All these methods point to Earth being very, very old -- several billions of years old.
For example, hydrogen-1 and hydrogen-2 are both nuclides of the element hydrogen, but hydrogen-1's nucleus contains only a proton, while hydrogen-2's nucleus contains a proton and a neutron.
Uranium-238 contains 92 protons and 146 neutrons, while uranium-235 contains 92 protons and 143 neutrons.
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.
These layers are like bookends -- they give a beginning and an end to the period of time when the sedimentary rock formed.
By using radiometric dating to determine the age of igneous brackets, researchers can accurately determine the age of the sedimentary layers between them.
For example, by using a laser, researchers can measure parent and daughter atoms in extremely small amounts of matter, making it possible to determine the age of very small samples [source: New Scientist].
Radiometric dating methods are the strongest direct evidence that geologists have for the age of the Earth.
To keep it short, a nuclide is usually written using the elements abbreviation.
Uraniums abbreviation is U, so uranium-238 can be more briefly written as U238.
You can learn more about fossils, dinosaurs, radiometric dating and related topics by reading through the links on the next page.