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20 Cards in this Set

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isotopes
atoms of the same elements that have the same number of protons in their nuclei but a different number of neutrons, iotopes of the same element have different masses
geologic time scale
the division ofgeologic time into intervals in chronological ordr, based largelt on fossil evidence and on evidence of significant geologic events
halflife
the time required for one-half of an unstable atoms in a radiocative sample to decay to a different isotope
Paleozoic Era
the time period represents about 85% of Earth's geologic history
unconformity
a gap in rock record caused by the burial of an erosional surface by younger rocks or sediments
index fossils
fossils that are useful in correlating and dating rocks because of its wide geographic distribution and small vertical distribution
orginal horizontality
a principle that states that sedimentary rocks are originally formed in horizontal layers
mesozoic era
the time period represents abour 3.5% of Earth's geologic history
outgassing
the release of gasses from the interior of Earth due to internal heat and chemical reaction
bedrock
the solid, unweathered portion of the lithosphere
radiocactive decaay
the breakdown or the nuclei of unstable atomes into more stable atoms of the samer or other elements
Precambrian
the time period represents the first 85% of Earth's history
principle of superposition
the principle that states that in layered rocks the youngest layer is on top and the age of the other layers increases with depth
variations
natural changes within species
correlation
the matching or rock units or events in seperate rock formations
volcanic ash
small pieces of volcanic rock dispersed into the air during a volcanic eruption
cenozoic era
This era represents the most recent 3% of Earth's geologic history
absolute age
the actual age of a rock or event
geologic history
determined from fossil evidence, the age of the rocks, and the erosional record in the rocks
free oxygen
oygen not combined with other elements