Radiometric dating uses what isotopes
After all, textbooks, media, and museums glibly present ages of millions of years as fact.Yet few people know how radiometric dating works or bother to ask what assumptions drive the conclusions.Orbiting around the nucleus are electrons (tiny particles each with a single negative electric charge).The atoms of each element may vary slightly in the numbers of neutrons within their nuclei.It is the interpretation of these chemical analyses that raises potential problems.To understand how geologists “read” the age of a rock from these chemical analyses, let’s use the analogy of an hourglass “clock” (Figure 2).So let’s take a closer look and see how reliable this dating method really is.Each chemical element, such as carbon and oxygen, consists of atoms.
Most people would assume that the “clock” started half an hour earlier.
Examples are granites (formed by cooling under the ground) and basalts (formed by cooling of lava at the earth’s surface).
The next step is to measure the amount of the parent and daughter isotopes in a sample of the rock unit.
These parent radioisotopes change into daughter lead-206, lead-207, argon-40, strontium-87, and neodymium-143 isotopes, respectively.
Thus geologists refer to uranium-lead (two versions), potassium-argon, rubidium-strontium, or samarium-neodymium dates for rocks.
Some isotopes are radioactive; that is, they are unstable because their nuclei are too large.