1.
a. Radioactive decay is the process in which elements break down by releasing particles.
b. A composition of rock containing a radioactive element change over time because over a period of time they decay, and during this process the atoms of the element break down to form atoms of another element.
c.
2.
a. Geologist use radioactive dating to determine the absolute age of a rock.
b. It is very difficult to determine the absolute age of a sedimentary rock because the rock particles in a sedimentary rock are from other rocks, all of different ages. And the radioactive dating will only provide the age of the particles not the age of the sedimentary rock.
c. If a geologist finds a fossil in a layer of sedimentary rock that lies in between two igneous intrusions the geologist will determine the age of the fossil by using the law of super position or by determining the amount of a radioactive element in the rock and from there comparing the amount with the amount of the stable element into which the radioactive element decays.