Question

how would a geologist use absolute dating to determine the age of sedimentary layers?
by dating the age of several radioactive elements in a sedimentary rock layer
by dating the age of intrusions and extrusions near a sedimentary rock layer
by comparing the relative ages of several sedimentary rock layers
by identifying fossils in nearby intrusion and extrusions and determining their age

Explanation:

Sedimentary rocks are formed from sediments. Absolute dating is often done using radioactive elements. However, sedimentary rocks usually have multiple sources of sediments, so the radioactive elements in them may not accurately represent the age of the sedimentary layer. Intrusions (igneous rocks that form below the surface) and extrusions (igneous rocks that form on the surface) near sedimentary layers can be dated using absolute dating methods (like radiometric dating). Since intrusions and extrusions cut through or are adjacent to sedimentary layers, their ages can help determine the age range of the sedimentary layers. For example, if an intrusion is younger than a sedimentary layer (because it cuts through it), and an extrusion is older than another sedimentary layer (because the sedimentary layer forms on top of it), this gives a time frame for the sedimentary layers.

• Option 1: Sedimentary rocks are made of sediments from various sources. Radioactive elements in them may not be from the same time of sedimentary layer formation, so dating them is not reliable for the age of the sedimentary layer.
• Option 3: Comparing relative ages is relative dating, not absolute dating.
• Option 4: Identifying fossils is more related to relative dating (using index fossils) rather than absolute dating for the purpose in the question.

Answer:

by dating the age of intrusions and extrusions near a sedimentary rock layer