Absolute and relative dating examples

The radioactive carbon-14 method of dating is used to determine the age of organic matter that is several hundred years to approximately 50,000 years old.

Carbon dating is possible because all organic matter, including bones and other hard parts, contains carbon and thus contains a scalable proportion of carbon-14 to its decay product, nitrogen-14.

By matching the tree rings on an archaeological sample to the master sequence of tree ring patterns, the absolute age of a sample is established.The best known dendrochronological sequences are those of the American Southwest, where wood is preserved by aridity, and Central Europe, where wood is often preserved by waterlogging.When archaeologists have access to the historical records of civilizations that had calendars and counted and recorded the passage of years, the actual age of the archaeological material may be ascertained—provided there is some basis for correlating our modern calendar with the ancient calendar.With the decipherment of the Egyptian hieroglyphics, Egyptologists had access to such an absolute timescale, and the age, in calender years, of the Egyptian dynasties could be established.Those laid down during the fall and winter have a dark color because of the presence of dead vegetation; those deposited during the rest of the year have a light color.

The stratigraphy may also reflect seasonal variation in the velocity of stream flow.Since the rate of radioactive decay of any particular isotope is known, the age of a specimen can be computed from the relative proportions of the remaining radioactive material and its decay products.By this method the age of the earth is estimated to be about 4.5 billion years old.In dendrochronology, the age of wood can be determined through the counting of the number of annual rings in its cross section.Tree ring growth reflects the rainfall conditions that prevailed during the years of the tree's life.The carbon-14, along with nonradioactive carbon-13 and carbon-12, is converted to carbon dioxide and assimilated by plants and organisms; when the plant or animal dies, it no longer acquires carbon, and the carbon-14 begins to decay.