Topic 13 Interpreting Geologic History Vocabulary

inclusion
Body of older rock within igneous rock
extrusion
Lava flows on the Earth’s surface and solidifies
volcanic ash
Consisting of sand sized and clay sized particles of extrusive igneous rocks shot into the air
intrusion
Magma squeezes into preexisting rocks and crystallizes
absolute age
Actual age of the rock or an event in years
evolution
States that life forms change through time
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bedrock
An area’s local rock covered by soil and other loose materials
radioactive decay
Emission of particles and electromagnetic energy
index fossils
Fossils used in correlation that have lived over a wide geographic area and are short lived
principle of superposition
Rocks are deposited in layers with youngest on top, oldest on the bottom
relative dating
Determination of the age of a rock in relation to other rocks or events
unconformities
Evidence of buried eroded surfaces
carbon-14
Useful isotope with a half life of 5700 years that is used to date fossils or organic remains
fossils
Remains or evidence of former living things (bones, shells, footprints…)
outgassing
Gases from the Earth’s interior seeped out of the crust through cracks in the crust and volcanoes
half-life
Time required for half of the atoms in a given mass of an isotope to decay
isotopes
Elements exist in several different varieties
radioactive dating
Method used to estimate the absolute age of a rock
geologic time scale
Divisions of geologic time (Eons, Eras, Periods, Epochs) make up this chart
uranium-238
Important radioactive isotope used in dating very old rocks