What is the main criterion that scientists use to decide where to place the boundaries between the major divisions of the geologic time scale?

The main criterion that scientists use to decide where to place the boundaries between the major divisions of the geologic time scale is C. major changes that are recorded in the fossil record.

These are the options for the question below.

A. major changes in the structure of Earth's layers

B. major changes that occur in the solar system

C. major changes that are recorded in the fossil record

D. major changes in the  arrangement of the continents.

The geologic time scale  can be regarded as the calendar” for events in Earth history and this is been sectioned named units of abstract time

It should be noted that scientists use to decide where to place the boundaries between the major divisions by major changes that are recorded in the fossil record.

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Out of the following given choices;

A. major changes in the structure of Earth's layers

B. major changes that occur in the solar system

C. major changes that are recorded in the fossil record

D. major changes in the  arrangement of the continents

The answer is C. Changes in the environment in prehistoric times can be best exhibited by the evolutionary changes of living organisms. This is best shown by fossil records. Changes in geological times are characterized by a high rate of varying individuals of a species and with high extinction rates.