The geologic time scale is a record of __________ and ___________.

Which of the following is the largest division of time on the geologic time scale? a. period, b. era, c. epoch, d. eon.

What information does the fossil record provide?

A rock from the moon contains 12.5% of the potassium-40 it began with. How old is the rock? (Hint: 12.5% = $\frac{1}{8}$)

A geologist finds an area of undisturbed sedimentary rock. The _____ layer is most likely the oldest.

A radioactive decay occurs when __________.