Midterm Flashcards
what is geology?
the study of the Earth
what are objective facts/observations?
true for everyone. science is based on this. an example is “the fault is 5.6 “ long”
what are subjective facts/observations?
true for some but not for all. based upon opinion
what is a hypothesis?
a tentative, testable explanation of a observation
what is a theory?
best explanation of a natural phenomenon that is supported by a wide range of data. “all data agree”. all other explantations have been falsified
what is a law?
a statement or equation that simply states a natural relationship. consistent. doesn’t explain it just states.
Walter and Luis Alvarez were examining a mysterious layer of clay that was _____ . They hypothesized that this layer formed as the result of _______
rich in iridium; an asteroid impact on Earth
what is the definition of a mineral?
inorganic crystals that occur in nature. they are the building blocks of most rocks. naturally occurring, inorganic, solid, well defined chemistry (that can vary within limits) and a crystalline structure
what is the definition of a rock?
aggregates (collections) of minerals, glass, or pieces of rock. rocks are collection of mineral crystals.
what is a igneous rock?
cooled from a liquid (melt). results when a lava cools. ex. granite
what is a sedimentary rock?
debris cemented from preexisting rock
what is a metamorphic rock?
rock altered by pressure and temperature. form when a pre-existing rock is exposed to higher pressure and/or temperature.
what are the majority of rocks on Earth considered as and why?
silicates; made of minerals rich in silicon and oxygen. bounded together as SiO4-4. many of these rocks are igneous rocks
what are the four fundamental igneous rock chemistries?
they are based on % of silicon dioxide ; 1. felsic (highest silica %) ex. granite; 2. intermediate ex. diorite; 3. mafic ex. basalt and grabbro; 4. ultramafic (lowest silica %) ex. peridotite
Which element is the most abundant in the Earth as a whole?
Iron
what rock is the mantle composed of?
Periodotite which is a igneous rock with a ultramafic chemistry
oceanic crust characteristics?
low variation of rock types, made of magic igneous rocks - basalt and gabbro, more dense, younger (gets recycled), 3-10 km thick
continental crust characteristics?
wide variation of rock types, chemistry is felix - made of granite, less dense, older (can not be recycled), 20-70 km thick
why does behavior change?
pressure and temperature increase with depth
what is the geothermal gradient?
the rate at which the temperature changes with depth.
In general, what happens to temperature as one goes from the Earth’s surface to the Earth’s core?
temperature increases
what is the Mohorovicic Discontinuity (moho)?
a boundary between the crust and mantle
The term “lithosphere” refers to?
the outer shell of the Earth, composed of the crust and lithospheric mantle.
what are the 5 principles to the theory of plate tectonics?
- the lithosphere is broken into numerous plates; 2. these plates move on top of the underlying asthenosphere; 3. the plates move very slowly; 4. the plates interact at plate boundaries generating geologic activity; 5. the geologic activity is concentrated at plate boundaries
what are plate boundaries?
locations on Earth where tectonic plates meet/interact. defined by geologic activity
what is a continental margin?
where land meets the ocean
what is a active continental margin?
margin is associated with an active tectonic boundary. . Places where the oceanic and continental lithosphere tectonic plates meet and move relative to each other. West coast of North America
what is a passive continental margin?
margin that is NOT associated with an active tectonic boundary. The eastern coast of the North American continent is considered this.
what is a fault?
a crack/fracture in the Earth where one block of rock moves against another block of rock. ALL of the plate boundaries will have faults. how the blocks move will be different
convergent plate boundaries?
lithosphere plates move towards each other; may result in a zone of subduction or continental collision; subduction is the process by which oceanic lithosphere sinks into the mantle - subduction recycles oceanic lithosphere; Himalayas
what is the result of subduction is generated because the asthenosphere melts, why?
- subducting plates releases water; 2. water chemically reacts to the asthenosphere; 3. the asthenosphere a solid, partially melts to form magma
what are the features at subduction zones?
trench, earthquakes, and volcanic mountain chains (arcs)
what is a trench?
a location where oceanic crust bends and begins to subduct. represents convergent plate boundaries and subduction zones. they are deep and arc shaped
what kind of rock makes up the core?
Outer Core : liquid iron — the flow of liquid iron to the outer core is responsible for Earths magnetic field
Inner Core: solid iron
what is the asthenosphere?
It is a solid, but behaves in a plastic-like manner;
It is mechanically weak and moves and flows due to convection currents created by heat coming from the earth’s core; Slow, ductile movement allows the plates to move on it
List the three types of plate tectonic boundaries. Describe the relative plate motions of each. Provide an example of each.
Convergent: moves towards each other - Himalayas; Divergent: moves away from each other – Midatlantic Ridge; Transform: Slides against each other – San Andreas Fault
At what boundary is oceanic lithosphere created? At what boundary is oceanic lithosphere destroyed?
Divergent plate boundaries is where oceanic lithosphere is created by midocean ridges; Oceanic lithosphere is destroyed at convergent boundaries by subduction and subduction zones; Subduction recycles oceanic lithosphere; This creates trenches
Provide real-life examples of a subduction zone and a continental collision zone.
Southern Alaska – Pacific and Juan de Fuca plates slide beneath the North American Plate; Himalayas Mountains are continental collision
When two plates collide, what determines which plate will subduct?
The plate that is older will be colder, and that plate will subduct
What is the Wadati-Benioff Zone?
It is a zone in the upper mantle in which earthquakes occur when a lithosphere plate subducted; Earthquakes follow the subduction plate
Describe the seafloor spreading process.
- Process by which new oceanic crust is created at mid-ocean ridges, creating and widening ocean basins. Magma is generated in the asthenosphere and rises; magma rises through the mid-ocean ridge boundary and erupts; lava cools adding to each plate; new oceanic crust is created, then spreads leaving the ocean basin to expand in widt
What is a mid-ocean ridge?
Associated with and represent divergent boundaries; ridges are underwater mountain ranges; not a gap, but a series of vertical crocks in rocks
What are the two general types of transform plate boundaries? Which is more common?
Oceanic and continental – oceanic being more common
Who proposed the Continental Drift (CD) hypothesis and what did the hypothesis state?
Alfred Wegener- The hypothesis suggested that 300 to 250 million years ago all of the continents combined Pangea / all of the continents were once combined into a supercontinent
Describe how fossil evidence supported the CD hypothesis
identical fossils found on landmasses that are currently separated; Mesosaurus: freshwater reptile; lystrosaurus: land-dwelling herbivore; glossopteris: topical plant with heavy seeds. He pointed out that land dwelling animals could not have swam across the ocean
Describe how the shape of the continents supported the CD hypothesis
Wegener noted that continents seem to fit together; Using continental shelf edges make a near fit
Describe how glacial evidence supported the CD hypothesis
Wegener noted that some Permian rocks suggest that between 300 to 250 million years ago, portions of South America, Africa, Australia, and India were covered in glacial ice; This means that during the Permian the entire planet was covered in ice OR 2 continents can move and these areas were located near the South Pole
What is paleomagnetism and how is it preserved in rocks?
The study of fossil magnetism preserved in rocks; Some iron rich/bearing minerals (magnetite) in rocks (mostly igneous rocks) align to the magnetic field at the time of rock formation and it perserves
What is meant by a “normal” and “reverse” polarity?
Normal polarity: magnetic N is near geographic N
Reverse polarity: magnetic S is near geographic N
Describe how the thickness of ocean floor sediment helped support sea-floor spreading.
As time passes, sediments accumulate on the ocean floor; older crust will have a thicker layer of sediment than younger crust; at trenches, oceanic crust is very old, cold, and dense, and it begins to sink and dive back into the mantle, this process generates deeper earthquakes; Thinner sediment layers were found near mid ocean ridges showing the ridges were younger than the ocean floor
what is the lithospheric mantle?
the portion of the lithosphere within the mantle, it is solid and uppermost part of the mantle
Describe the age of the oceanic crust along a divergent plate boundary
The crust is youngest at the spreading center and gets older as you move away from the divergent boundary
what is a mantle plum?
hot rock that rises from the core-mantle boundary. Stationary
what is a hotspot?
volcanic feature above mantle plume (on the crust)
How do scientists use hot spots to determine the speed and direction of a tectonic plate? How can you determine the direction in which a plate is moving using a hotspot chain?
As the tectonic plates move above a hotspot, they form a chain of volcanoes. The older the volcanoes the way the plate moves.
Whats an example of a oceanic hot spot and a continental hotspot?
oceanic: hawaiian islands
continental: yellowstone wyoming
What is the difference between absolute and relative plate motions
Absolute plate motions: the motion of one plate relative to a fixed reference system
Relative plate motions: the motion of one tectonic plate relative to another
What is a crystalline structure?
Is a 3D arrangement of atoms that repeats itself. Influences many of the mineral’s properties. If it doesn’t have an arrangement of atoms, then it is not a mineral.
What is a polymorph?
A polymorph is a mineral that has the same chemical formula but a different crystalline structure.
Examples: graphite, diamond
Discuss the 3 ways minerals are created in nature. Which one occurs in sedimentary, metamorphic, and igneous environments?
Solidification from a melt – Igneous
Precipitation from a solution – Sedimentary
Solid state diffusion: ions migrate through minerals while in a solid state. - Metamorphic
How are minerals classified? What are some mineral classes?
Minerals are classified based upon their anion or anionic group. Sulfides, oxides, carbonates, silicates
What are grains and what is grain size?
Grain size is the measurable size of the grain (crystal or clast)
