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Lesson 7: Geologic Time
Terms in this set (28)
History of the earth based on the fossil record and divided into eras, periods, and epochs. Based on major changes in Earth's surface, climate, and types of organisms
consists of the Hadean, Archean, and Proterozoic Eons; before macroscopic life; accounts for 84% of geologic time
included 5 mass extinctions: Cretaceous/Tertiary (KT)*
how old is earth?
Geologic Time Scale (GTS)
the categories of time into which Earth's history is usually divided by geologists and paleontologists: eons, eras, periods, epochs; first was developed using relative dating techniques then added numeral ages with absolute dating techniques in the 1950s
age of units relative to one another found by observed contact relationships between rock units.
compare fossils in the unit in question to fossils/fossil assemblages in the evolutionary sequence of fossil forms
specific age of a unit in years found through radioactive decay of isotopes in minerals
Principle of Superposition
the principle that in a series of stratified sedimentary rocks the lowest stratum is the oldest
Principle of Original Horizontality
The principle that states that layers of sediment are generally deposited in a horizontal or nearly horizontal position.
principle of cross-cutting relationships
Igneous intrusions and faults are younger than the rocks they intrude or break.
fractures along which there has been movement of one side relative to the other due to brittle failure; result from compressional, tensional, and shear stress; includes dikes, sills and batholiths,
principle of baked contacts
Igneous rocks will bake or metamorphose adjacent rocks, indicating that the igneous rocks intruded after the deposition of the other rocks.
principle of fossil succession
Specific fossil assemblages succeed one another in the rock record in a definite order (evolution); relies on the idea that species have changed through time and once a fossil species disappears, it will not appear higher in the strata.
the interface between two rock units of different ages that represents missing time due to erosion.
tilted rocks are overlain by flat-lying rocks
A type of unconformity in which layered sedimentary rocks lie on an erosion surface cut into igneous or metamorphic rocks
a type of unconformity in which the sedimentary layers above and below the unconformity are parallel
a unique layer present over a broad area that aids correlation.
an arrangement of rock layers in which the oldest rocks are at the bottom: represents almost all of Earth history
Extinction Recovery Stages
1. Survival: adaptation and reproduction
2. Diversification: ecological vacuum with open ecological niches = greater opportunity for expression of genetic variations = rapid radiation and an increase in diversity
3. Stabilization: increased competition reduces the rate of evolution and a new ecosystem is created
made of protons (+) and neutrons (0) in the nucleus and orbiting electrons (-).
number of protons
Number of protons and neutrons
atoms of a single element that have different number of neutrons but the same number of protons in their nuclei.
the change in which unstable parent
isotopes turn into stable daughter isotopes; spontaneous and irreversible ex: popping popcorn
the time it takes for half of the present parent material to decay to the daughter product at any given time.
the temperature below which isotopes are no longer free to move
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