ANSWER
(B) Scientists developed the geologic time scale by studying rock layers and index fossils worldwide.
EXPLANANTION:
The sedimentary rocks found in these rock layers are known as strata. These rocks are formed by the three major processes; accumulation, compaction and cementation of sediments. Analysis of these rocks can give the geologists a clear idea about the timescale. Studying its composition, dating, appearance and etc the geologists can easily develop a time scale.