The radiometric dater then uses the half-life of all four isotopes to find an age range the rock should be in.The half-lives of the cascade from uranium-235 to lead-207 has been been extrapolated to about 704 million years and the cascade form uranium-238 to lead-206 has been calculated to about 4.47 billion years.Unlike any other method, uranium-lead has a natural cross-check built into it that shows when nature has tampered with the evidence.Uranium comes in two common isotopes with atomic weights of 235 and 238 (we'll call them 235U and 238U).This would be the estimated age of the earliest life or fossils. Uranium 238 is only found igneous or volcanic rocks. Because of the huge differences in the half lives of Carbon 14 and Uranium238 that cannot be used together.Carbon 14 can only be used to date fossils of a very recent age.Due to this reason it has been denoted by an Alpha particle in the second reaction.Thorium-234 is the next radioactive substance in the decay process of Uranium-238.
The process of dating finds the two ratios between uranium-235 and lead-207; and uranium-238 and lead-206.
The amount of carbon-14 in the atmosphere has not changed in thousands of years.
Even though it decays into nitrogen, new carbon-14 is always being formed when cosmic rays hit atoms high in the atmosphere.
By comparing how much carbon-14 there is in the dead organism with the amount in a living one, the age of the dead organism can be estimated.
The half-life of uranium-238 is 4500 million years.