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ch 15 science vocab
Question | Answer |
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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. |