Radioactive isotopes used in absolute dating
An element is defined by the number of protons it contains. For carbon-14 decay, each carbon-14 atom loses an alpha particle. This is illustrated in Figure below and at the link below.[Insert a link to an animation of the decay of carbon-14 to nitrogen-14.] The decay of an unstable isotope to a stable element occurs at a constant rate. The decay rate is measured in a unit called the half-life.
All atoms of a given element contain the same number of protons. Atoms of an element with different numbers of neutrons are called isotopes. The half-life is the time it takes for half of a given amount of an isotope to decay.
I also like this simple exercise, a spin-off from an activity described on the USGS site above.
Take students on a neighborhood walk and see what you can observe about age dates around you.
Here is an easy-to understand analogy for your students: relative age dating is like saying that your grandfather is older than you.
Absolute age dating is like saying you are 15 years old and your grandfather is 77 years old.
What’s more, if the whole rock is badly weathered, it will be hard to find an intact mineral grain containing radioactive isotopes.
No bones about it, fossils are important age markers.For example, which is older, the bricks in a building or the building itself?Are there repairs or cracks in the sidewalk that came after the sidewalk was built? Absolute ages are much different from relative ages. Absolute ages are determined by radiometric methods, such as carbon-14 dating. Radioactive decay is the breakdown of unstable elements into stable elements. But carbon-12 has 6 neutrons and carbon-14 has 8 neutrons. Neutrons in cosmic rays strike nitrogen atoms in the atmosphere. Carbon in the atmosphere combines with oxygen to form carbon dioxide.To understand this process, recall that the atoms of all elements contain the particles protons, neutrons, and electrons. Plants take in carbon dioxide during photosynthesis. Like other unstable isotopes, carbon-14 breaks down, or decays.