27 terms

Science Chapter 6 Vocabulary

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uniformitarianism
a principle that states that geologic processes that occurred in the past can be explained by current geologic processes
catastrophism
a principle that states geologic change occurs suddenly
paleontology
the scientific study of fossils
relative dating
any method of determining whether an event or object is older or younger than other events or objects
superpostion
a principle that states that younger rocks lie above older rocks if the layers have not been disturbed
geologic column
an arrangement of rock layers in which the oldest rocks are at the bottom
unconformity
a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time
disconformity
an unconformity-found where part of a sequence of parallel rock layers are missing
absolute dating
any method of measuring the age of an event or object in years
isotope
an atom that has the same number of protons as other atoms of the same element do but has a different number of neutrons
radioactive decay
the process in which a radioactive isotope tends to break down into a stable isotope of the same element or another element
radiometric dating
method of determining the age of an object by estimating the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope
half life
time needed for half of a sample of a radioactive substance to undergo radioactive decay
fossil
the remains or physical evidence of an organism preserved by geological processes
trace fossil
a fossilized mark that is formed in soft sediment by the movement of an animal
mold
a mark or cavity made in a sedimentary surface by a shell or other body
cast
a type of fossil that forms when sediments fill in the cavity left by a decomposed organism
index fossil
a fossil that is found in the rock layers of only one geologic age and that is used to establish the age of the rock layers
geologic time scale
the standard method used to divide the Earth's long natural history into manageable parts
eon
the largest division of geologic time
era
a unit of geologic time that includes two or more periods
period
a unit of geologic time into which eras are divided
epoch
a subdivision of a geologic period
extinction
the death of every member of a species
Paleozoic Era
Ended with the largest mass extinction in Earth's history about 248 million years ago
Mesozoic Era
Age of Reptiles, began about 251 million years ago
Cenozoic Era
known as the Age of Mammals, began 65 million years ago.