How do scientists define the segments of the geologic time scale?
a. the scientists study fossils in rock layers to find major changes
b. the scientists use fixed amounts of time for each segment
c. they do both of these
d. they do neither of these

The answer of the given question above would be option C. The scientists define the segments of the geologic time scale by studying fossils in rock layers to find major changes and using  fixed amounts of time for each segment. The answer would be both options A and B. Hope this answer helps.

Ten percent of energy is transferred from sun to the level indicated.