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Test 4 [PHY-125-01]

Chapter 9 & 10 - Geologic Time & Crustal Deformation

Absolute Age where a number (yrs, min, sec) is assigned to the amount of time that has passed
Numerical Date specify the actual number of years passed since an event occurred
Relative Age where the AGE of a rock, fossil, or other geologic feature is measured RELATIVE TO ANOTHER FEATURE
Relative Dating method used by geologists to determine the general SEQUENCE of geologic events from OLDEST TO YOUNGEST
Law of Superposition [Stratigraphic Principles] in an UNDEFORMED SEQUENCE of sedimentary rocks, each bed is older than the one above and younger than the one below [●YOUNG↓ ●OLD↓ ●OLDER]
Principle of Original Horizontality [Stratigraphic Principles]  layers of sediment are generally deposited in a horizontal position  rock layers that are flat have not been disturbed
Principle of Cross-Cutting [Stratigraphic Principles]  a rock unit must always be OLDER than any feature that cuts or disrupts it  features include: faults, igneous intrusions, folding, tilting
Principle of Inclusions [Stratigraphic Principles]  a piece of rock that is ENCLOSED within another rock  a rock containing an inclusion is always YOUNGER
Conformable Layers layers of rock that have been deposited WITHOUT INTERRUPTION
Unconformity BREAKS in the rock record
Formation for the most basic rock division, constitutes a rock unit produced by UNIFORM or UNIFORMLY ALTERNATING CONDITIONS
How do unconformities form?  Long periods of NON-DEPOSITION  EROSION of material
Angular Unconformity [Unconformity] TILTED or folded SEDIMENTARY rocks are OVERLAIN by FLAT-lying rocks ̷̷͞͞͞͞ ̷̷͞͞
Disconformity [Unconformity]  strata on either side of the unconformity are parallel  more difficult to identify
Nonconformity [Unconformity] older METAMORPHIC or intrusive IGNEOUS rocks are OVERLAIN by younger SEDIMENTARY strata
Fossil traces or remains of prehistoric life preserved in rock that are important inclusions in sediment and sedimentary rocks
Criteria for fossil preservation  Rapid BURIAL  Possession of HARD PARTS (skeletons)
Petrified (permineralization) [Fossilization]  "turned into stone"  the small internal cavities and pores of an organism are filled with precipitated matter
Mold/Cast [Fossilization]  shell or other structure is buried in sediment and then dissolved by ground water  the fossil only reflects the shape and surface marking of the organism and does not reveal any information regarding its internal structure
Carbonization [Fossilization] preserving leaves and delicate animal forms that leaves behind a thin residue of an element
Impression [Carbonization: Fossilization] if film of carbon is lost a replica of the surface may still show details
Amber [Fossilization] preserving insects
Replacement [Fossilization]  cell walls and other solid materials are removed and replaced with mineral matter  microscopic detail can be preserved
Track [Trace Fossil: Fossilization] footprints made in soft sediment and later lithified
Burrows [Trace Fossil: Fossilization]  TUBES in sediment, wood, and rock made by an animal  holes may later fill with mineral water
Coprolites [Trace Fossil: Fossilization] fossil DUNG and STOMACH CONTENTS can provide information about food habits
Gastroliths [Trace Fossil: Fossilization] highly polished STOMACH STONES used in grinding food by some extinct
Radioactive Decay the SPONTANEOUS changes in the structure of atomic NUCLEI occur due to INSTABILITY in binding forces in nucleus
Alpha Decay [Radioactive Decay] occurs when the NUCLEUS is TOO LARGE to be stable  EMMISION of 2 protons and 2 neutrons (an alpha particle which is, in fact, a He nucleus) ● Mass number is REDUCED by 4 ◊ atomic number is REDUCED by 2
Beta Decay [Radioactive Decay] occurs when there are TOO MANY NEUTRONS relative to the number of protons  An electron (beta particle) is EJECTED from the nucleus ● Mass number remains UNCHANGED ◊ atomic number INCREASES by 1
Electron Capture [Radioactive Decay] occurs when there are TOO MANY PROTONS relative to the number of neutrons  An electron is CAPTURED by the nucleus and COMBINES with a proton to form a neutron ● Mass number remains UNCHANGED ◊ atomic number DECREASES by 1
Correlation Process investigative process by which geologists ID and MATCH sedimentary strata and other rocks of the SAME AGES of DIFFERENT AREAS
The Principle of Fossil Succession [Correlation Process] fossil organisms succeed one another in a DEFINITE and DETERMINABLE ORDER, therefore any TIME period can be RECOGNIZED by its fossils
What is the age of the Earth? 4.5 BILLION years
Divisions of Geologic Time [Decreasing Order] Eon -> Era -> Period -> Epoch
Where does C-14 come from? Continuously produced in the UPPER ATMOSPHERE as a consequence of COSMIC-RAY BOMBARDMENT
Precambrian  88% of Earth History  the vast amount of time that preceded the Paleozoic Era
Radiometric Dating geologists use this technique to determine the age (a NUMERICAL age) of a rock
Atomic Number  element's identifying number  equal to the # of PROTONS (or electrons in an electrically neutral atom)
Force tends to put stationary objects in motion or changes the motions of moving objects
Stress term that structural geologists use to describe the forces that deform rock
Compressional stress  differential stress that SQUEEZES and SHORTENS a rock mass  crust is SHORTENED and THICKENED, producing MOUNTAIN terrain
Tensional Stress  pulls APART or ELONGATES a rock unit  STRETCHES and LENGTHENES rock bodies in upper crust by displacement along faults  displacement at depth by DUCTILE FLOW
Shear Stress  involves movement of one part of a rock body PAST another  can occur along FOLIATION SURFACES and microscopic features  can occur along LARGE SEGMENTS of crust
Differential Stress [ ≠ ] stress applied UNEQUALLY in different directions
Confining Stress rocks deeply buried are held together by the immense pressure and tend to flow rather than fracture
Compressional Stress : Tectonic Environment CONVERGENT Plate Boundaries
Tensional Stress: Tectonic Environment DIVERGENT Plate Boundaries
Shear Stress: Tectonic Environment TRANSFORM Fault Boundaries
Ductile Deformation  BEND  once the elastic limit (strength) of a rock is exceeded, SHAPE IS CHANGED  does NOT fracture  type of solid-state flow  some chemical bonds are broken, WHILE OTHERS FORM
Examples of Ductile Deformation  Copper penny run over by a train  Modeling clay  Taffy  Beeswax
Brittle Deformation  BREAK  once the elastic limit (strength) of rock is exceeded, the rock BREAKS INTO PIECES  chemical bonds are broken
Examples of Brittle Deformation  Chalk dropped on hard surface  Glass objects  Wooden pencils  China plates  Bones
How do rocks at the earth’s surface behave? [Ductilely or Brittlely]  BRITTLE  Where temperatures are LOW rocks behave in a brittle manner and FRACTURE
How do rocks deep in the earth behave? [Ductilely or Brittlely]  DUCTILE  Where temperatures are HIGH rocks behave in a ductile manner and FLOW
What are strike and dip? Strike and dip are measurements used to determine orientation (attitude) of rock layer or fault surfaces
Strike  TREND  compass direction of the line produced by the INTERSECTION of an inclined rock layer of fault with a horizontal plane
Dip  INCLINATION  the ANGLE of inclination of the surface of a rock unit or fault measured from a horizontal plane
Anticline [ ↑ ᴖ ]  UP-folded, or arched, sedimentary rock layers  oldest rock at the CENTER, youngest rock draped over them at the top
Syncline [ ↓ ᴗ ]  DOWN-folded sedimentary rock layers  oldest rock on the OUTSIDE, youngest rock in the center
Monocline [__ᴦ--]  large, STEP-LIKE folds in otherwise horizontal sedimentary strata  oldest rock is on BOTTOM, youngest rock is on top
Dome  UP-warping produces a circular or slightly elongated structure  oldest rocks of eroded dome in CENTER, youngest rock found on the outer part
Basin  DOWN-warping produces a circular or slightly elongated structure  oldest rocks found on the OUTER part, youngest rock found near the center
How do domes form?  Domes can form by magma intrusion - Upward migration of salt formations produce salt domes - Black Hills dome formed by up-warping
How do basins form?  A few structural basins are result of giant asteroid impacts - Michigan and Illinois basins formed by large accumulations of sediment which caused crust to subside
Limb [Part of a Fold] 2 sides of a fold
Axial Plane [Part of a Fold] imaginary surface dividing fold
Hinge Line [Part of a Fold] line drawn along maximum curvature of the fold
Plunge [Part of a Fold] hinge line is at an angle
Reverse Fault dip-slip faults where HANGING WALL moves UP relative to footwall
Normal Fault  dip-slip fault where HANGING WALL moves DOWN relative to footwall  lengthening of crust due to tensional forces
Strike-Slip Fault  displacement is mainly horizontal and parallel to strike of fault surface  classified as right and left lateral
Thrust Fault reverse faults having dips less than 45°, so overlying block moves nearly horizontally over the underlying block
Hanging Wall Block rock surface immediately ABOVE fault
Footwall Block rock surface immediately BELOW fault
Created by: KierstyN_O13