Relative Dating

Radiometric dating - Wikipedia

Quantum electronics to Reasoning. The discovery of the radioactive properties of uranium in by Henri Becquerel subsequently revolutionized the way scientists measured the age of artifacts and supported the theory that the earth was considerably older than what some scientists believed.


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There are several methods of determining the actual or relative age of the earth's crust: However, one of the most widely used and accepted method is radioactive dating. All radioactive dating is based on the fact that a radioactive substance, through its characteristic disintegration, eventually transmutes into a stable nuclide.

Radioactive Decay

When the rate of decay of a radioactive substance is known, the age of a specimen can be determined from the relative proportions of the remaining radioactive material and the product of its decay. In , the American chemist Bertram Boltwood demonstrated that he could determine the age of a rock containing uranium and thereby proved to the scientific community that radioactive dating was a reliable method.

Radioactive Dating

Uranium, whose half-life is 4. Boltwood explained that by studying a rock containing uranium, one can determine the age of the rock by measuring the remaining amount of uranium and the relative amount of lead The more lead the rock contains, the older it is. The long half-life of uranium makes it possible to date only the oldest rocks.

This method is not reliable for measuring the age of rocks less than 10 million years old because so little of the uranium will have decayed within that period of time. This method is also very limited because uranium is not found in every old rock.

Radioactive Dating

It is rarely found in sedimentary or metamorphic rocks, and is not found in all igneous rocks. Although the half-life of rubidium is even longer than uranium 49 billion years or 10 times the age of the earth , it is useful because it can be found in almost all igneous rocks.

Radioactive Dating of Fossils

Potassium is a very common mineral and is found in sedimentary, metamorphic, and igneous rock. Also, the half-life of potassium is only 1.


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  4. In , a radioactive dating method for determining the age of organic materials, was developed by Willard Frank Libby, who received the Nobel Prize in Chemistry in for his radiocarbon research. All living plants and animals contain carbon , and while most of the total carbon is carbon, a very small amount of the total carbon is radioactive carbon Libby found that the amount of carbon remains constant in a living plant or animal and is in equilibrium with the environment, however once the organism dies, the carbon within it diminishes according to its rate of decay.

    This is because living organisms utilize carbon from the environment for metabolism. Libby, and his team of researchers, measured the amount of carbon in a piece of acacia wood from an Egyptian tomb dating B. Atoms may have an equal number of protons and neutrons. If, however, there are too many or too few neutrons, the atom is unstable, and it sheds particles until its nucleus reaches a stable state.

    Think of the nucleus as a pyramid of building blocks. If you try to add extra blocks to the sides pyramid, they may stay put for a while, but they'll eventually fall away. The same is true if you take a block away from one of the pyramid's sides, making the rest unstable. Eventually, some of the blocks can fall away, leaving a smaller, more stable structure. The result is like a radioactive clock that ticks away as unstable isotopes decay into stable ones. You can't predict when a specific unstable atom, or parent , will decay into a stable atom, or daughter.

    But you can predict how long it will take a large group of atoms to decay. The element's half-life is the amount of time it takes for half the parent atoms in a sample to become daughters.

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    To read the time on this radioactive clock, scientists use a device called a mass spectrometer to measure the number of parent and daughter atoms. The ratio of parents to daughters can tell the researcher how old the specimen is.

    The more parent isotopes there are -- and the fewer daughter isotopes -- the younger the sample. The half-life of the isotope being measured determines how useful it is at dating very old samples.