Scientists used major changes in life forms in the fossil record to form the geologic time scale.

That statement is True

major changes in life forms in the fossil indicates that the organisms were most likely made an physiological adaptation to survive in a completely new environment. This indicates the geologic change which can be used as a time frame to distinguish one period with another.

There is no direct questions available in the statement but I am assuming that you are asking whether the statement is correct or incorrect. Scientists did not perform any changes in fossil record to form the geologic time scale. Whatever they have dug up, is enough evidence to piece together incomplete information from the past that can be of used at present and in the near future.