What is radioactive dating
He noted that different formations contained different fossils and he could map one formation from another by the differences in the fossils.As he mapped across southern England, he drew up a stratigraphic succession of rocks although they appeared in different places at different levels.
("87" is the atomic mass number = protons neutrons.Accurate radiometric dating generally requires that the parent has a long enough half-life that it will be present in significant amounts at the time of measurement (except as described below under "Dating with short-lived extinct radionuclides"), the half-life of the parent is accurately known, and enough of the daughter product is produced to be accurately measured and distinguished from the initial amount of the daughter present in the material.The procedures used to isolate and analyze the parent and daughter nuclides must be precise and accurate.Over hundreds to thousands of millions of years, continents, oceans and mountain ranges have moved vast distances both vertically and horizontally.For example, areas that were once deep oceans hundreds of millions of years ago are now mountainous desert regions.Fossil assemblages 'fingerprint' formations, even though some species may range through several different formations.
This feature allowed William Smith (an engineer and surveyor who worked in the coal mines of England in the late 1700s) to order the fossils he started to collect in south-eastern England in 1793.
After Charles Darwin's publication Origin of Species (Darwin himself was also a geologist) in 1859, geologists realised that particular fossils were restricted to particular layers of rock.
This built up the first generalised geological time scale.
For instance, carbon-14 has a half-life of 5,730 years.
After an organism has been dead for 60,000 years, so little carbon-14 is left that accurate dating can not be established.
It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of alteration. Precision is enhanced if measurements are taken on multiple samples from different locations of the rock body.