Although Boltwood's resulting estimates for things like the age of Earthwhich he placed at around 2.2 billion yearshave since been significantly revised, he indicated correctly that our planet was far older than people had imagined possible.
Although the time at which any individual atom will decay cannot be forecast, the time in which any given percentage of a sample will decay can be calculated to varying degrees of accuracy.
The time that it takes for half of a sample to decay is known as the half life of the isotope.
Carbon, uranium and potassium are just a few examples of elements used in radioactive dating.
Each element is made up of atoms, and within each atom is a central particle called a nucleus.
Some isotopes have half lives longer than the present age of the universe, but they are still subject to the same laws of quantum physics and will eventually decay, even if doing so at a time when all remaining atoms in the universe are separated by astronomical distances.
Various elements are used for dating different time periods; ones with relatively short half-lives like carbon-14 (or C) are useful for dating once-living objects (since they include atmospheric carbon from when they were alive) from about ten to fifty thousand years old. Longer-lived isotopes provide dating information for much older times.
Within the nucleus, we find neutrons and protons; but for now, let's just focus on the neutrons.
These neutrons can become unstable, and when they do, they release energy and undergo decay. Radioactivity occurs when the nucleus contains an excess amount of neutrons.
Historical geologists are scientists who study the Earth's past.
They study clues left on the Earth to learn two main things: the order in which events happened on Earth, and how long it took for those events to happen.
When an atom varies in the number of neutrons, the variation is called an isotope. During radioactivity, the unstable isotope breaks down and changes into a different substance.