What is geologic time ? a)the period before humans appeared on earth b)a unit of time used to measure rock formation c)a period of time during which only rocks existed d)the time that has passed since earth formed

the correct answer is:

a population changes in response to a change in the environment.

the rocks are classified by the geological process they are formed by. the three main groups of rocks are igneous, metamorphic, and sedimentary. minerals are not they are classified under the chemical classes they are in. these groups include silicates, sulfates and carbonates.