Carbon cycle used dating artifacts
After showing the essential uniformity of carbon-14 in living material, Libby sought to answer the second question by measuring the radiocarbon level in organic samples dated historically—materials as old as 5,000 years from sources such as Egyptian tombs.
With correction for radioactive decay during the intervening years, such old samples hopefully would show the same starting carbon-14 level as exists today. His conclusion was that over the past 5,000 years the carbon-14 level in living materials has remained constant within the 5 percent precision of measurement.
Radioactive carbon thus was visualized as gaining entrance wherever atmospheric carbon dioxide enters—into land plants by photosynthesis, into animals that feed on the plants, into marine and fresh waters as a dissolved component, and from there into aquatic plants and animals.
In short, all parts of the carbon cycle were seen to be invaded by the isotope carbon-14.
A dating method was thus available, subject only to confirmation by actual application to specific chronologic problems.
Since Libby’s foundational studies, tens of thousands of carbon-14 measurements of natural materials have been made.
In every case, the living material affected gives the appearance of built-in age.
Specifically, volcanic carbon dioxide is known to depress the carbon-14 level of nearby vegetation, and dissolved limestone carbonate occasionally has a similar effect on freshwater mollusks, as does upwelling of deep ocean water on marine mollusks.Expressed as a fraction of the contemporary level, they have been mathematically converted to ages through Improvements in measurement accuracy and the ever-mounting experience in applying carbon-14 dating have provided superior and more voluminous data with which to better answer Libby’s original questions.It is now clear that carbon-14 is not homogeneously distributed among today’s plants and animals.Carbon-14 dating is a way of determining the age of certain archeological artifacts of a biological origin up to about 50,000 years old.It is used in dating things such as bone, cloth, wood and plant fibers that were created in the relatively recent past by human activities.