Samarium-Neodymium Dating Method

by Danielle Ketrow

Submitted : Spring 2015

Geologic surveys attempt to create a picture of how the structures seen on earth today were formed. An important factor in this is of course not only finding the composition of the structures, but also the age. Several clues can be used to determine the age of rocks including sedimentary deposits and fossil records. However, a more accurate dating method is radiometric dating. Radiometric dating uses the ratio of a known radioactive material to its daughter isotope and compares it to the ratios of newly formed rocks. By using the decay constant, this ratio can be used to find the age of the rock in question. The Watersmeet Gneiss Dome in Northern Michigan was recently surveyed and data regarding the radioisotope samarium 147 was recorded. Using the data found of the ratios of samarium 147 and its daughter isotope, neodymium 143, the age of this geologic structure was found to be between 1.99 and 3.71 billion years old. Older data places the formation of this entire structure in the Archaen age, however this study contradicts that timeline. While the majority of the structure was formed in that age, other parts are newer, and can fall into the Proterozoic age, meaning that this geologic structure was formed over a longer period of time, that extended into the more recent past than previously expected.

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