ASBOG Practice Exam

Uranium-lead isotopes are effective for dating what type of materials?

1. Geologic materials between 1 million and 4.5 billion years old

2. Organic materials less than 50,000 years old

3. Soil deposits

4. Metamorphic rocks younger than 100,000 years

The correct answer is: Geologic materials between 1 million and 4.5 billion years old

Uranium-lead isotopes are highly effective for dating geological materials that are between 1 million and 4.5 billion years old due to the long half-lives of the isotopes involved. The uranium-lead dating method utilizes two different decay chains: uranium-238 decays to lead-206, and uranium-235 decays to lead-207. This dual approach allows for cross-checking results and helps provide precise age estimates, especially for minerals like zircon, which often occur in igneous and metamorphic rocks. The capability of uranium-lead dating extends back to some of the oldest rocks known on Earth, making it particularly suited for dating ancient geological formations. The precision and range of this method make it an essential tool for geologists studying early Earth history and the formation of the planet. In contrast, the other options pertain to materials that are either too young or do not present the suitable conditions for uranium-lead dating, as organic materials and soil deposits typically require other dating methods, such as radiocarbon dating or luminescence techniques.