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PCS Earth Science

Chapter 21 - Fossils and the Rock Record

TermDefinition
altered hard parts fossils whose organic material has been removed and whose hard parts have been changed by recrystalization or mineral replacement
cast fossil formed when an earlier fossil of a plant or animal leaves a cavity that becomes filled with minerals or sediment
correlation matching of rock outcrops of one geographic region to another
cross-cutting relationships principle stating that a fault or intrusion is younger than the rock it cuts across
dendrochronology the process of counting tree rings to determine the age of a tree
eon longest time unit in the geological time sale, measured in billions of years
epoch time unit in the geologic time scale, smaller than a period, measured in millions of years to tens of millions of years
era second-longest unit of time in the geological time scale, measured in hundreds of millions of years, and defined by differences in life forms that are preserved in rocks
evolution adaptation of life-forms to changing environmental conditions
fossil remains or evidence of a once-living plant or animal
geologic time scale record of Earth's history from its origin to the present used to correlate geologic events, environmental changes, and development of life forms that are preserved in rocks
half-life period of time it takes for a radioactive isotope, such as carbon-14, to decay to one-half of its original amount
index fossil remains of plants or animals that were abundant, widely distributed, and existed briefly that can be used by geologists to correlate or date rock layers
key bed a single, widespread rock layer that is unique and easily recognizable; used to correlate rock layers
mold fossil that can form when a shelled organism decays in a sedimentary rock and is weathered away, leaving a hollowed out impression
original horizontality principle stating that sedimentary rocks are deposited in horizontal or nearly horizontal layers
original preservation describes a fossil with soft and hard parts that have not undergone any change since the organism's death
period third-longest time unit in the geological time scale, measure in tens of millions of years to hundreds of millions of years, and defined by life-forms that were abundant or became extinct
permineralization process in which pore spaces in a fossil are filled in with mineral substances
radioactive decay emission of atomic particles at a constant rate from a radioactive substance and its resulting change into other elements over time
radiometric dating process used to determine the absolute age of a rock or fossil by determining the ratio of parent nuclei to daughter nuclei within a given sample
superposition principle stating that in an undisturbed rock sequence, the oldest rock layers are at the bottom and each successive layer is younger than the layer beneath
uncomformity gap in the rock record caused by erosion or weathering
uniformitarianism states that processes such as mountain building, erosion, and sea-level changes that are occurring today have been occurring since Earth formed
varve a banded layer of sand and silt that is deposited annually in a lake, especially near ice sheets or glaciers, and that can be used to determine absolute age
Created by: Ms.Sala
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