In the Geologic Time Scale, time is generally divided on the basis of the earth's biotic composition, with the Phanerozoic Eon (i.e.the Paleozoic, Mesozoic and Cenozoic Eras) representing the period of Earth's history with advanced life forms, and the Pre Cambrian (or Proterozoic and Hadean Eras) representing the period before advanced life.To help students understand the development of the geologic time scale.Also, to introduce students to the major time periods in earth's history, as well as to the role fossils play in helping us understand this history.The last glacial period ends with the cold Younger Dryas substage.It has been identified with the current warm period, known as MIS 1, and is considered by some to be an interglacial period.
The 'Anthropocene' is not a formally defined geological unit.Older periods which predate the reliable fossil record are defined by absolute age.Each era on the scale is separated by a major and/or changing event.**If the images and/or text on any of the web pages do not appear evenly spaced and centered on your screen, which commonly occurs with AOL pages, maximize the individual page's window. This lesson is based on an online booklet that provides an introduction to the study of earth's history, published by the USGS.Using careful analogies and written historical records, the authors help students understand the development of the geologic time scale, including how this depended on gathering evidence and making comparisons.Since publication of a chart showing divisions of geologic time in the seventh edition of the USGS guide Suggestions to Authors (Hansen, 1991), no other time scale has been officially endorsed by the USGS. M., 2008, The concise geologic time scale: Cambridge, U.