What is annihilation in terms of nuclear processes? Also, what are transuranium elements and how are they synthesized? Scientists have estimated that the earth's crust was formed 4.3 billion years ago. The radioactive nuclide 176Lu, which decays to 176Hf, was used to estimate this age. The half-life of 176Lu is 37 billion years. How are ratios of 176Lu to 176Hf utilized to date very old rocks?