The ages of rocks that contain fossils can be determined using the isotope 87rb. this isotope of rubidium undergoes beta decay with a half‑life of 4.75×1010y . ancient samples contain a ratio of 87sr to rb87 of 0.0165. given that 87sr is a stable product of the beta decay of 87rb, and assuming there was originally no 87sr present in the rocks, calculate the age of the rock sample. assume that the decay rate is constant over the relatively short lifetime of the rock compared to the half-life of 87rb.