Radiocarbon dating is one kind of radiometric dating, used for determining the age of organic remains that are less than 50,000 years old.
For inorganic matter and for older materials, isotopes of other elements, such as potassium, uranium, and strontium, are used.
The amount of the isotope in the object is compared to the amount of the isotope's decay products.
The object's approximate age can then be figured out using the known rate of decay of the isotope.
Find additional lessons, activities, videos, and articles that focus on relative and absolute dating.
Radiometric dating (often called radioactive dating) is a way to find out how old something is.
A breakthrough came with the discovery of radioactivity at the beginning of the 1900s.
Scientists discovered that rocks could be timepieces -- literally.
Using fossils as guides, they began to piece together a crude history of Earth, but it was an imperfect history.
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.
So in order to date most older fossils, scientists look for layers of igneous rock or volcanic ash above and below the fossil.
Scientists date igneous rock using elements that are slow to decay, such as uranium and potassium.