Presentation on theme: "Absolute Dating. J F M A M J J A S O N D J Earth Forms Earth Cools First Life Abundant Oxygen Multicellular Organisms Plants and Animals Dinos 15-25 Humans."— Presentation transcript:
Parent/DaughterHalf Life (yrs)Range (yrs) 238 U/ 206 Pb 14 C 3 H/ 3 He 4.5 billion 5730 12.3 10 million to 4.5 billion 100 to 70,000 1 to 50
Parent/Daughter 238 U/ 206 Pb 14 C 3 H/ 3 He Material Dated Igneous and Metamorphic rocks Organic material Water
Uranium (U) - Thorium (Th) - Lead (Pb) 238U decays to 206Pb (4.5 billion) 235U decays to 207Pb (713 million) 232Th decays to 208Pb (14.1 billion) >Rocks containing Uranium provide three possible techniques. >Because all three occur together, it allows a method to cross-check the dates. >Uses zircons, uraninite and uranium ores
Potassium (K) - Argon (Ar) Dating >Potassium (K) is an extremely common element. >Half-life (t1/2) is 1.3 billion years. >Range is 100,000 to 4.6 billion years. >Useful for relatively young and very old rocks. >Found in muscovite, biotite, orthoclase and glauconite. >Used to date volcanic rocks.
Carbon 14 / Carbon 12 >Cosmic rays hit Nitrogen 14 changing it to Carbon 14. >Carbon 14 is taken in by organisms. >When organism dies, amount of C-14 decreases.
Dating techniques that can be used on this geologic column: absolute dating paleomagnetism superposition fossil correlation
What is the Parent / Daughter ratio of a sample of radiogenic material if the original sample was 200g. and 3 half-lifes have passed. If the half-life is 20,000 years, how old is the sample? What is the half-life of an isotopic pair if the sample is 2 million years old and contains 625g of parent and 9375g of daughter isotope?