The half-life of a radioactive nuclide is defined as the time it takes half of a sample of the element to decay.

A mathematical formula can be used to calculate the half-life from the number of breakdowns per second in a sample of the nuclide. Some, however, are unstable -- given time, they will spontaneously undergo one of the several kinds of radioactive decay, changing in the process into another element.

There are two common kinds of radioactive decay, alpha decay and beta decay.

Some nuclides have very long half-lives, measured in billions or even trillions of years.

Others have extremely short half-lives, measured in tenths or hundredths of a second.

Radiometric dating methods are the strongest direct evidence that geologists have for the age of the Earth.

All these methods point to Earth being very, very old -- several billions of years old.In alpha decay, the radioactive atom emits an alpha particle.An alpha particle contains two protons and two neutrons.Thats the essence of radiometric dating: measure the amount thats present, calculate how much is missing, and Obviously, the major question here is "how much of the nuclide was originally present in our sample? If an element has more than one nuclide present, and a mineral forms in a magma melt that includes that element, the elements different nuclides will appear in the mineral in precisely the same ratio that they occurred in the environment where and when the mineral was formed. The third and final axiom is that when an atom undergoes radioactive decay, its internal structure and also its chemical behavior change.Losing or gaining atomic number puts the atom in a different row of the periodic table, and elements in different rows behave in different ways. C14 is radioactive, with a half-life of 5730 years.Protons and neutrons together are called nucleons, meaning particles that can appear in the atomic nucleus.

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