The universe is full of naturally occurring radioactive elements.Radioactive atoms are inherently unstable; over time, radioactive "parent atoms" decay into stable "daughter atoms." When molten rock cools, forming what are called igneous rocks, radioactive atoms are trapped inside. By measuring the quantity of unstable atoms left in a rock and comparing it to the quantity of stable daughter atoms in the rock, scientists can estimate the amount of time that has passed since that rock formed.This is despite the fact that it causes more problems for interpreting rock strata than it solves.
Steve Austin and his associates at the Institute for Creation 'Research' (ICR) collected a dacite sample from Mt. Helens, Washington State, USA, which probably erupted in 1986 AD. then ineffectively separated the sample into several mineral and glass 'fractions', submitted the dacite and its 'fractions' for potassium 40-argon 40 (K-Ar) dating, and subsequently used the bogus results to inappropriately attack the K-Ar method.
So in order to date most older fossils, scientists look for layers of igneous rock or volcanic ash above and below the fossil.
Scientists date igneous rock using elements that are slow to decay, such as uranium and potassium.
It caused massive sedimentary layering and sorting and fossilizing of the creatures buried therein.
Most scientists today believe that life has existed on the earth for billions of years.