Decoding Radioactive Dating and Half-Life
Delve into the intricacies of radioactive dating and half-life, exploring the concepts of isotopes, decay, and determining ages of rocks and organic material. Understand how half-life measurements can reveal the age of substances through numerical calculations based on decay rates. Discover the significance of Carbon-14 and Uranium-238 in dating processes, and unravel the mysteries behind the timeline of geological events.
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Presentation Transcript
Absolute Age 31 Jan 2022
Do Now Get out ESRT During what period did the Cryptolithus exist? When did the Alleghenian orogeny occur? When did coral reefs appear?
Ordovician Pennsylvanian or about 299 MYA Ordovician or about 466 MYA
Where did the numbers on the timeline come from? Absolute Age includes a number and unit Time comes from radio-active dating
Get out a coin Flip it What are the odds you get a head? 50 - 50 As the number of flips increase the likelihood of half the flips being heads increases (1/2)n When looking at radioactive dating you are look at hundreds of billions of flips
Dating with Carbon-14 - Used to date most recent organic material - Shortest half-life. Good for human history Dating with Uranium-238 - Used to date rocks as old as the earth itself. ESRT pg 1
Fraction 1/2 1/4 1/8 1/16 1/32 Lives 1 2 3 4 5
Radioactive decay occurs when the nuclei of unstable atoms breakdown giving off energy and particles Changes the atoms into another element Isotopes are atoms of the same element with a different number of neutrons Half life the length of time it takes 50% or half of a radioactive element to change into its stable daughter product
Using Half-life If you multiply the number of half-lives by the length of a half-life you can find the number of years that has past If two half-lives of carbon 14 have gone, how many years have gone by? 11400 years If one half-life of uranium has gone by, how old is the rock? 4.5 X 109 years
EXAMPLE If you can see in a sample of burnt wood there is one quarter C14 and three quarters N14, the sample must have gone through how many half- lives?
EXAMPLE: You Try . . If you can see in a rock sample there is 1/16th of C14 remaining, the sample must have gone through ________ half-lives and is ___________ yrs old.
EXAMPLE: You Try . . If you can see in a wood sample there is 1/16th of C14 remaining, the sample must have gone through ___4_____ half-lives and is ___________ yrs old. X X1/2 X = 1/16
EXAMPLE: You Try . . If you can see in a wood sample there is 1/16th of C14 remaining, the sample must have gone through ___4_____ half-lives and is _________ years old. 22800 X X1/2 X = 1/16 4 X 5700 years = 22800 years
If there are 4 grams of Carbon-14 and 4 grams of Nitrogen-14, the ratio is one to one I started with 8 grams of carbon-14 4g/8g = One half live has gone by To get the years I multiply the number of half lives by the length of one half life 1 X 5700 years =5700 years
If there is 2 grams of Potassium-40 and 6 grams of Argon-40, how many years have gone by? Add the grams to get the original total 2g+6g = 8g 2g/8g = = X = two half lives 2 X the half life of Potassium-40 2 X 1.3 X109 years 2.6 X109 years
Isotopes The number of protons identify the element. - Chemical elements have several forms. - Same number of protons and different Number of neutrons.
EXAMPLE Stable Element, Carbon-12: -6 Protons -6 Neutrons Unstable Element, Carbon-14: -6 Protons -8 Neutrons Carbon-14 will change into a stable element Nitrogen 14
Radioactivity is the spontaneous decay of certain unstable atomic nuclei.
Basic Atomic Structure PROTONS are positive and in the nucleus Bohr s Model of the atom NUETRONS are neutral and in the nucleus ELECTRONS are negative and orbit around the nucleus.
Half Life: - time required for half of the atoms in a sample of radioactive element to decay.
Absolute Age : - Using numbers and units to tell exactly when an event occurred. - This can be done by using fossils. Relative Age ONLY shows the order, or sequence, of events. It is a comparison
Subatomic Particles What are the three subatomic particles? Proton in nucleus Neutron in nucleus Electron in orbit around the nucleus Bohr s Model of the Atom The number of Protons determine the identity of the element Carbon has 6 protons Nitrogen has 7 protons Uranium has 92 protons
