1978, George Vincent Cohee, Martin Fritz Glaessner, Hollis Dow Hedberg, editors, Contributions to the Geologic Time Scale[…], American Association of Petroleum Geologists, →ISBN, page 34:
Geologic time is simply time used in the context of earth history, determined by geologic methods. Our only record of the passage of geologic time lies in the Earth's rock strata. This record is imperfect, but it is our only one.
