Summa 1 Flashcards
occurs at or near Earth’s surface and are powered by energy from the sun
external processes
It is a basic part of the rock cycle because they are responsible for transforming solid rock into sediment.
external processes
the physical breakdown (disintegration) and chemical alteration (decomposition) of rocks to form soil or loose particles at or near Earth’s surface.
weathering
physical breakdown
disintegration
chemical alteration
decomposition
_____ causes deterioration of building materials. It also weakens rocks, a great concern when weathered rocks are used for foundation.
Weathering
types of weathering
mechanical(physical) and chemical
accomplished by physical forces that break rock into smaller and smaller pieces without changing the rock’s mineral composition
Mechanical(Physical) Weathering
involves breaking down rock components and internal structure and forming new compounds.
chemical weathering
5 processes of physical weathering
unloading, frost wedging, salt crystal growth, thermal expansion and contraction, biological activity
Upon removal of overburden (unloading), the elastic component of rock deformation is recovered and the rock expands, e.g. the overlying rocks are eroded or rocks are removed from a quarry
unloading
The expansion caused by unloading may be sufficient to fracture the rock. Such naturally formed cracks are called,
joints
The unloading of large plutons may split into sheets that are parallel to the mountain face, a process called
exfoliation/sheeting
It is also known as ______ if the expansion occurs in granite to form rock slabs.
sheeting
Liquid water expands by __% in volume when freezing.
9
Liquid water expands by 9% in volume when freezing. So one of the most effective mechanical weathering processes is the wedging action of repeated cycles of freezing and thawing of water in rock fractures.
frost wedging/ice wedging
Liquid water expands by 9% in volume when freezing. So one of the most effective mechanical weathering processes is the wedging action of repeated cycles of ______ ____ _____ of water in rock fractures.
freezing and thawing
Conditions for ________ include moisture, rock fracture or weakness planes, and temperature fluctuation around the freezing point.
frost wedging
Conditions for frost wedging include ____, _______, and ______ around the freezing point.
moisture, rock fracture or weakness planes, temperature fluctuation
A product of frost wedging is _______ made of angular rock pieces piling up at the base of steep cliffs.
talus slope
It begins when sea spray from breaking waves or salty groundwater penetrates crevices and pore spaces in rock. As this water evaporates, salt crystals form. As these crystals grow larger, they weaken the rock by pushing apart the surrounding grains or enlarging tiny cracks.
salt crystal growth
As temperature changes, not all parts of a rock or all its minerals expand or contract by the same amount. So when rocks are heated or cooled, the mineral grains are subjected to differential stresses.
thermal expansion and contraction
Accomplished by the activities of organisms, including plants, burrowing animals, and humans. Plant roots in search of minerals and water grow into fractures, and as the roots grow, they wedge the rock apart. Burrowing animals further break down the rock by moving fresh material to the surface, where physical and chemical processes can more effectively attack it. Decaying organisms also produce acids, which contribute to chemical weathering.
biological activity
Organisms such as lichen and algae often live on bare rock and extract minerals from the rock by ion-exchange mechanisms.
chemical weathering
This bio-chemical weathering process leaches minerals from the rock causing it to weaken and breakdown.
chemical weathering
The decaying of plant materials can also produce acidic compounds which dissolve the exposed rock.
chemical weathering
The presence of organisms growing, expanding, or moving across the surface of the rock also exerts a small amount of abrasion and pressure that gradually cause the ________ of the rock as the organisms extract various minerals.
mechanical weathering
The most common form of biological weathering is when plant roots penetrate into cracks and crevices of rocks and cause the rock to split or break into smaller particles through mechanical weathering.
plant roots
Although, this process is gradual, it can be fairly effective at breaking apart rocks that may already have a pre-existing weaknesses such as fractures, faults, or joints.
plant roots
Burrowing, tunneling, and acid-secreting organisms are another form of biological weathering that chemically or mechanically contribute to weathering
organism activity
Some animals may burrow or tunnel into rocks or cracks in rocks and cause the rock to break down and disintegrate. Small animals, worms, termites, and other insects, often contribute to this form of biological weathering.
organism activity
Some organisms, such as snails, barnacles, or limpets, attach themselves to rocks and secrete acid acids that chemically dissolve the rock surface.
organism activity ; chemical weathering
When rock comes in contact with components of the surface and atmosphere (water, oxygen, carbon dioxide), __________ occur that alter and destroy minerals of the rock. Water is the most important agent of chemical weathering.
chemical reactions
______ is the most important agent of chemical weathering.
water
______ weathering occurs at the surfaces of rocks, thus, the greater the surface area, the more intense the weathering. Thus the breaking of rock into smaller pieces by ______ weathering greatly accelerates _____ weathering.
Chemical; mechanical; chemical
Water is an excellent solvent, capable of dissolving many chemical compounds. This is the result of polar nature of water molecules: the oxygen end has a small negative charge, the hydrogen end has a small positive charge.
dissolution
In addition, CO2 in the atmosphere and soils reacts with water to produce ________
carbonic acid
H2O + CO2 ->
H2CO3 (carbonic acid)
CaCO³ + H²CO³ ->
Ca² + CO² + H²O
________ is the reaction of acidic solutions with silicates (the most common mineral group). For example, the weathering of K-feldspar of granite is as follows
hydrolysis
2KAlSi3O8
K-feldspar
2(H+ + HCO3-) + H2O
carbonic acid
Al2Si2O5(OH)4
kaolinite
2K+ + 2HCO3-
in solution
4SiO2
silica
A product of the chemical breakdown of K-feldspar is clay mineral, ______, which is very stable at the surface. Consequently, clay minerals make up high percentage of soils.
kaolinite
when oxygen (dissolved in the water) combines with iron to form iron oxide
oxidation
Iron-rich minerals is subject to ,
oxidation
4Fe + 3O2 ->
2Fe2O3 (hematite)
Some minerals are more susceptible to chemical weathering than others. For silicates, the order of weathering (Goldrich’s mineral stability series) is the same as the order of crystallization (so called Bowen’s reaction series).
rock characteristics
_______ is perhaps the single most important factor influencing weathering.
Climate
______ and _____ have strong influences on both mechanical weathering (e.g. frost wedging) and chemical weathering. Thus, chemical weathering is ineffective in polar regions or arid regions because of the lack of free water.
Temperature ; moisture
Climate controls the type and extent of weathering because of the combined effects of _______.
precipitation, temperature and vegetation
_______ is most pronounced in the _____, where these factors reach maximum: and weathering is minimum in deserts and polar region, where these factors are minimal.
Weathering ; tropics
Weathering is most pronounced in the tropics, where these factors reach maximum: and weathering is minimum in ____ and _____, where these factors are _____.
deserts; polar region; minimal
geological processes that is occurring or formed beneath the Earth’s surface
endogenic processes
______ is the gradual addition of new material. When the Earth first accreted, it probably wasn’t spherical.
Accretion
Accretion is the gradual addition of new material. When the Earth first accreted, it probably wasn’t spherical. ____ was generated and retained.
HEAT
sources of internal heat:
accretionary heat, radioactive decay, partial melting and origin og the magma
_____ attracts planetesimals to the proto-earth
Gravity
______ accelerate on their journey, gaining kinetic energy
Planetesimals
𝐾𝐸=
1/2𝑚𝑣^2
Planetesimals strike the proto-earth at ______
high speed
Their kinetic energy is converted to ___________
thermal energy (heat)
Soon after it formed, each planet was partially heated by countless _______ crashing into it. This was material left over from the formation of the solar system, and the kinetic energy of the impactors was transformed into _______ when they collided.
planetesimals ; thermal energy
This explains why we find _____ from undifferentiated asteroids that have been thermally altered — the asteroid they came from was not large enough to completely ___ but impacts melted portions of the surface.
meteorites ; melt
This explains why we find _______ from undifferentiated asteroids that have been thermally altered — the asteroid they came from was not large enough to completely melt but impacts melted portions of the surface.
meteorites;
The natural disintegration of certain isotopes to form new nuclei
radioactive decay
Time for nuclei to decay given by a “half-life”
radioactive decay
_____ is an important source of the Earth’s internal heat
Radioactive decay
___ is the ultimate source of the energy that drives geological activity on any planet
Heat
The ____ heat of the Earth, fueled by ___, is the “______” that drives the geological activity of the planet
internal; radioactivity; engine
___, for example, erupt because the ___heat inside the Earth melts rock and creates supplies of molten magma;
Volcanoes; heat
the magma is less ____ than surrounding rock, so it tends to ___ to the surface.
dense; rise
_____ are also caused by pressure associated with the movements of molten rock.
Earthquakes
Without radioactivity, the Earth’s _____ would have cooled long ago
interior
Without radioactivity, the Earth’s interior would have cooled long ago. Volcanoes would be extinct, and there would be no earthquakes. Earth would be geologically _____.
dead
______ is one of the main sources of heat inside the Earth.
Radioactivity
26Al ® 26Mg + Energy + … (t1/2 = 0.72 x 106 yrs)
129I ® 129Xe + Energy + … (t1/2 = 16 x 106 yrs)
short-lived isotopes
40K ® 40Ar + Energy + … (t1/2 = 1270 x 106 yrs)
232Th (t1/2 = 1400 x 106 yrs)
235U (t1/2 = 704 x 106 yrs)
238U (t1/2 = 4470 x 106 yrs)
long-lived isotopes
_____ is a measure of particles’ speed, so increased _____ results in a higher temperature.
Temperature ; motion
Radioactive material is therefore an _____, and it _____ the interior of the planet in which it’s trapped.
energy source; heats
Evidence from the study of earthquake waves has shown that Earth’s crust and mantle are composed primarily of ____, not molten, rock.
solid
Recall that igneous rocks are composed of a mixture of _____. Since these minerals have different ______, igneous rocks tend to melt over a temperature range of at least ___°C.
minerals; melting points; 200
As rock begins to melt, the minerals with the lowest melting temperatures are the first to melt. If melting continues, minerals with higher melting points begin to melt, and the composition of the melt steadily approaches the overall composition of the rock from which it was derived.
partial melting
As rock begins to melt, the minerals with the _____ melting temperatures are the first to melt.
lowest
Most often, however, melting is not complete. The incomplete melting of rocks is known as _______, a process that produces most magma.
partial melting
Also, because the molten material is less dense that the remaining solids, when enough of the melt collects, it ______ toward Earth’s surface.
rises
Although the rate of temperature change varies considerably from place to place, it averages about 25°C per kilometer in the upper crust. This increase in temperature with depth is known as the geothermal gradient.
generating magma from solid rock
Although the rate of temperature change varies considerably from place to place, it averages about ___°C per kilometer in the upper crust. This increase in temperature with depth is known as the _________.
25; geothermal gradient
When a typical geothermal gradient is compared to the melting point curve for the mantle rock peridotite, the temperature at which peridotite melts is higher than the geothermal gradient. Thus, under normal conditions, the mantle is solid. However, tectonic processes exist that trigger melting by reducing the melting point (temperature) of mantle rock.
generating magma from solid rock
When a typical geothermal gradient is compared to the melting point curve for the mantle rock ______, the temperature at which peridotite melts is _____ than the geothermal gradient.
peridotite; higher
Thus, under normal conditions, the mantle is _____. However, tectonic processes exist that trigger melting by reducing the ____ (temperature) of mantle rock.
solid; melting point
Pressure which also increases with depth influences the melting temperatures of rocks.
decrease in melting / decompression melting
_____ which also increases with depth influences the melting temperatures of rocks.
Pressure
Melting, which is accompanied by an increase in ____, occurs at progressively higher temperatures with increased depth.
volume
Melting, which is accompanied by an increase in volume, occurs at progressively higher temperatures with increased depth.
decrease in melting /decompression melting
This is the result of the steady increase in confining pressure exerted by the weight of overlying rocks.
decrease in melting / decompression melting
Conversely, reducing confining pressure ____ a rock’s melting temperature. When confining pressure drops sufficiently, _______ is triggered.
lowers ; decompression melting
Water causes rock to melt at lower temperatures.
addition of water
_____ causes rock to melt at lower temperatures.
Water
The introduction of ____ to generate magma occurs mainly at ______ plate boundaries where cool slabs of oceanic lithosphere descend into the mantle
water ; convergent
At a depth of about ____ km (___ miles), the addition of water lowers the melting temperature of mantle rock sufficiently to trigger _____.
100; 60; partial melting
Partial melting of the mantle rock peridotite generates hot basaltic
magmas with temperatures that may exceed _____°C (____°F)
1250; 2300
When enough mantle-derived basaltic magma forms, it buoyantly ___ toward the surface
rises
When enough mantle-derived basaltic magma forms, it buoyantly rises toward the surface
Temperature increase(melting crustal rocks)
The hot basaltic magma may ____ the overlying crustal rocks sufficiently to generate a ____, silica-rich magma.
heat; secondary
If these low-density silica-rich magmas reach the surface, they tend to produce _________ that we associate with convergent plate boundaries.
explosive eruptions
transfer of energy / thermal energy
heat
exogenic
external
asteroids has its own _____
gravity
____ is important in keeping earth geologically alive
heat
atoms of the same element that have the same amount of of protons but different number of neutrons
isotopes
this results in different atomic mass
isotopes
To have significant internal heat, a planet must be large enough to have sufficient radioactive material, and large enough to provide some insulation to retain that heat. So small asteroids, for example, don’t have enough _____ to be _____ active. However, there is also an energy source that has affected all planets, regardless of their size.
internal heat; geologically
