Absolute Dating

A.D. is used when geologists want to know the actual numerical age of a rock layer. A.D. is used when geologists want to know the actual numerical age of a rock layer. A.D. uses the principle of radioactive decay to find the age of rocks. A.D. uses the principle of radioactive decay to find the age of rocks.

Radioactive Decay R.D. occurs when unstable isotopes decay into stable products. R.D. occurs when unstable isotopes decay into stable products.

Radioactive Decay R.D. occurs when unstable isotopes decay into stable products. R.D. occurs when unstable isotopes decay into stable products.TRANSLATION

Radioactive Decay R.D. occurs when unstable isotopes decay into stable products. R.D. occurs when unstable isotopes decay into stable products.TRANSLATION Parent material (unstable) Turns into Daughter material (stable)

Radioactive Decay Isotopes occur naturally in rocks. Isotopes occur naturally in rocks. If we know the rate at which the decay occurs we can figure out how old the rock is. If we know the rate at which the decay occurs we can figure out how old the rock is. The rate of decay for an isotope depends on its half-life. The rate of decay for an isotope depends on its half-life.

Half-Life Half-life is the unit used to describe how long it takes the unstable parent material to decay to half its original amount. Half-life is the unit used to describe how long it takes the unstable parent material to decay to half its original amount.

Half-Life But, why half? Why not just say how long it will take until it is all gone?

Half-Life Answer: Because radioactive isotopes dont decay in a straight line.

Half-Life

Half-Life

Half-Life

Half-Life

Half-Life

But the path from Parent to Daughter isnt always the most direct one Example; the natural decay chain of uranium-238decay chainuranium-238 decays, through alpha-emission, with a half-life of 4.5 billion years to thorium-234half-lifethorium-234 which decays, through beta-emission, with a half-life of 24 days to protactinium-234protactinium-234 which decays, through beta-emission, with a half-life of 1.2 minutes to uranium-234uranium-234 which decays, through alpha-emission, with a half-life of 240 thousand years to thorium-230thorium-230 which decays, through alpha-emission, with a half-life of 77 thousand years to radium-226radium-226 which decays, through alpha-emission, with a half-life of 1.6 thousand years to radon-222radon-222 which decays, through alpha-emission, with a half-life of 3.8 days to polonium-218polonium-218 which decays, through alpha-emission, with a half-life of 3.1 minutes to lead-214lead-214 which decays, through beta-emission, with a half-life of 27 minutes to bismuth-214bismuth-214 which decays, through beta-emission, with a half-life of 20 minutes to polonium-214polonium-214 which decays, through alpha-emission, with a half-life of 160 microseconds to lead-210lead-210 which decays, through beta-emission, with a half-life of 22 years to bismuth-210bismuth-210 which decays, through beta-emission, with a half-life of 5 days to polonium-210polonium-210 which decays, through alpha-emission, with a half-life of 140 days to lead-206, which is a stable nuclide.lead-206

Half-Life To use radioactive age dating on a rock sample you must know two things: To use radioactive age dating on a rock sample you must know two things: 1.The amount of stable daughter isotope in the sample 2.The decay rate (half-life) for that isotope

Half-Life Carbon – 14 is used to find the age of organic material. Carbon – 14 is used to find the age of organic material. Its half-life is 5730 years so it is only useful dating objects less than years Its half-life is 5730 years so it is only useful dating objects less than years.

Half-Life Uranium – 238 is often used to date rocks because it is the most common type of uranium found in nature. Uranium – 238 is often used to date rocks because it is the most common type of uranium found in nature. Its half-life is 4.46 billion years Its half-life is 4.46 billion years Watch this Watch this

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