GEOlogic TIME GEO 2

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GEOlogic TIME GEO 2
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2010-06-21 02:48:17
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GEOlogic TIME GEO
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GEOlogic TIME GEO 2
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  1. Birth of Modern Geology
    • A. JAMES HUTTON
    • B. UNIFORMITARIANISM- the present is the key to the past
  2. Relative Dating (Placing events in order of occurence)-Key principles
    • A. LAW OF SUPERPOSITION
    • 1. In an undeformed sequence of sedimentary rocks, each bed older than the one above and younger than the one below it.
    • B.PRINCIPLE OF ORIGINAL HORIZONTALLY
    • 1. Layers of sediment are deposited in a horizontal position
    • 2. If rocks are folded or steeply dippin, they must have been moved to that position after deposition
    • C. PRINCIPLE OF CROSS-CUTTING RELATIONSHIPS
    • -fault or igneous intrusion cuts across rock layers is younger than the rocks it disrupts
    • D.INCLUSIONS
    • 1. Pieces one rock contained within another rock
    • 2.Inclusions are always older than the rock they are contained in
    • a. Xenoliths-inclusions in igneous rocks
    • b. Clasts-inclusion in sedimentary rocks
    • E. UNIFORMITIES
    • 1. Comfortable sequence-sequence of rocks have been deposited w/out interruption
    • 2. Unconformities
    • a. Buried surfaces of erosion or nondeposition
    • b.Time during which depostion stopped, erosion occured, then deposition resumed
    • 3. Types of unconformities
    • a. Angular unconformity- Erosional surface developed on titled or folded rocks overlain by younger, flat lying strata.
    • b. Disconformity- Strata on either side of the unconformity are essentially parallel
    • c. Nonconformity-Unconformity that separates underlying igneous or metamorphic rocks from overlying younger sedimentary rocks
    • F. PRINCIPE OF FOSSIL SUCCESSION
    • 1. Fossils - remains of ancient animals and plants
    • 2.Types of fossils and fossilization
    • a. Body fossils
    • i. Petrification-small internal cavities are filled with precipitated minerals
    • ii. Mold- shell is buried, then dissolved by groundwater
    • iii. Cast -mold is filled in with mineral matter
    • b. Trace fossils- tracks, trails, burrows, etc.
    • 3. Conditions favoring preservation
    • a Rapid burial
    • b. Perservable hard parts
    • 4. Principe of fossil succession
    • a. Fossil organisms succeed one another in a definite order and anytime period may be rec by its fossils
    • b. Fossils document the evolution of life on earth
    • c. Index fossils
    • i. Widespread geographically
    • ii. Lived for a short interval of geologic time
    • iii. Easily recognizable
  3. Absolute Geologic Time
    • A. PARENT AND DAUGHTER PRODUCTS OF RADIOACTIVE DECAY
    • 1.Parent-unstable isotpe
    • 2. Daughter product-result from radioactive decay
    • B.HALF LIFE-TIME IT TAKE IN YRS FOR ONE HALF OF PARENT TO DECAY TO DAUGHTER
    • C.EXAMPLES OF PARENT, DAUGHTER, AND HALF LIFE
    • 1. C14=>N14 5730+/-30 YEARS
    • 2.U235=>PB207 713 MY
    • 3.U238=>PB206 4.56 BY
  4. CORRELATION OF ROCK LAYERS
    • A. MATCHING ROCKS OF SIMILAR AGE IN DIFFERENT REGIONS
    • B. OVER LIMITED AREAS, ROCKS MAY BE MATCHED BASED ON ROCK TYPE, POSITION IN A SEQUENCE OF ROCKS.
    • C. OVER LONG DISTANCES , FOSSILS ARE USED FOR CORRELATION
  5. THE GEOLOGIC TIME SCALE
    • A. STRUCTURE OF THE TIME SCALE
    • 1. Eons- largest time units
    • a. Precambrian- reps about 88% of geo time
    • b. Phanerozic Eon- "visible life"
    • 2. Eras-eons are divided into eras
    • a.Phanerozoic Eon
    • i. Paleozoic Era- "ancient life"
    • ii. Mesozoic Era-"middle life"
    • iii. Cenozoic Era- " recent life"
    • 3. Periods-eras divided into periods
    • 4. Epochs- periods are divided into epochs
    • b. Eons
    • i. Eras
    • ii.Periods
    • iii.Epochs

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