Coral and absolute dating
This is where radioactive methods frequently supply information that may serve to calibrate nonradioactive processes so that they become useful chronometers.
Nonradioactive absolute chronometers may conveniently be classified in terms of the broad areas in which changes occur—namely, geologic and biological processes, which will be treated here.
And, if glacial time and nonglacial time are assumed approximately equal, the Pleistocene Epoch lasted about 1,000,000 years.
Only one weathering is the time since the surface examined was freshly exposed.
This relationship is confirmed both by laboratory experiments at 100° C (212° F) and by rim measurements on obsidian artifacts found in carbon-14 dated sequences.
Practical experience indicates that the constant is almost totally dependent on temperature and that humidity is apparently of no significance.
In the American Midwest, thicknesses of gumbotil and carbonate-leached zones were measured in the glacial deposits () laid down during each of the four glacial stages.
Based on a direct proportion between thickness and time, the three interglacial intervals were determined to be longer than postglacial time by factors of 3, 6, and 8.