Evolution – Radiometric Dating Evidence The present is the key to the past James Hutton Geologist that proposed the idea of deep time

What is Evolution ? Theory supported by evidence Biological evolution - changes in living organisms Sharing of common ancestors (branched tree of life) Darwin term: descent with modification Think: With your table buddy discuss and list at least four concepts learned that support the theory of evolution.

Radiometric Dating

Relative Dating Compares fossils & rock layers to show “age” Older fossils and rocks are generally deeper

Radiometric Dating Absolute /actual More precise Decay of UNSTABLE radioisotopes from unstable parent to stable daughter (Example Uranium to lead in Zircon) Isotopes release energy particles at a rate specific for each isotope. Half-life- amount of time it takes for half the original (parent) isotope to decay (to daughter)

Bullet what this graph shows!

Radiometric Dating Supports Evolution decay, at known, predictable rates. Pairing: Parent isotope to daughter atom varying half-lives of different isotopes allow cross referencing. Confirming different techniques Repeatable

Don’t make this too difficult! Steps 1) Determine the percent parent isotope remaining 2) Use the graph to find the number of half-lives 3) Multiply half-life from graph x number of half- life for isotope to find how old the sample is. After one half-life how much of a parent isotope would be remaining?

After 2 half-lives how much of the parent isotope is remaining?

Question After Three half-lives, what percent of the parent isotopes remain?

Do Practice Problems: Steps 1) Determine the percent of parent isotopes remaining. 2) Use the graph determine half-lives that the isotope has gone through 3) Multiply the half-lives by the known half- life for that isotope

Answer Question # 1 An original rock with 60 atoms of Uranium 238. Half-life is 4.5 billion years After one half-life, how old is the sample How many atoms are remaining? After two half-lives, how many parent atoms are remaining?

Question #2: A sample has 5 atoms of radioactive (parent) uranium 235 remaining and 65 (daughter) atoms of lead (Pb) present. a) What percentage of radioactive isotopes remaining? b) Graph reads: c) half-life of uranium 235 is 704,000,000 million years so the age of the sample is

Question 3: If an element has a half-life of twenty million years and there is 6.25% parent isotope remaining, how old is the rock? Graph Read from Y axis 6.25% remaining: Multiply 4 half lives X 20,000,000 years =

Question 4: The radioactive isotope carbon 14 is used to date a once living organism. Carbon 14 has a half-life of 5730. If there are 20 atoms of parent isotope and 5 of daughter isotope remaining, what is the age of the fossil. Steps: Determine % of parent isotopes remaining: Step: Number of half lives: Multiply the number of half-lives X half life

Question #5: Potassium 40 can also be used to date biological fossils since potassium is found in living organisms. Potassium 40 has a half life of 1.28 billion years and decays to argon. If 5% of original isotope is remaining use the graph to find the number of half-lives the sample has completed. Multipy the half lives 4.1 X 1.28 billion years to find

Question #6: Uranium 238 has a half life of 4. 5 billion years Question #6: Uranium 238 has a half life of 4.5 billion years. If you have 20 atoms of uranium 238, how many are remaining after one half life? 10 Uranium 238 isotopes remain and 10 will now have been converted into daughter atoms. After one more half-life how many will remain?

Question 7: Rubidium-87 has a half-life of 48. 8 billion years Question 7: Rubidium-87 has a half-life of 48.8 billion years. 100 atoms of rubidium decays into daughter atoms and now 25% remain. How many atoms are remaining? How many half-lives has rubidium gone through: What is the age of the fossil