Absolute Dating Chapter 7 Lesson 2

Absolute Dating Main Idea Unstable parent isotopes change to stable daughter isotopes at a constant rate. Geologists measure the amounts of these isotopes in minerals to determine how long ago the minerals formed which is called Absolute Dating.

Isotopes Atoms of the same element that have the same number of protons but have a different number of neutrons are called isotopes. Most isotopes are stable , meaning they stay in their original form. But some isotopes are unstable-we call these radioactive.

The more daughter isotope there is the older the rock is. Radioactive Decay The breakdown of a radioactive, unstable isotope (parent) of one element into a stable isotope (daughter) of another element is called radioactive decay. Scientists compare the amount of parent isotope with the amount of daughter isotope to determine the absolute age of a rock. The more daughter isotope there is the older the rock is.

Half Life & Radiometric Dating Radiometric dating is finding the absolute date of a rock using radioactive decay and the half life of an isotope. A half life is the time it takes for one- half of a radioactive, unstable parent isotope to decay by ½ into daughter isotopes.

2 Forms of Radiometric Dating Potassium-40 Potassium 40 has a half life of 1.3 billion years. It decays to 2 other stable elements called argon and calcium. This is used to date rocks older than 100,000 years old. Uranium-238 Uranium-238 is a radioactive isotope that decays to lead-206. Uranium-238 has a half life of 4.5 billion years. This is used to date rocks older than 10 million years

Half Dome Using Uranium-238 to measure the ignous rock of half dome determined that Half Dome in Yosemite formed about 85 million years ago.

The Earth and our Solar system are about 4.6 billion years old Age of Earth Even though there are no rocks on earth that we can measure the date that are from when the Earth was formed, rocks from our solar system, the moon, and from meteorites have been measured. The Earth and our Solar system are about 4.6 billion years old