 4.4 billion years old, the oldest rocks are about 4 billion years old, and meteorites and Moon rocks are about 4.5 billion years old, giving Earth an age of about 4.54 billion years, often rounded to 4.6 billion.

This explanation is AI-generated and can occasionally be wrong. 🚩 Report