U.S. Geological Survey
Earth Surface Processes

Amino Acid Dating

Amino acids are the building blocks of protein. There are many different types and shapes, and it's the shapes that make some amino acids good dating tools. The amino acids, leucine and isoleucine, have one orientation while they are in a living organism, but flip over to a different orientation after that organism dies. Mollusks, like snails and clams, are often analyzed this way using the amino acids D/L aspartic acid and D/L leucine.

Time and temperature affect the ratio of flipped to unflipped amino acids. These effects have been determined (more or less) from many studies of fossils of known age. By measuring the ratio of flipped to unflipped amino acids, we can estimate how much time has passed. We use a process called high pressure liquid chromatography to "see" the amino acid orientation. Darrell Kaufman has analyzed many of the sediments from Bear Lake and the surrounding area. Ben Laabs is also working at Bear Lake, using amino acids and tephrochronology (the use of volcanic ashes for dating) to date the high shorelines, looking for possible geomorphic or tectonic causes of the highest lake stands. Laabs is an MS Geology student at Northern Arizona University. Preliminary results indicate the technique is useful for establishing when Bear Lake was high in the past million years.

To learn more about amino acid racemization uses in geology, visit these sites:

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