... Pb 204 Pb � = 4.46 (1. 36) 16 CHAPTER THE EARTH IN THE SOLAR SYSTEM The age information is contained in the slope, M , using only isotopes of Pb The value of 235 U/238 U is 1/ 137.88, and this ratio ... (1. 1) in terms of the mass of the sun and doing so yields L = mr2 ω = (GMs )1/ 2 mr1/2 (1. 6) By integrating (1. 6) over all the planets we find that while the sun contains 99.8% of the mass of the ... be estimated CHAPTER THE EARTH IN THE SOLAR SYSTEM 14 1. 7 Radiometric Dating The Rubidium-Strontium System To illustrate the radiometric dating technique, consider the decay of the unstable isotope...