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Ch6 Mr.Lucy
Question | Answer |
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uniformitarianism | a principle that geologic processes that occurred in the past can be explained by current geologic processess |
catastrophism | a principle that states that geologic change occurs sudemly |
palentology | the scientific study of fossils |
relative dating | any method of determining whether an event or object is older or younger than other evnts or objects |
super position | a principle that states that younger rocks lie above older rocks if the layers have not been disturbed |
geologic column | an orderd arrangement of rock layer that is based in the relative ages of the rocks and in which the oldest rocks are at the bottom |
uncomformity | a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time |
absolute dating | any method of measuring the age of an event or object in years |
isotapes | an atom that has the same number of protons (or the same atomic number) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mass) |
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 | a method of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope |
half life | the time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope |
fossil | the trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock |
trace fossils | a fossilized structure, such as a footprint or a coprolite, that formed in sedimentary rock by animal activity on or within soft sediment |
mold | in biology, a fungus that looks like wool or cotton |
cast | a type of fossil that forms when sediments fill in the cavity left by a decomposed organism |
index fossils | 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 Earth's long natural history into manageable parts |
eons | the largest division of geologic time |
eras | a unit of geologic time that includes two or more periods |
periods | in geology, a unit of geologic time that is longer than an epoch but shorter than an era |
epochs | a subdivision of geologic time that is longer than an age but shorter than a period |
extinction | the death of every member of a species |