Ch.9 definitions-science
This is a set of ch.9 definitions from the 7th grade glencoe science book.
Terms
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- unconformity
- gap in the rock layer due to erosion or periods without any disposition
- fossil
- remains, traces, or imprints of a plant or animal preserved in Earth's crust since some past geologic or prehistoric time
- index fossil
- remains of species that existed on earth for a relatively short period of time, were abundant and wide spread geographically, and can be used by geologists to assign the ages of rock layers
- cast
- a type of body fossil that forms when crystals fill a mold or sediments wash into a mold and harden into rock
- principle of superposition
- states that in undisturbed rock layers, the oldest rocks are on the bottom and the rocks become progressively younger toward the top
- radioactive decay
- release of nuclear particles and energy from unstable atomic nuclei
- half-life
- time needed for one-half the mass of a sample of a radioactive isotope to decay
- permineralized remains
- fossils in which the spaces inside are filled with minerals from groundwater
- radiometric dating
- process used to calculate the absolute age of rock by measuring the ratio of parent isotope to daughter product in a mineral and knowing the half-life of the parent
- uniformitarianism
- principle stating that Earth processes occuring today are similar to those that occured in the past