Unit 2 Ch 8 Vocab Flashcards
(26 cards)
relative time
the sequence in which events took place; not measured in time units
principle of superposition
a principle stating that within a sequin of undisturbed sedimentary rocks, the oldest layers are on the bottom, the youngest on the top
uniformitarian model
it must take a very long time for weathering/erosion to produce any significant change in the shape of Earth’s surface
unconformities
a surface that represents a break in the geologic record, with the rock unit immediately above it being considerably younger than the rock beneath
principle of cross-cutting relationships
a principle or law stating that a disrupted pattern is older than the cause of the disruption
principle of inclusions
fragments included in a host rock are older than the host rock
fossils
the preserved trace, imprint, or remains of a plant or animal
trace fossils
trail, track, or burrow resulting from animal movement preserved in sedimentary rock
eon
the largest unit of geological time
Phanerozoic eon
the part of geologic time represented by rocks containing abundant fossil evidence. The eon extending from the end of the Proterozoic eon to the present
Proterozoic eon
the eon following the Archean and preceding the Phanerozoic
Archean
a term, meaning ancient, which has been applied to the oldest rocks of the Precambrian
cenozoic era
the most recent of the eras; also known as the Age of Mammals
mesozoic era
the era that followed the Paleozoic era and preceded the Cenozoic era
paleozoic era
the era that followed the Precambrian and began with the appearance of complex life, as indicated by abundant fossils
precambrian
the vast amount of time that preceded the Paleozoic era
Cretaceous-Tertiary extinction
K-T event; time about 65 million years ago when 70% of species became extinct, including dinosaurs
Permian-Triassic extinction
P-T event; time about 251 million years ago that marked the largest mass extinction event known on Earth
radioactive decay
the process by which unstable (radioactive) isotopes transform to new elements by a change in the number of protons (and neutrons) in the nucleus
parent isotope
radioactive isotope that decays through time to a daughter isotope
half-life
the time required for one-half of the atoms of a radioactive substance to decay
numerical time
amount of time elapsed as determined by analyses of the decay of naturally occurring radioactive elements
catastrophism
the concept that some Earth features are shaped by catastrophic events of a short-term nature
uniformitarianism
principle that geologic processes operating at present are the same processes that operated in the past. the principle is stated more succinctly as “the present is the key to the past”
