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. For consistent usage of time terms, the USGS Geologic Names Committee (GNC; see box for members) and the Association of American State Geologists (AASG) developed Divisions of Geologic Time (fig. (Also available at Ogg, Gabi, comp., 2009, Global boundary stratotype sections and points (GSSP): International Commission on Stratigraphy, accessed May 10, 2010, at By modern scientific calculations, the earth is many millions of years old.The Absolute Geologic Time Scale has been developed by using a process called “Isotopic Dating”, in which the decay rates of certain radioactive materials are established and measured, then used as “clocks” to calculate the ages of various rocks.Principles of Stratigraphy Stratigraphy is the study of strata (sedimentary layers) in the Earth's crust.
The chart shows major chronostratigraphic and geochronologic units. O., and others, 2009, Formal definition and dating of the GSSP (global stratotype section and point) for the base of the Holocene using the Greenland NGRIP ice core, and selected auxiliary records: Journal of Quaternary Science, v.
By carefully digging, we have found that each trash pit shows a sequence of layers.
Although the types of trash in each pit is quite variable, each layer has a distinctive kind of trash that distinguishes it from other layers in the pits.
to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth.
The table of geologic time spans presented here agrees with the dates and nomenclature proposed by the International Commission on Evidence from radiometric dating indicates that the Earth is about 4.570 billion years old.