GEO Final Exam

How do geologists examine the world?

Repeatable observations and testable ideas

How does a hypothesis differ from a theory?

A hypothesis is a suggested explanation, while a theory is a well-substantiated UNIFYING EXPLANATION for a set of proven hypotheses

What is the theory of uniformitarianism?

The present is the key to the past — processes we observe today should also be preserved in the rock record

How old is the Earth?

4.56 billion years old

How do we determine the age of the Earth?

Meteorites — we know that the age of meteorites should be the same age of the Earth

What is the structure of the Earth?

Inner core — solid iron

Outer core — liquid iron

Mantle — solid but moves a bit

Crust — very thin, 50% oxygen

What is the lithosphere?

Solid, rigid outermost part of the Earth (both crust and uppermost part of the mantle)

Which layer of the Earth is the least dense?

crust

Which layer of Earth is liquid?

outer core

Which solid layer of the Earth undergoes convection?

mantle

What is the definition of a plate?

The crust and upper part of the mantle (lithosphere)

What is the asthenosphere?

upper layer of the mantle that is partially melted

What is the evidence for plate tectonics and continental drift?

* Mountain belts that are mirror images on either side of the Atlantic
* Fossils occur in belts that match up
* Paleo-environments match on either side of the Atlantic (climates occur in latitudinal bands)
* Glacial occurrences in the southern hemisphere up to India
* Occurrence of very old rocks (> 1 billion years old)

What is the driving force of plate tectonics?

New sea floor emerging along the cracks in mid-ocean ridges

How did continental drift become a theory?

Technological advances during WWII found underwater mountains (mid-ocean ridges with cracks down center)

Tested the magnetic field of the seafloor (Earth can shift polarity) indicating that the pattern and ridge mirrors on either side of the mid-ocean ridge

What layer do plates move on?

asthenosphere

What drives plate motion?

convection in the asthenosphere

What are the three types of plate boundaries?

Divergent — plates move apart

Convergent — plates move together

Transform — plates slide past each other

What occurs at divergent boundaries and how do we recognize them?

New crust emerges

Rift valleys, small shallow earthquakes, age of crust around it

What occurs at convergent boundaries and how do we recognize them?

One plate slides below the other, oceanic crust is thinner and gets recycled back down the mantle

Earthquakes are deeper moving away from plate boundary on one side of the plate (the side sliding down)

Oceanic trench, volcanic island arc, folded mountains

What is subduction?

The process of oceanic crust moving below the other plate and being recycled

What type of stress occurs at convergent plate boundaries?

Compressional stress

What does subduction do?

Destroys oceanic crust and creates earthquakes and volcanoes

What occurs at a transform boundary and what are the characteristics?

Plates slide past each other (result of shear stress)

Crust is preserved, shallow earthquakes, horizontal motion dominates

Offset streams

What is a hot spot?

Plume of hot material that rises up from the core-mantle boundary (independent of plate tectonics)

How much do plates move a year?

About a centimeter

What type of stress occurs at which boundary?

Divergent — tensional

Convergent — compressional

Transform — shear

How do we calculate the rate of motion?

rate \= distance/time

What is an isotope?

Atoms of the same element that have different numbers of neutrons

What is a cation? What is an anion?

Cation — lose one or more electrons (left side of periodic table)

Anion — elements that gain electrons (right side of periodic table)

What is an ionic bond?

Weak bond, donate an electron (ex: Halite (salt))

What is a covalent bond?

Two atoms share outer electrons — strong bond

What is a metallic bond?

Occurs with metals — overlap of e- cloud that allows high conductivity, high density, weak bond

What are the most common elements in each layer of the Earth?

Oxygen, silica, aluminum, iron, calcite, potassium, magnesium, and sodium

What are native elements?

Native metals plus sulfur or carbon, occur as minerals

What are oxides and hydroxides?

Cation plus oxygen or OH

What are halides?

Cation + halogen

What are sulfides?

Cation + sulfur

What are sulfates?

cation + SO4

What are carbonates?

Cation + CO3

What are silicates?

Silicon, SiO

What constitutes a mineral?

* naturally occurring
* solid
* highly ordered atomic arrangement
* definite chemical composition
* inorganic

What are the physical properties used to identify minerals?

* form
* hardness
* cleavage/fracture
* reaction to HCl
* magnetism
* transparency
* luster
* color
* smell/taste/feel

How are igneous rocks formed?

Cool from molten rock

What is the rock cycle?

1. existing rock melts to form liquid rock (magma)
2. Magma cools to form igneous rock (crystallization)

What is the difference between intrusive and extrusive rocks?

Intrusive are underground (magma), extrusive are above ground (lava)

What are macroscopic igneous rock formations?

Simple structures (don't share oxygen) and complex (maximum sharing of oxygen)

More silica = more complicated

What factors cause rocks to melt?

Everything doesn't melt at once, the rocks with lower melting temp melt first (lower silica, higher melting temp)

Raise the temperature, lower the pressure, or adding water can all cause rocks to melt

What causes smaller grain size versus larger?

The quicker is cools, the smaller the grain size

What is a batholith and how does it form?

Large bodies of plutonic rocks that probably form when the magma melts the rock above it and it drops into the magma chamber

What can the color of igneous rocks tell us?

Light colored — closer to surface, made of silica

What are the types of volcanic eruptions?

More silica = cooler = more complicated bonds = more sticky = more explosive

Less silica (basaltic) = hotter = more fluid = effusive (not explosive)

Where is basalt produced?

Under water (divergent boundaries), along fissures, hot spots (shield volcanoes)

What are the traits of shield volcanoes?

Gentle sides, huge, non-explosive eruptions, long durations of activity

What are the traits of statovolcanoes (composite volcanoes)?

Mostly a desire, pyroclastic deposits, intermediate steepness, smaller, highly explosive, intermittent eruptions over long time span (on convergent boundaries)

How can we predict eruptions?

Eruptive history - from volcanic deposits

Earthquakes - harmonic tremor - magma moving underground

Ground tilting - magma nearing surface

Temperature of ground or groundwater increasing (magma close to surface)

Gas - emitted from ground (magma close to surface)

What are some volcanic hazards?

Pyroclastic flows

Lahar — mud flow

Releasing toxic gases

Climate change — H2SO4 can remain in atmosphere for months or years

Volcanic bombs — solidifies almost immediately in atmosphere

Tsunamis

What gases do volcanoes primarily release?

H20, CO2, SO2 (sulfur oxide)

What determines the type of lava/magma?

The amount of silica in the lava/magma

What type of magma/lava is associated with which plate boundary type?

Basaltic lava — divergent, hot spots

Andesite/silica lava — convergent

What are some types of faults/their qualities?

Strike-slip fault — vertical (or nearly vertical) fractures where the blocks have mostly moved horizontally

Thrust fault — compressive stress shortens Earth's crust, forces Earth up (mountains)

What is transpression?

Restraining bends where rock volumes pile w/ combo of strike-slip and reverse motion

What is transtension?

At releasing bends where rock volumes move away from each other, strike-slip and normal motion

What are the types of weathering?

1. Physical (Mechanical)
2. Chemical
3. Both types of weathering happen simultaneously!!\*

What are the types of mechanical weathering?

* breaking of rocks into smaller points at joints (cracks)
* Sheeting - planar fractures parallel to surface (caused by decrease in pressure)
* Thermal expansion (exfoliation) - heating up during the day, cooling at night
* Freeze-thaw - increase in volume as water freezes
* Water abrasion - rounded shapes in river
* Wind abrasion - glassy surfaces, sharp angles
* Glacial abrasion — polish rocks

What are the types of chemical weathering?

* Simple dissolution - some minerals dissolve in water
* Carbonation - 1. CO2 + H20 —> H2CO3 2. H2CO3 + CaCO3 —> Ca(HCO3)2 + H2O


* Oxidation - iron loses an electron - Fe2 —> Fe3 + e-
* Reduction - iron gains an electron - Fe3 + e- —> Fe2
* (OIL RIG - Oxidation is loss, Reduction is gain)
* Hydrolysis - silicate weathering can pull carbon dioxide out of atmosphere

How does silicate structure and chemical composition relate to chemical weathering?

Traits that indicate the mineral formed deeper mean it will weather first — high temperature crystallization, more iron/magnesium, isolated silicate tetrahedra structure

Which type of rocks weather more slowly: felsic or mafic?

Felsic

How does the climate impact what type of weathering will occur?

Strong physical weathering will occur in colder/dryer climates, while strong chemical weathering will occur in warmer/wetter climates

How are sedimentary rocks formed?

Layers of sediment are cemented together over time.

How do rivers form sedimentary rocks?

Erode bedrock and deposit sediments

What type of energy/deposits do mountain streams create?

High energy, large boulders deposited

What type of energy/deposits do flood plain rivers create?

Moderate energy and more deposition (travel more smoothly), deposits sands, muds and cobbles

What types of sediments are deposited?

Shales (mud cobbled together) sandstone and conglomerates

What type of energy/deposition do deltas have?

Almost no energy, drops all sediments it carries

What is an alluvial fan deposition?

Forms along mountain fronts, stream water sinks into the ground

What are the two types of sedimentary rocks?

Clastic (particles cemented together) and chemical

What is a loess and how does it form?

Wind blown dust from ice age that forms in layers

What type of rocks forms in coral reefs?

Limestone (calcium carbonate)

What are the three evaporates?

Halite, gypsum, borate

How do metamorphic rocks form?

heat and pressure

What are the two types of pressure that create metamorphic rocks?

Confining pressure (squeezing from all sides) and directed pressure (squeezing in one direction)

What are the types of metamorphism?

Contact - lava bakes mudstone

Regional - increased temp and pressure in convergent plate

What are the metamorphic textures?

Foliated (visible layering) and non-foliated

What are three non-foliated rocks?

Marble, quartzite, eclogite

What does an increase in metamorphism mean in crystal size and coarseness?

Increase intensity \= increase crystal size \= increase coarseness

Describe each of the following rocks:

Slate

Phyllite

Schist

Gneiss

Mignatite

Slate - very flat cleavage

Phyllite - wavy surface

Schist - lots of muscovite and biotite

Gneiss - bands of felsic and mafic minerals

Mignatite - part of rock has melted and recrystallized

What do we call the idea that geologic processes that are happening today have operated in the past?

Uniformitarianism

Alfred Wigner is know for what geologic hypothesis?

Continental drift

What property of a clastic sedimentary rock indicates the distance its clasts were transported before deposition?

Grain size

Which rock commonly forms form evaporation in a desert lake?

Halite

Which of the following rocks are deposited in a river channel?

A. Breccia

B. Organic rich shales and mudstones

C. Sandstones and conglomerates

D. Halite

C

Which of the following metamorphic rocks is characterized by a silvery sheen and slightly wrinkled surface?

A. Schist

B. Marble

C. Phyllite

D. Shale

C

Basalt is:

A. More viscous than rhyolite

B. Has a higher silica content than rhyolite

C. is generally associated with divergent plate boundaries

D. Is typically explosive

C

Which mineral can you scratch with your fingernail?

Gypsum

Which layer of the Earth allows plates to move because it is partially molten?

Asthenosphere

The nucleus of an atom contains:

neutrons and protons

What are four volcanic hazards?

Tsunamis, gases, climate change, pyroclastic material

Which of the following minerals crystallize at the highest temperatures in cooling magma?

A. Quartz and muscovite

B. Na-rich plagioclase and amphibole

C. Ca-rich plagioclase and olivine

D. Chert and k-feldspar

C

Which type of rock is most typical of continental crust?

Granite