Why isn’t the radiometric dating of sedimentary rock exact?

Question

Because sedimentary rock only forms where there were ancient seas.

Because sedimentary rock is made up of weathered and eroded bits of igneous rock.

Because sedimentary rock is constructed of many different layers.

Because sedimentary rock only contains carbon-14 and no other radioactive isotopes.

Answer 1

The most accurate reason why radiometric dating of sedimentary rock is not precise is:

Because sedimentary rock is constructed of many different layers.

Sedimentary rocks are formed from the accumulation of sediments that can originate from various sources and may vary in age. The individual grains of sediment may have been deposited at different times, making it challenging to assign a single age to the entire rock layer. In contrast, igneous rocks can often be dated more accurately because they generally crystallize from a molten state created at a specific time. Radiometric dating of sedimentary rocks often involves dating the enclosing igneous or metamorphic rocks or dating the fossils within the sedimentary layers, rather than the sedimentary rock itself.