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| In undisturbed sedimentary strata, the oldest layers will always be on the bottom. |
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| Sedimentary strata tend to be deposited in flat layers |
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| Original Lateral Continuity |
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| Sedimentary strata extend in all directions until encountering a barrier, or change in grade. |
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| The study of layered rocks |
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| The principle that the processes acting on the earth today are the same ones that acted on the earth in the past. |
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| separation of sedimentary strata from an igneous or metamorphic body |
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| Separation of sedimentary strata by an erosional surface |
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| Cross Cutting Relationships |
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Definition
| Features like dikes,sills,or faults that cut across pre-existing strata, and therefore must be younger than the layers they cut across. |
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| Fragments of rock enclosed in larger bodies of rock must be older than the rock in which they are enclosed |
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| Inclusion of a different rock type within another |
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| The alteration of rocks by contact with hot magma. The meta rocks were altered by the igneous intrusion, and therefore must be older |
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| Principle of Fossil Succession |
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Definition
| Strata at any given location contain fossils in a definite sequence, the same sequence can be found in other locations. Strata can be correlated by this principle. |
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| The temperature at which a mineral crystallizes, and thus the clock for radiometric dating starts |
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| The use of radiometric isotopes to determine an absolute age for rocks +/- .1% |
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| As U238 decays, it leaves trails of damage in layer lattice silicates. Counting the number of scars can give an age of +- 10% accuracy. |
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| Used for fossils less than 50,000in age |
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| Global Boundary Stratotype Point GBSP |
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| An internationally recognized geologic boundary |
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| Beds of sediment where where larger particles are on the bottom, indicates rapid settling in turbid conditions |
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| Formed by flows over a cohesive bed of mud |
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| Load Cast/Flame Structures |
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| Form as sediments are deposited rapidly and begin to settle out be density |
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| Preserved parts or impressions of and organism |
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| Evidence of prehistoric activity |
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| The filling of empty space in fossils with SiO2 |
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Definition
| The reorganiization of pre-existing minerals into more stable forms Destroys detail |
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| Molecule for molecule replacement usually by quartz or pyrite. Detail Preserved |
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| When a species becomes reproductivley isolated |
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| Remnants or bodyparts present in ancestral species |
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| The direction in which a compass neddle points |
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| The tilt of magnetic minerals relative to the horizontal (lattitude) |
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| When a river breaks its levee and leaves a deposit of sand |
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