Uses of uranium lead dating
The method relies on the coupled chronometer provided by the decay of 238U to 206Pb, with a half-life of 4.46 billion years and 235U to 207Pb, with a half-life of 704 million years.
One of the advantages of uranium-lead dating is the two separate, chemically identical chronometers and is accepted as the most reliable measurement of the age of the Earth.
The in situ U-Pb technique involves laser ablation to remove minute particles of the fossil which then undergo isotopic analysis.
The results have now been published in Geology, the journal of the Geological Society of America.
The presence of minerals or zones within minerals, older than the rock being dated can also cause age-discordance.
In either case, the geochronologist is warned that such uranium-lead ages cannot be taken at face value.
Yet this view is based on a misunderstanding of how radiometric dating works.
Part 1 (in the previous issue) explained how scientists observe unstable atoms changing into stable atoms in the present.
Uranium-238, for example, accounts for more than 99 percent of all naturally occurring uranium. A fertile material, not itself capable of undergoing fission with low-energy neutrons, is one that decays into fissile material after neutron absorption...However, such methods are far from perfect: it is difficult to gain accurate depositional ages for sedimentary rocks, and matters can be further complicated when millions of years of geologic and environmental forces cause erosion of fossil-bearing strata.Fossils can even migrate from their original positions within strata....species with the same atomic number but different mass numbers), decay with time.These include elements with an atomic number greater than 83—of which the most important are uranium-235, uranium-238, and thorium-232—and a few with a lower atomic number, such as potassium-40.
A Canadian research team has used a new uranium-lead (U-Pb) dating technique to show that a fossilised dinosaur bone found in New Mexico is only 64.8 million years old, meaning the creature was alive about 700,000 years after the mass extinction event that is believed to have wiped out all non-avian dinosaurs.