ASBOG Practice Exam

Potassium-argon dating is primarily used for which of the following?

1. Organic materials under 10,000 years

2. Geologic materials greater than 100,000 years in age

3. Soil layers less than 1,000 years old

4. Fossils from early life forms

The correct answer is: Geologic materials greater than 100,000 years in age

Potassium-argon dating is a radiometric dating method used primarily to determine the age of geological materials over a time span that typically exceeds 100,000 years. This method relies on the radioactive decay of potassium-40 to argon-40, which allows geologists to date volcanic rocks and ash layers that are millions of years old. Since potassium-40 has a relatively long half-life of about 1.25 billion years, it is particularly effective for dating ancient geological formations. This makes it advantageous for studying the age of the Earth’s crust and significant geological events, as isotopic ratios can provide accurate dates for volcanic eruptions and sedimentation periods that occurred well before recorded human history. In contrast, the other options are less suitable for potassium-argon dating. For example, organic materials (like bones or wood) that are under 10,000 years old can be more accurately dated with methods such as carbon-14 dating. Soil layers that are less than 1,000 years old also fall beneath the effective range for potassium-argon dating, while fossils, particularly from early life forms, are better dated using other techniques that can target the age of the sedimentary rock layers in which they are found. Thus, the application of