Radioactive decay dating can be used for which rock types?

Radioactive decay dating can be used for which rock types?

• A. Igneous and metamorphic rocks only
• B. Sedimentary rocks only
• C. All rock types
• D. Metamorphic rocks only

Answer: (A)

Radioactive decay dating depends on a mineral’s isotopic clock starting when that mineral crystallizes or forms, and it can only stay reliable if the system remains closed to parent and daughter isotopes. Igneous rocks are ideal because they crystallize from molten material in a single event, so the minerals selected for dating capture a clear start time for the clock. Metamorphic rocks can also yield radiometric ages, because minerals may grow or reset their clocks during metamorphism, and certain minerals (like zircon) can preserve that time signal, though interpreting ages can be more complex if multiple events occurred. Sedimentary rocks, by contrast, are assembled from grains produced earlier by others, so dating the rock as a whole would rather reveal the ages of the source materials or later diagenetic events, not the time of deposition. Because of this, radiometric dating is used for igneous rocks and, in some metamorphic minerals, for metamorphic rocks as well.

Radioactive decay dating depends on a mineral’s isotopic clock starting when that mineral crystallizes or forms, and it can only stay reliable if the system remains closed to parent and daughter isotopes. Igneous rocks are ideal because they crystallize from molten material in a single event, so the minerals selected for dating capture a clear start time for the clock. Metamorphic rocks can also yield radiometric ages, because minerals may grow or reset their clocks during metamorphism, and certain minerals (like zircon) can preserve that time signal, though interpreting ages can be more complex if multiple events occurred. Sedimentary rocks, by contrast, are assembled from grains produced earlier by others, so dating the rock as a whole would rather reveal the ages of the source materials or later diagenetic events, not the time of deposition. Because of this, radiometric dating is used for igneous rocks and, in some metamorphic minerals, for metamorphic rocks as well.