determination of the age of fossil -radioactive

Question

DETERMINATION OF THE AGE OF FOSSIL -

1. Radioactive clock (Boltwood-1907) - Half life of uranium is 4.5 billion years.
2. This means half of total uranium disintegrates into lead in 4.5 billion years 235u decays to 206pb. By calculating the amount of lead in a rock, one can approximately estimate the age of fossil.
3. Radio carbon method - (W.E Libby - 1950).
4. Potassium argon method - Potassium is a common element found in al rocks.