Geology

• Plate Tectonics: The Unifying Theory
• Plate Tectonics states that Earth’s surface is composed of a few large, thick plates that move slowly and change in size.
• Plate boundaries are where plates move away, toward, or past each other through intense geologic activity.
• Plate Tectonics developed from the continental drift and seafloor spreading hypotheses.
• The early case for Continental Drift was the puzzle-piece fit of coastlines of Africa and South America.
• Layer 3 of the oceanic crust is represented by sill-like gabbro intrusions, which are not directly sampled.
• The age of the sea floor is less than 200 million years old.
• Continents preserve rocks up to 4 billion years old.
• The explanation of the young age and formation mechanisms of oceanic crust is a crucial part of the Theory of Plate Tectonics.
• Ophiolites are composed of Layers 1 to 3 overlying ultramafic rock.
• Layer 2 of the oceanic crust is composed of pillow basalt overlying basaltic dikes, which are extensively sampled.
• Ophiolites are rock sequences in mountain chains on land that are thought to represent slivers of ocean crust and uppermost mantle.
• Alfred Wegener, a noted scientist, stated that Africa, South America, India, Antarctica, and Australia have almost identical late Paleozoic rocks and fossils.
• Pangaea is a supercontinent proposed by Wegener.
• Laurasia is a northern supercontinent containing North America and Asia (excluding India).
• Gondwanaland is a southern supercontinent containing South America, Africa, India, Antarctica, and Australia.
• Glaciation patterns were evident on the southern continents (Gondwanaland) during the Late Paleozoic.
• Coal beds were deposited in the northern continents from swampy, probably warm environments (Laurasia) during the Late Paleozoic.
• Paleoclimate belts suggest potential evidence for polar wandering.
• Polar Wandering is the apparent movement of the poles.
• The mechanism proposed by Wegener, that the continents plowed through the oceans propelled by centrifugal forces from the Earth’s rotation and gravitational forces that cause the tides, was not accepted by most geologists in the northern hemisphere.
• Paleomagnetism is the study of ancient magnetic fields.
• The mineral magnetite becomes magnetized in cooling lava once its temperature drops below the Curie Point.
• Paleomagnetism uses mineral magnetic properties to determine direction and distance to the magnetic pole when rocks formed.
• Magnetic reversals are times when the poles of Earth’s magnetic field switch, recorded in magnetic minerals, and occurred many times; timing appears chaotic.
• Elastic deformation is when deformed materials return to original shape after stress is removed, while elastic limit is the point beyond which the rock will not return to its original shape and is permanently deformed.
• Gravity meters detect tiny changes in gravity at Earth’s surface related to total mass beneath any given point.
• Magnetic anomalies are local increases or decreases in the Earth’s magnetic field strength, with positive and negative magnetic anomalies representing larger and smaller than average local magnetic field strengths, respectively.
• Magnetometers are instruments used to measure local magnetic field strength, and can detect metallic ore deposits, igneous rocks, and thick layers of non-magnetic sediments beneath Earth’s surface.
• Paleomagnetism is the study of ancient magnetic fields in rocks, allowing reconstruction of plate motions over time.
• Heat flow is the gradual loss of heat through Earth’s surface, with major heat sources including original heat and radioactive decay, locally higher where magma is near surface, and has the same magnitude, but with different sources, in the oceanic and continental crust.
• Geologic structures are dynamically-produced patterns or arrangements of rock or sediment that result from, and give information about, forces within the Earth.
• Ductile deformation is when a material is bent and will not return to its original shape once the stress is removed, while brittle deformation is when a material is bent and will not return to its original shape once the stress is removed.
• Rock structures are determined on the ground by geologists observing rock outcrops, places where bedrock is exposed at the surface.
• Geologic Maps are a map which uses standardized symbols and patterns to represent rock types and structures.
• Tilted beds, joints, and faults are planar features whose orientation is described by their strike and dip.
• Rise of crust after ice sheet removal is called crustal rebound.
• A magnetic field is a region of magnetic force with north and south magnetic poles, recorded by magnetic minerals in igneous rocks as they cool below their Curie Point.
• Geothermal gradient is the temperature increase with depth into the Earth, tapering off sharply beneath lithosphere, due to steady pressure increase with depth, increased temperatures produce little melt except in the outer core.
• Gravity is slightly higher over dense materials and slightly lower over less dense materials.