Measuring/Understanding Time

Principle of Uniformitarianism:

                     The principle that the geological forces of the past differ neither in kind nor in energy from those now in operation. By its emphasis on the cumulative effect of slow actions over protracted periods of time, uniformitarianism implied a vast extension of geologic time.

Actualism:

                    The same forces presently in evidence acting over time with energies and frequencies similar to those now observable are the sufficient causes of all geologic records; related to episodicity; uniformitarianism with the caveat that rates are not necessarily constant

Catastrophism:

                  The doctrine that sudden violent, short-lived more or less worldwide events ouside our present experience or knowledge of nature have greatly modified the Earth's crust