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to, and usually known only to, specialists in that field. There is no formalized
biological time scale or chemical time scale, even though all processes de-
scribed in these two great disciplines have temporal components. All other
fields of study simply use the familiar intervals of time: seconds, minutes,
hours, days, and so on. Geologists, on the other hand, talk about periods and
epochs, eras and zones, stages and series—the vast subdivisions of what is
known as the geological time scale. Time is clearly indispensable to and in-
tertwined with the study of geology. Perhaps this is why geologists seem a bit
obsessed by time and its measurement and have been so since the birth of
their science.
Efforts to address the "time problem" in geology were historically
spurred by two quite different motives. The first began as essentially a reli-
gious pursuit but later became the most pressing scientific, question of the
late nineteenth century. Learned men (mainly theologians) were curious
about the age of the earth and how that age was related to the myriad myths
of the creation. The second prod was far more prosaic. Early geologists found
that they could more easily find economically valuable minerals and fuels if
they could understand the structure of the earth's surface. Very quickly, they
realized they needed some way to date rocks.
There has certainly been no lack of effort to answer these questions.
Finding the age of the earth was a quest long entrusted to theologians, who
searched not in the crustal record of the earth itself but among the sacred
writings of human prophets. Their answers varied between a few thousand
years and infinity. The Hindu tradition weighed in at slightly less than 2 bil-
lion years, whereas some Hebrew and Christian calculations yielded values
of less than 10,000 years. But as technology advanced, and the thirst not
only for religious understanding but also for metals and fossil fuels increased,
measurement grew more scientific.
With the onset of the Industrial Revolution, knowing the
age
of rocks
became a necessary prerequisite to finding industrial minerals, such as coal,
iron, and the other materials that fueled and sustaining the great Western in-
dustrialization of the eighteenth and nineteenth centuries. It was in the
mining regions where engineers, who needed a better system for organizing
