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8th grade Ch 6

Geologic Time

QuestionAnswer
Trace fossil evidence of the activities of an ancient organism
absolute age the number of years that have passed since the rock formed
relative age the age of a rock compared to the ages of other rocks
extrusion Lava that hardens and forms igneous rock
intrusion magma that cools and hardens before it reaches the surface
index fossil fossils that are wide spread, from an organism that lived only a short geologic period of time, useful to determine relative age
radioactive dating method used by scientist comparing the radioactive decay of an element to that of a stable element to determine the absolute age of the rock
unconformity a gap in the geologic record
half-life the time it takes for half of the radioactive atoms to decay in a radioactive element
cross-cutting the principle that states that if a fault or intrusion cuts across another layer, then it must be younger than those layers
Law of Superposition if undisturbed, sedimentary rocks will be in horizontal layers with the oldest rock at the bottom and the youngest on the top
Created by: KimRoush
 

 



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