A fossil will always be younger than fossils in the beds beneath it and this is called the principle of superposition.
In an undisturbed sequence of rocks, such as in a cliff face, it is easy to get a rough idea of the ages of the individual strata – the oldest lies at the bottom and the youngest lies at the top.
The only way that this can happen is by changing the number of protons in the nucleus (an element is defined by its number of protons).
There are a number of ways that this can happen and when it does, the atom is forever changed.
When atoms decay, they emit three types of radiation, alpha, beta and gamma.
Radioactive decay involves the spontaneous transformation of one element into another.Protons and neutrons together are called nucleons, meaning particles that can appear in the atomic nucleus.A nuclide of an element, also called an isotope of an element, is an atom of that element that has a specific number of nucleons.Alpha particles are most commonly used in smoke alarms.These alarms contain a tiny amount of decaying Americium between two sheets of metal. A small electric current is then passed through one of the sheets and into the second one.There is no going back – the process is irreversible. When we pour our popcorn kernels into a popcorn popper, the is no way to know which will pop first.And once that first kernel pops, it will never be a kernel again..is forever changed! ) Teaching example using popcorn to teach radioactive decay "A variety of a chemical element (strictly, of one particular element) which is distinguished from the other varieties of the element by a different mass number but shares the same atomic number and chemical properties (and so occupies the same position in the periodic table)." That definition may not mean anything to them.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.Sometimes, scientists already know the age of the fossil because fossils of the same species have been found elsewhere and it has been possible to establish accurately from those when the dinosaur lived.Geologists call this the principle of lateral continuity.