If you are examining rock layers that are suspected to be about 20 million years old, which radioactive isotope would you use? Explain your answer

Unlike venus and mars, earth's atmosphere is primarily composed of oxygen and nitrogen. why is the composition of earth's atmosphere different from the composition of the atmospheres of venus and mars? a. earth has life, while venus and mars do not. b. venus and mars are slightly smaller than earth. c. venus, mars, and earth all have similar chemical compositions. d. venus and mars have different chemical compositions from earth.