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A "quadrangle" is a topographic map produced by the United States Geological Survey (USGS) covering the United States. The maps are usually named after local physiographic features. The shorthand "quad" is also used, especially with the name of the map; for example, "the Ranger Creek, Texas quad". A quadrangle is defined by north and south ...
Author: Pease, M.H., Jr., and Monroe, W.H. Image title: Geologic map of the San Juan quadrangle, Puerto Rico; Short title: USGS Miscellaneous Investigations Series ...
Geologic time is the timescale used to calculate dates in the planet's geologic history from its origin (currently estimated to have been some 4,600 million years ago) to the present day. Radiometric dating measures the steady decay of radioactive elements in an object to determine its age. It is used to calculate dates for the older part of ...
Today's U.S. Topo quadrangle (1:24,000) maps are mass-produced, using automated and semiautomated processes, with cartographic content supplied from the National GIS Database. [33] In the two years from June 2009 to May 2011, the USGS produced nearly 40,000 maps, more than 80 maps per work day. [33]
The geologic time scale is a way of representing deep time based on events that have occurred throughout Earth's history, a time span of about 4.54 ± 0.05 Ga (4.54 billion years). [3] It chronologically organises strata, and subsequently time, by observing fundamental changes in stratigraphy that correspond to major geological or ...
Shaded relief map of the United States, showing 10 geological provinces. The richly textured landscape of the United States is a product of the dueling forces of plate tectonics, weathering and erosion. Over the 4.5 billion-year history of the Earth, tectonic upheavals and colliding plates have raised great mountain ranges while the forces of ...
Geologic time shown in a diagram called a geological clock, showing the relative lengths of the eons of Earth's history and noting major events. The geological history of the Earth follows the major geological events in Earth's past based on the geological time scale, a system of chronological measurement based on the study of the planet's rock ...
1911 – Arthur Holmes uses radioactivity to date rocks, the oldest being 1.6 billion years old; 1912 – Alfred Wegener proposes that all the continents once formed a single landmass called Pangaea that broke apart via continental drift; 1912 – George Barrow maps zones of metamorphism (the Barrovian sequence) in southern Scotland