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Geologic Time Unit

unit 3 vocabulary

TermDefinition
fossil the preserved remains or traces of living things
sedimentary rock the type of rock made from hardened sediments, where fossils are most commonly found
mold a hollow area in sediment in the shape of all or part of an organism
cast a solid copy in the shape of an organism, forms when minerals are deposited in a mold
petrified fossil fossils in which minerals replace all or part of an organism
carbon film an extremely thin coating of carbon on rock
trace fossil provides evidence of the activities of ancient organisms (footprints, trails, burrows)
paleontologist scientist who studies fossils
scientific theory a well tested concept that explains a wide range of observations
evolution the gradual change in living things over long periods of time
extinct something that no longer exists and never will live on Earth again.
relative age the age of a rock compared to the ages of other rocks (tells older or younger)
absolute age the number of years since the rock formed
law of superposition used to determine the relative ages of sedimentary rocks; in horizontal rock layers, the oldest layer is at the bottom and each layer higher is younger than the one below it
extrusion lava that hardens to form rock on the surface of the earth (are younger than the rock layers beneath it)
intrusion magma that hardens to form rock beneath Earth's surface (are younger than the rocks around it)
fault a break in earth's crust (younger than the rock it cuts through)
unconformity a gap in the geologic record made by a younger layer of rock meeting a much older layer beneath it
index fossil certain fossils that are widely distributed and represent a type of organism that lived only briefly which helps geologists match and date rock layers.
atom tiny particles of matter
element matter in which all the atoms are the same
radioactive decay certain atoms break down to form atoms of another element releasing particles and energy
half-life the amount of time it takes half of and element's radioactive atoms to decay
geologic time scale the record of life forms and geologic events in Earth's history
era larger divisions of geologic time
period subdivisions of eras
Cenozoic Era The era we presently live in - referred to as the "age of mammals"
Mesozoic Era the "age of reptiles" - dinosaurs were a major life form during this era
Paleozoic Era The earliest era of geologic time
Created by: sdix
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