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22 Cards in this Set
- Front
- Back
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Lateral continuity
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sedimentary layers generally accumulate in sheets that cover broad areas.
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What is the difference between relative and absolute ages?
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Relative - establish the order in which events occurred, but do not give numerical dates.
Absolute - fix numerical dates on events. Relative ages are fast, easy, cheap, and abundant. |
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7 Principles for relative ages...
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Principle of Superposition
Original Horizontality Lateral continuity Cross-cutting relations Principle of Inclusion Principle of Baked Contacts Principle of Faunal Succession |
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Principle of Superposition
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sedimentary rock layers, the layers at the bottom are older than those at the top
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Original Horizontality
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Gravity causes sediments to accumulate in generally horizontal layers
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Cross-Cutting Relations
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If one geologic feature cuts across another, the cut feature is older.
Sedimentary beds were (1) originally horizontal and (2) originally laterally continuous. (3) Oldest beds are on bottom. (4) Faults younger than beds. |
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The Principle of Inclusion
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If a body of rock contains fragments of another rock, the included rock fragments must be older than the enclosing rock body. (The fragments had to exist first in order to get incorporated.)
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Principle of Baked Contacts
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A rock that has been baked (contact metamorphosed) is older than the intrusion that did the cooking.
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Principle of Faunal Succession
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If you collect fossils in a sequence of sedimentary layers, their relative ages are defined by the principle of superposition.
Each fossil species occupies a unique interval of geologic time. |
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Who was Nicholas Steno?
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17th century, first to realize that the Earth has a history recorded in its rocks.
Articulated the principles of original horizontality, lateral continuity, and superposition. Fossils proved past life. |
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Who was Hutton?
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Principle of Uniformitarianism - physical processes that we observe today are the same ones that acted in the past to produce the geologic record we observe.
The present is the key to the past. Also the first to realize the Earth has a LONG history. |
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What is an unconformity?
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the surface representing the missing time in a sedimentary record.
Sedimentation is rarely continuous for long. |
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The Angular Unconformity
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when layers below the unconformity are tilted or folded relative to the layers above the unconformity.
Folding or faulting and uplift assoc. mountain building. Erosion and subsidence back down to sea level. More sediment accumulation once surface is below sea level. |
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Hard rock unconformity
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where sedimentary layers overlie intrusive rocks or metamorphic rocks.
Reflects intrusion + much erosion + sedimentation. |
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Soft rock unconformity
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forms where a drop in sea level or a change in local currents or sedimentation conditions results in erosion or non-deposition.
Reflects sea level changes. |
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Why does changing the number of protons affect the chemistry of atoms and thus define what element it is? Why does adding neutrons to the nucleus have no effect on the chemistry of an element? Diff. between isotope & an element?
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Number of protons determines number of electrons. Electrons determine chemistry of atoms.
Isotopes have same # of protons, diff neutrons. |
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Depleted uranium and enriched uranium...
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U enriched in 235U
U depleted in 235U |
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Is the rate @ which radioactive elements decay constant, or change over time?
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constant, decay constants
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What is a half-life?
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how long it takes one-half of the starting amount of a given parent to decay to its daughter.
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What was the first step in constructing the geologic time scale.
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principle of superposition
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What is the commonly cited age of the Earth? What event does it actually represent?
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4.57 Byr old.
Age of the formation of the first solids in the Solar System. |
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How does the slope of an isochron relate to age?
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The older the rock, the steeper the slope. Slope of the line gives the age of sample.
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