ASBOG Practice Exam

Which dating method would best be used for rocks dating back over 4 billion years?

1. Carbon-14 dating

2. Uranium-lead isotopes

3. Rubidium-strontium dating

4. Potassium-argon dating

The correct answer is: Uranium-lead isotopes

The most suitable dating method for rocks that are over 4 billion years old is uranium-lead isotopes. This technique utilizes the decay of uranium isotopes into lead isotopes, providing a reliable means of dating ancient geological samples. Uranium has a relatively long half-life, with the isotopes U-238 and U-235 decaying over billions of years, making it ideal for dating the oldest rocks on Earth. This method not only allows for dating very old samples but also offers distinct advantages in terms of precision and accuracy. By comparing the ratios of uranium and lead isotopes within a sample, geologists can determine when the rock first formed, which is critical for understanding the geological history of the Earth. Other methods such as carbon-14 dating are not suitable for dating ancient rocks because carbon-14 has a much shorter half-life of about 5,730 years, making it effective only for dating materials that are up to about 50,000 years old, such as organic remains. Rubidium-strontium dating, while useful for some geological materials, typically applies to slightly younger rocks with ages in the range of millions of years rather than billions. Potassium-argon dating also has its limitations and is generally used for younger geological formations,