How would i go about finding this?

The 235U/238U ratio is more or less uniform in all materials. However, given the different rates of decay of the two isotopes, the ratio would have been different when the Earth formed. Calculate the 235U/238U for when the Earth formed at 4.567 Ga. Use 235U/238U = 1/137.88 as the present day ratio. The 235U/238U ratio is more or less uniform in all materials. However, given the different rates of decay of the two isotopes, the ratio would have been different when the Earth formed. Calculate the 235U/238U for when the Earth formed at 4.567 Ga. Use 235U/238U = 1/137.88 as the present day ratio