11. Use equations (9.15), (9.22) and(9.23) to construct a concordia diagram for 3500 Ma of Earthhistory. Begin with 1000 atoms each of 235U and238U at an initial time of 0 years, and increment timein 200 Ma increments, calculating N (the number of atoms remaining)and D* (the number of daughter isotopes = No-N) for bothdecay schemes at each increment. Then plot207Pb/235U vs.206Pb/238U to construct a concordiadiagram.
Once you have a diagram, add thefollowing points as a discordia:You can add the points in Excel bycopying them, selecting the chart, and using Paste-Special as a newseries. Draw a best-fit line through the discordia points andestimate the initial crystallization age and the metamorphicage.
207Pb/235U | 206Pb/238U |
5 | 0.240 |
10 | 0.355 |
12 | 0.400 |
15 | 0.470 |
17 | 0.520 |
19 | 0.560 |
