Carbon Dating Earth’s Past

By Ed Martinez

October 14, 2008

Archeology is a field of study that has been revolutionized by the introduction of carbon dating. The process was developed by Professor Willard Libby at the University of Chicago in 1949. This finding led to worldwide recognition when he was awarded the Nobel Prize in Chemistry in 1960. Since its discovery, it has been the focus of controversy. Is it really a valid process for determining the age of organic materials?  The answer is yes and no. To fully understand the process, it is important to learn how it works, and understand what materials cannot be carbon-dated and why.

Carbon dating can be performed on any material found on Earth, which received carbon from the air in the last 50,000 years. The carbon is produced from the upper atmosphere by the radiation from the sun. Organic materials such as land plants and animals can be carbon-dated, since they receive their carbon from carbon dioxide in the air. Carbon has three naturally occurring isotopes. They are C-12, C-13 and C-14. C-14 in an unstable and radioactive isotope, which decays into Nitrogen-14 through the loss of an electron, also known as beta decay. Both C-12 and C-13 are stable isotopes and do not decay. After an organism dies, the carbon C-14 continues to decay without being replaced. To measure the amount of radiocarbon left, scientists extract a small piece of the material and burn it, which converts it into carbon dioxide gas. Radiation counters are then used to detect the electrons given off by C-14 as it turns into Nitrogen-14. The amount of C-14 is then compared to the amount of the stable C-12 to determine how much radiocarbon has decayed, which yields a date.

What are some of the problems with carbon dating?  There are two main issues at the center of controversy. One has to do with the contamination of target samples with modern or other carbon sources. There is also the assumption that the amount of C-14 in the atmosphere has always remained consistent. Some scientists believe that the C-14 production in the atmosphere has not been constant throughout Earth’s existence and can lead to variations of C-14 on materials. They estimate that the amounts of C-14 in the atmosphere have decreased over the past 10,000 years and can also experience fluctuations from time-to-time. The decrease in the Earth’s geomagnetic field may be to blame for the fluctuations of C-14 levels. If these issues are not taken into account, the carbon dating process becomes unreliable.  

Aquatic creatures cannot be carbon-dated since the carbon they breathe comes from the sea. What about dinosaur fossils?  Many believe that dinosaur fossils can be carbon-dated. The reality is that they cannot. They are usually too old and rarely contain any of the original carbon. The age of a dinosaur fossil is estimated by analyzing the volcanic rock beneath the fossil, which predates the fossil, and above the fossil, which represents a time after the dinosaur’s existence. This results in a time-range for the dinosaur’s life.

The carbon-dating process when applied to recent archeological artifacts has performed well. When compared to historical records, accurate dates have been provided for items such as Egyptian objects and the Dead Sea Scrolls, just to name a couple.