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unit 4 vocab

TermDefinition
absolute age The age of a rock given as the number of years since the rock formed.
half-life The length of time required for half of the radioactive atoms in a sample to decay
radioactive decay A spontaneous process in which unstable nuclei lose energy by emitting radiation
carbon dating The determination of the age or date of organic matter from the relative proportions of the carbon isotopes carbon-12 and carbon-14 that it contains
relative dating Method of determining the age of a fossil by comparing its placement with that of fossils in other layers of rock
law of superposition The geologic principle that states that in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it.
law of horizontality In a sequence of sedimentary rocks, layers of rock were originally formed lying horizontally
law of uniformitarianism The idea that the same processes seen occurring now also occurred in the past
law of cross-cutting relationships Principle that a fault or intrusion is younger than any other body of rock it cuts through
law of inclusions If one rock body contains fragments of another rock body it must be younger than the fragments of rock it contains.
intrusion An igneous rock layer formed when magma hardens beneath Earth's surface.
extrusion An igneous rock layer formed when lava flows onto Earth's surface and hardens.
fault A crack in the earth's crust resulting from the displacement of one side with respect to the other
fossil A trace of an ancient organism that has been preserved in rock.
index fossil A fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found
meteorite A meteoroid that passes through the atmosphere and hits Earth's surface.
Created by: user-1996564
 

 



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