ASBOG Practice Exam

Rubidium-strontium isotope dating is a technique primarily used for:

1. Dating living organisms

2. Whole rock dating of sedimentary materials

3. Whole rock dating of igneous materials over 10 million years old

4. Dating fossils in sedimentary rocks

The correct answer is: Whole rock dating of igneous materials over 10 million years old

Rubidium-strontium isotope dating is particularly useful for whole rock dating of igneous materials, especially those that are over 10 million years old. This technique relies on the decay of rubidium-87 to strontium-87, with a half-life of about 50 billion years, making it suitable for dating geological events over extensive time scales such as the formation of igneous rocks. In igneous rocks, the closed system behavior of the rubidium-strontium isotope pair enables geologists to accurately calculate the age of the rock formation, as the strontium isotopes can give insights into the time of crystallization from the molten state. This contrasts with other dating methods that are less effective for older terrestrial materials. The method is not typically used for dating living organisms or fossils, which require different approaches due to the distinct processes governing their decay and formation. Similarly, while it can be applied to sedimentary materials, the isotopic ratios can be complicated by factors such as source material mixing and the potential for resetting isotopic signatures during metamorphic events. Therefore, its primary application remains centered on igneous rocks, particularly those significantly older than 10 million years.