Geologic History: Absolute Dating Unit 6 Absolute Age

Do Now: Define the following: Define the following: ABSOLUTE AGE ABSOLUTE AGE RADIOACTIVE DECAY RADIOACTIVE DECAY HALF LIFE HALF LIFE RADIOACTIVE ISOTOPES RADIOACTIVE ISOTOPES RADIOMETRIC DATING RADIOMETRIC DATING

Absolute Dating OR Radiometric Dating Used to determine the actual age of the rock Used to determine the actual age of the rock Is an exact number (numerical age) Is an exact number (numerical age) Includes the number and unit Includes the number and unit Certain elements experience radioactive decay-we use these elements to find the absolute age of something… Certain elements experience radioactive decay-we use these elements to find the absolute age of something… Recall: Relative Age is a comparative age (older or younger )

Radioactive decay This is the spontaneous and natural breakdown from unstable to stable atomic forms This is the spontaneous and natural breakdown from unstable to stable atomic forms During this process energy is released During this process energy is released The process has a constant and predictable rate UNAFFECTED by environmental changes The process has a constant and predictable rate UNAFFECTED by environmental changes Elements that experience this are called radioactive isotopes Elements that experience this are called radioactive isotopes

Radioactive Isotope Unstable form of an element which has a different number of neutrons in their atomic nuclei Unstable form of an element which has a different number of neutrons in their atomic nuclei When it breaks down to a stable form, it creates what is known as a decay product When it breaks down to a stable form, it creates what is known as a decay product

Half-Life The time it takes a radioactive isotope to decay to half its original amount The time it takes a radioactive isotope to decay to half its original amount Occurs at a predictable rate Occurs at a predictable rate Decay Rates are found in your ESRT on front cover Decay Rates are found in your ESRT on front cover

Unstable-  to stable forms

Using Half-life to find age If you can calculate the number of half-lives, you can determine the age of the item.If you can calculate the number of half-lives, you can determine the age of the item. For example:For example: How old is a fossil that has undergone 3 half-lives of Carbon-14?

Using the Ratio to find the age: To know: 1.The older something is, the less radioisotope is in it, and the more decay product 2.Each time it decays by half of what is remaining. 3. Think of the M &M Lab

Radioactive Isotopes: Carbon-14 decays into nitrogen-14 decays into nitrogen-14 used to date once living things used to date once living things Can be used to date things as old as 54,000 years Can be used to date things as old as 54,000 years After that time not enough carbon-14 left to accurately date object After that time not enough carbon-14 left to accurately date object

Radioactive Isotopes: K-40 Potassium-40 decays into stable Argon-40 Potassium-40 decays into stable Argon-40 Used for rocks, fossils Used for rocks, fossils Used for old object- 1,300,000,000 ya Used for old object- 1,300,000,000 ya

Radioactive Isotopes: U-238 Uranium-238 decays into stable lead-206 Uranium-238 decays into stable lead-206 Used to date very old rock and very old fossils up to and over 4,600,000,000 ya Used to date very old rock and very old fossils up to and over 4,600,000,000 ya

Radioactive Isotopes: Rb-87 Rubidium-87 decays into Strontium-87 Rubidium-87 decays into Strontium-87 Used to date extremely old rock and extremely old fossils Used to date extremely old rock and extremely old fossils

Sum-Up What are radioactive isotopes? What are radioactive isotopes? What is half-life? What is half-life? How can we use radioactive isotopes to date rock? How can we use radioactive isotopes to date rock? What is absolute age? What is absolute age?