The currently accepted calculation of the solar system’s age is derived from comparing lead-206, a daughter isotope of uranium-238, to lead-207, a daughter isotope of uranium-235.
That comparison relies on knowing the ratio of uranium-238 to uranium-235. Earlier calculations of the ratio all came up with the same number, 137.88. The assumption that the ratio was constant simplified calculations greatly — it allowed scientists to combine both uranium values into a single number, eliminating one variable from the equation. Lead isotopes are easier to measure with high precision than uranium isotopes, so an age-estimation system based only on lead values was thought to be extremely precise.
“Everybody was sitting on this two-legged stool claiming it was very stable,” comments Gerald Wasserburg, emeritus professor of geology at Caltech who was involved in much of the early work in measuring uranium ratios. “But it turns out it’s not.”
Tuesday, January 12, 2010
Age of the Solar System Needs Recalculating
From Wired.