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ch 15 science vocab

uniformitarianism the principle that states that the same geologic processes shaping the earth today have been at work throughout earths history.
catastrophism the idea tht all geologic change happens suddenly.
relative dating the process of determining the order in which events happened; also used to compare ages of objects, such as rocks or fossils.
superposition the principle that younger rocks lie above older rock unlessthe layers have been disturbed.
geologic column an ideal sequence of rock layer that contains all known rock formations and fossils on earth arranged from oldest to youngest.
uncomformity a surface that represents a missing part of the geologic column.
absolute dating the process of dating by determining the number of years that the object has existed.
isotope an atom that has the same number of protons as other atoms of the same element but different numbers of nuetrons.
radioactive dating the process of analyzing the ratio of parent and daughter material in a sample to determine the samples absolute age.
half-life the amount of time one-half of a radioactive sample takes to decay.
fossil the remains or physical evidence of an organism preserved by geologic processes commonly preserved in sedimentary rock.
paleontologist a scientist who studies fossils.
trace fossil any naturally preserved evidence of animal activity.
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 used to establish the age of a rock layer because the fossil is distinct, abundant, and widespread and the species that formed that fossil existed for only a short span of geologic time.
geologic time scale the standard method used to divide the earths long natural history into manageable parts.
Created by: MadelynI