Glossary of Chapter 6 Earth's History

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What is the process of matching rocks and geologic events in one location with rocks and geologic events in other locatins?
What is the release of gasses from the interior of Earth due to internal heat and chemical reaction?
What is free oxygen?
Free oxygen is oxygen not combined with other elements
At the end of one half-life, ____ the atoms of a radioactive sample remain, and at the end of two half lifes, _____ will remain.
one half, one fourth
What is the half-life of a substance?
It is the time it takes one-half of the atoms of that substance to decay to another element.
What is Uranium 238 useful for?
It is useful in determining radioactive dating.
What is radioactive decay?
Radioactive decay occurs when the nucli of unstable atoms break down or decy giving off particles and energy.
What is the Geologic Time Scale, and what are its parts?
The Geologic Time Scale is a division of geologic time into units based on fossil evidance. Its parts are Precambrian, Palezoic Era, Mesozoic Era, and Cenozoic Era
What are the four steps that combine in sequence to form an unconformity?
uplifting, erosion, subsidance (submerging), and deposition.
What is outcrop?
Bedrock exposed at Earth's surface
The presence of faults, joints, and folds indicates that some force was exerted on the rocks ________.
In the past.
If contact metamorphism has altered the rocks above and below the igneous rocks, the mass must be an _________.
Intrusion, the magma forced its way between the two layers of rocks.
What are unconformities?
Buried erosional surfaces, which indicate gaps or breaks in the geologic time record.
What is a joint?
A joint is a crack in a rock formation. In a joint, there is no displacement.
What are angular unconformities?
They consist of tilted, forlded, or faulted rocks which have been eroded and then covered agian.
What is a species?
A group of organisms that can mate and produce fertile offspring
The older a rock is, the harder it is to determine it's __________, the ________________ of a rock is easier to determine.
Absolute age, Relitive age
What is the geologic history of an area primarily determined by?
fossil evidance, the ages of the rocks and the erosional record in the rocks.
What does radioactive decay change the origional atoms to?
atoms of another element
What are Nonconformities?
They are formed when sedimentary rocks are deposited on top of an eroded surface of igneous rocks.
What are parallel unconformities, or disconformities?
The occur when parellel rock layers of different ages are separated by an erosional surface.
Cracks, veins, and mineral cement are _____ then the rocks in which they appear.
What is a vein?
A vein is a mineral deposit that has filled a crack or permeable zone in existing rock.
Rock fragments found in larger rock masses are ______ then the rock in which they appear.
What is a break or gap in the rock record?
A hiatus
What are anomalies?
Anomalies are deviations from what is expected.
The rock layer beneath the igneous mass shows evidance of contact metamorphism, it indicates that the igneous mass is most likely an _____.
What is the solid, unbroken rock of the crust?
What are isotopes?
Atoms of the same element that have the same number of protons and different numbers of neutrons in their nucli
What are fossils or organisms that lived over an extensive area-preferably over the entire Earth-for relatively short periods of time
Index fossils
What is extrusion?
When lava solidifies at Earth's Surface, it form a mas of ignous rock.
What is the principle of original horizontality?
This states that sediments are deposited in horizontal layers that are parellel to the surface on which they were deposited, therefore, tilted or folded layers indicate that the crust has been deformed.
What is geologic history?
Geologic history is the study and interpretation of Earth's past.
What is the principle of uniformitarianism?
A principle stating that the geological process in action today are the same as those that acted in the past, thus allowing us to interpret the events of the pst by studying events currently taking place.
Below an extrusion, the rocks are ________ then the extrusion.
Since the rocks through which the magma moved existed prior to the instrusion, they must be ______ then the intrusion.
What is when the age of a rock or event is compared to the ages of other rocks or events in a geologic sequence?
Relative age
What is the actual age of a rock or event?
Absolute age
What is intrusion?
When molen magma forces its way into cracks or crevices in crustal rock solidifies.
When does the principle of superposition not apply?
when layers have been overturned or where older rocks have been forced over younger layers along a fault.
What is the principle of superposition?
It states that in a series of undisturbed layers, the oldest layer is on the bottom and each successive overlying layer is progressively younger

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