Absolute Ages of Rock Mr. Perez

Important vocabulary Isotopes Radioactive decay Half-life Radiometric dating Uniformitarianism

Absolute Ages Absolute age is the age, in years, of a rock or other object. Examples: How old are you? How old is your house? How old is your book bag? How old is your pet? How old is your sibling?

Radioactive Decay Atoms are made up of: Nucleus- central region Includes the protons (+) and neutrons (0) Electrons- cloud surrounding center (-) The number of protons(+) determines the identity of the element The number of neutrons (0) determines the form of the element (aka isotope)

Radioactive Decay Some isotopes are unstable and break down into other isotopes and particles We call the above process radioactive decay

Radioactive Decay- Alpha and Beta Decay Neutron breaks down into proton and electron Electron leaves atoms a beta particle Alpha Decay Two protons and two neutrons are given off Leave as alpha particle Both types of decay form a new isotope

Radiometric Decay- Half Life Each parent isotope decays (breaks down) into its daughter isotope at a certain rate Based on this decay rate, it takes a certain period of time for one half of the parent isotope to decay to its daughter product The half-life of an isotope is the time it takes for half of the atoms in the isotope to decay. Example- It takes carbon-14 5,730 years for half of its atoms to turn into nitrogen-14. Then, it takes another 5,730 years for half of the remaining carbon-14 atoms to turn into nitrogen-14, and so on… THINK OF EXPONENTS! 23 = 8, 32 = 9, 44 = 256

Radioactive Decay- Half-life Fill in the following table using this information: Mr. Perez has 100g of carbon-14. After 5,730 years, how many grams of carbon-14 will still be carbon-14? After 2? After 3?... Year Grams of carbon-14 100g 1 2 3 4

Radiometric Dating

Radiometric Dating By measuring the ratio of parent isotope to daughter product in a mineral AND knowing the half-life of the parent, you can calculate the absolute age of a rock This is called radiometric dating A scientist must decided which parent isotope to use when measuring the age of a rock. If it’s old, the scientist will use an isotope with a long half-life Example: potassium-40 takes 1.25 billion years to decay to argon-40 To avoid errors, conditions must be met for ratios to give a correct indication of age: The rock being studied must retain ALL of the argon-40 that produced by the decay of potassium-40 It cannot contain any contamination of daughter product from other sources

Radiometric Dating- Radiocarbon Dating Carbon-14 is useful for dating bones, wood and charcoal up to 75,000 years old. Living things take in carbon from the environment to build their bodies Most of this carbon is carbon-12, but some is carbon-14 The radio of these two isotopes is always the same After an organism dies, the carbon-14 decays slowly By determining the amounts of isotopes in a sample, scientists can evaluate how much the isotope ratio differs from that in the environment

Radiometric Dating- Radiocarbon Datin

Radiometric Dating- Age Determinations The Oldest Known Rocks Rocks that can be radiometrically dated are mostly IGNEOUS and METAMORPHIC rock Sedimentary rocks cannot be dated by carbon-14 because they are made up of particles eroded from older rocks The Oldest Known Rocks Using radiometric dating, the oldest rocks on Earth are about 3.96 billion years old The Earth is about 4.5-4.6 billion years old

Uniformitarianism James Hutton (Scottish scientist in the 1700s) Estimated that the Earth is much older than we think Uniformitarianism- principle that states that Earth’s processes occurring today are similar to those that occurred in the past “The present is the key to the past” Today, scientists recognize that Earth has been shaped by two types of change Slow, everyday processes that take place over millions of years Violent and unusual events

Videos http://science.howstuffworks.com/environmental/earth/geology/carbon-14.htm http://teachertube.com/viewVideo.php?video_id=181054&title=Radioactive_decay

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