1. The Eras of Geologic Time
... based upon relative age relationships (most commonly, vertical/stratigraphic position). These subdivisions are given names, most of which can be recognized globally, usually on the basis of fossils. • Absolute time ("chronometric") -- numerical ages in "millions of years" or some other measurement. These are most commonly obtained by using radiometric dating methods performed on appropriate rock types. Some of the ... the temporal reference. Prior to about 1965 the spelling pre-Cambrian prevailed, and this form still is preferred by some, notably those who favor the establishment of a...
- Word Count: 1841
- Approx Pages: 7
- Grade Level: Undergraduate