What is paleontology?
Paleontology is the study of fossils. A fossil is defined as any preserved remains or traces of a past life form. Paleontologists study fossils to reconstruct the history of the Earth and the life on it.
What does the Exploring Time and Space map portray?
The map used here was created by the US Geological Survey in Menlo Park.
Through computer processing and enhancement, they wove together the
Why do some of these maps look different than other geologic maps of the same area and time period?
For purposes of the web, the USGS map has been simplified from a more detailed geologic map. It was meant to indicate the major exposures of rocks of a particular time interval.
What does the colored column portray?
The colored column represents intervals of geologic time. The colors correspond to those used in the map and are more or less consistent with those used as the Sedimentary Age Colors of the U.S. Geological Survey: http://geopubs.wr.usgs.gov/open-file/of99-430/of99-430_sec33.pdf
What is the geologic time scale?
The geologic time scale is a sequential arrangement of time units defined by geologists. It was based originally on two fairly simple observations. The first was that, given a stack of sedimentary rock layers, each layer of rock must be younger than those below it and older than those above it. The second observation was that the presence or absence of various life forms also occurred in a predictable order. Taken together, these observations enabled scientists anywhere in the world to tell the relative age of rocks containing fossils.
Geologists subdivide time hierarchically into eras (e.g. Paleozoic, Mesozoic, and Cenozoic), which are further divided into periods (e.g. Cambrian, Permian, Cretaceous), which are further divided into epochs (e.g. Miocene, Pleistocene). Scientists also have a method for determining the actual number of years ago that various rocks formed. This method is called radiometric age dating, and it has allowed scientists to continue refining the accuracy of the geologic time scale.
What are undifferentiated rocks?
These are rocks for which finer age divisions are not specified on the map. In some cases this is because small areas of rocks of different ages are too close together to be shown at the scale of the map. In other cases, the exact age relationships of the rocks in a given area may not yet have been determined.
What are fossil assemblages?
This term can have several meanings, depending on how it is being used. The simplest meaning is "a collection of fossils that occur together in the same layer or layers of rock."
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Using radiometric dating: http://pubs.usgs.gov/gip/geotime/radiometric.html