Question

how is radioactive decay used to date sedimentary rocks?
the amounts of potassium and argon in sedimentary rocks are measured.
the amounts of carbon-14 and nitrogen in sedimentary rocks are measured.
the amounts of unstable elements in each layer of the sedimentary rocks are compared.
the amounts of unstable elements in the volcanic layers above and below the sedimentary layers are measured.

Explanation:

To date sedimentary rocks using radioactive decay, we analyze the options:

• Potassium - argon dating is for igneous rocks, not sedimentary, so the first option is wrong.
• Carbon - 14 dating is for organic materials, not sedimentary rocks, so the second option is wrong.
• Just measuring unstable elements in sedimentary layers doesn't work as sedimentary rocks have particles from various sources.
• Sedimentary rocks are between volcanic (igneous) layers. By measuring unstable elements (like in potassium - argon or other radiometric methods) in the volcanic layers above and below the sedimentary layers, we can date the sedimentary rocks as they were deposited between the formation of these volcanic layers.

Answer:

The amounts of unstable elements in the volcanic layers above and below the sedimentary layers are measured.