The most widely known form of radiometric dating is carbon-14 dating.This is what archaeologists use to determine the age of human-made artifacts. The half-life of carbon-14 is only 5,730 years, so carbon-14 dating is only effective on samples that are less than 50,000 years old.Strata Thickness- In the late 1800s, a British geologist estimated that 75 million years has lapsed since the beginning of the Cambrian.This estimate was based upon the maximum known thickness of strata (from Cambrian to present) divided by the average rate of sedimentation in modern environments. Joly used the salinity of ocean water to determine the age of the earth.Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.
In the 1860's, English physicist Lord Kelvin disagreed with Charles Lyells proposition that the earth behaves in a uniform, unchanging manner.
But this sediment doesn't typically include the necessary isotopes in measurable amounts.
Fossils can't form in the igneous rock that usually does contain the isotopes.
Some of the isotopes used for this purpose are uranium-238, uranium-235 and potassium-40, each of which has a half-life of more than a million years.
Unfortunately, these elements don't exist in dinosaur fossils themselves.