Presentation on theme: "Radioactive Dating D.3.1 Outline the method for dating rocks and fossils using radioisotopes, with reference to 14 C and 40 K."— Presentation transcript:
Radioactive Dating D.3.1 Outline the method for dating rocks and fossils using radioisotopes, with reference to 14 C and 40 K.
D.3.1 Outline the method for dating rocks and fossils using radioisotopes, with reference to 14 C and 40 K. 14 C is a naturally occurring isotope of carbon with a half life of 5730 years; It is constantly being made in the atmosphere when cosmic rays cause neutrons to fuse with nitrogen nuclei and kick out protons 14 C production is in equilibrium with its decay to 12 C The 14 C is incorporated in carbon dioxide which is then taken up by plants. In the end all living things have the same ratio of 14 C to 12 C When an organism dies it no longer takes in 14 C. So over time the ratio of 14 C to 12 C changes. This is measurable and can be used to estimate age. *The limit for accurate determination of age is about 50,000yrs* Formation Decay
40 K is an isotope with a half life of 1.3 X 10 9 yrs It decays to 40 Ar. When 40 K is released from a volcano in lava all of the argon gas is driven off. So brand new rocks effectively have a ratio 40 K: 40 Ar (or 100:0) Over time the lava may be weathered and eroded and incorporated into sedimentary rocks. *The measured ratio of 40 K to 40 Ar can be used to date rocks over one million years old with an accuracy of around 50,000 years*
D.3.2 Define half-life. Simulation of many identical atoms undergoing radioactive decay, starting with either four atoms (left) or 400 atoms (right). The number at the top indicates how many half-lives have elapsed The time it takes for half of a radioactive isotope to decay
What is the half life for each of the isotopes represented by these curves?
D.3.3 Deduce the approximate age of materials based on a simple decay curve for a radioisotope. Play the game