Exam 1 Flashcards
geologic record is divided into 3 eons
The Archaean, The Proterozoic and the Phanerozoic
How long ago was earth formed
4.5 bya
Terrestrial planets (inner planets) Mercury, Venus, Earth and Mars
metallic cores (iron and nickel, surrounded by rock), High density, Little atmosphere
Jovian planets (outer planets) Jupiter, Saturn, Neptune, Uranus and Pluto)
Metallic cores (iron and nickel, surrounded by liquid helium), low density, lots of atmosphere, most have rings and numerous satellites
what information is used to calculate the age of the earth?
age of meteorites (should be the same age as planets)
why are meteorites used to calculate the age of the earth?
they are materials left over from formation of inner rocky planets when solar system formed
what chemicals are in the inner core
iron (94%) Nickel (6%)
what chemicals are in outer core
iron (85%), oxygen (5%), Sulfur (5%), Nickel (5%)
what chemicals are in the mantle
oxygen (44%), calcium (2.5%), magnesium (22.8%), silicon (21%), aluminum (2.4%), iron (6.3%)
Do s-waves pass through the core?
No, that’s how they know the core is liquid
Do p-waves pass through the core?
yes
premordial helium
there is no processes on earth capable of creating 3H. we find 3h in rocks and fluids thats how we know earth is still degassing. primordial helium emanates from the ground at sites of lava plumes like those found in hawaii
topography
defining form and shape
geomorphology
focuses on the evolution of topographic and bathymetric features
continental crust
20 to 60 km thick, made of granite, less dense, most is above sea level, light color, coarse
oceanic crust
only about 10 km thick, made of basalt, very dense, below sea level, dark color, fine texture
emergent coasts
where tectonic forces are pushing upwards (usually active continental margins). sea cliffs and marine terraces
submergent coasts
where sea level is rising faster than land and/or coastal areas are sinking
what type of coast are estuaries associated with
submergent coastlines formed when sea level rises and flood existing river valleys
continental margins
the submerged edge of continents they include: continental shelf, slope, rise and submarine canyons
they are influenced by tectonic uplift and subsidence.
they are areas of high sediment deposition from continents
what do active continental margins have
narrower shelf, deep sea trench, tend to be narrower (like west coast), may have high sediment accumulations but sediments go into deep trench
what do passive continental margins have
thick accumulations of sediments, wider shelf, a continental rise, tend to be wider (like east coast)
where are active margins location
around the pacific
where are passive margins located
around the Atlantic and parts of the Indian ocean
what is the continental shelf’s geomorphology influenced by?
erosion and deposition of sediments on beaches, at high latitudes glaciers and glacial deposits, mid-latitudes terrigenous fluxes and waves, low latitudes more carbonates
____ changes have great impacts on morphology and erosion
sea level
continental slope
slope between the outer edge of the continental shelf and deep ocean floor (from 100-200m to 1400-3200m depths)
shelf breaks
marks the boundary between the relatively flat continental shelf and the drop off into deeper water of the continental slope
continental rise
a wide gentle incline from a deep ocean plain to a continental slope
mid-ocean ridges
associated with divergence of ocean curst (new crust) and are volcanic (basalt) from consistent and frequent eruptions
crust sinks as it cools and moves away from ___
Mid-ocean ridges
new basalt forms from
diversity of lava flows and eruptions
bathymetry
measure of depth of water
the earth’s crust is ___ than the mantle, inner core, and outer core and so ‘floats’ on top of them
lighter
igneous type of rock and source material
melting of rocks in hot, deep crust and upper mantle
rock forming process of igneous
crystallization (solidification of magma or lava)
example of igneous rock
granite
sedimentary type of rock and source material
weathering and erosion of rocks exposed at surface
rock forming process of sedimentary
deposition, burial and lithification
example of sedimentary rock
sandstone
type of rock and source material of metamorphic
rocks under high temperatures and pressures in deep crust and upper mantle
rock forming process for metamorphic
recrystallization of new minerals in solid state
examples of metamorphic rocks
gneiss
intrusive
formed within the earth’s curst and thus cools slowly
extrusive
formed on the surface cool rapidly
extrusive oceanic curst
basalt (mafic)
intrusive ocean curst
gabbro (mafic)
extrusive continental curst
rhyolite (felsic)
intrusive continental crust
granite (felsic)
which is more dense oceanic curst or continental crust
oceanic crust
igneous rocks
solidification of magma, basalt and granite are two of the most common forms of igneous rock
intrusive cools ___ and ___ minerals form
slowly, more
extrusive cools ___ and ___ mineral frm
faster, less
lighter colored rocks have more ____
silica
metamorphic rock is modification of sedimentary and igneous rocks by:
heat, pressure and or chemically active solutions
ophiolites
masses of oceanic crust and underlying mantle that have thrust (or obducted) onto continental margins during subduction
the lithosphere is fairly ___
rigid
the asthenosphere is ___
plastic
isostasy
is the state of gravitational equilibrium between the lithosphere and the asthenosphere such that the crust “floats” at an elevation that depends on its thickness and density
how do we know where the plates are?
the locations of the plant boundaries and the distribution of earthquakes
what are the three types of plate boundaries?
divergent, convergent and transform boundaries
divergent boundary
two places move away from the axis of a mid-ocean ridge. New oceanic lithosphere forms
convergent boundary
two plates move toward each other, the downgoing plate sinks beneath the overriding plate
transform boundary
two plates slide past each other on a vertical fault surface
what elements are found in divergent boundaries
enriched in iron and magnesium and depleted in silica
when the plate of oceanic crust collides with plate of continental curst which plate subducts?
oceanic crust is subducted under continental plate
accretionary prism
sediment scraped off when plates subduct
how do earthquakes happen
at convergent boundaries the downgoing plate grinds along the base of the overriding plate, a process that generates large earthquake
Lithosphere
curst and upper mantle temp<1280C rigid
Asthenosphere
upper to mid mantle, temp >1280C Plastic
Lithosphere ___ while asthenosphere ___
bends, flows
ocean crust
basalt (extrusive), gabbro (intrusive),
ocean curst is more dense and mafic
continental crust
rhyolite (extrusive), granite (intrusive),
continental crust: less dense and felsic
a mineral
a solid formation that occurs naturally in the Earth
a rock
a solid combination of more than one mineral formations which is also occurring naturally
metamorphic rocks
are formed when igneous or sedimentary rocks are exposed to conditions of high heat and pressure. Examples of metamorphic rock include marble, slate, schist, and gneiss
igneous rock
is formed by the cooling and crystallization of molten magma at volcanoes and mid-ocean ridges, where new crust is generated. Examples of igneous rock are basalt, granite, and andesite
sedimentary rocks
Over time, igneous rocks may experience weathering and erosion from exposure to water and the atmosphere to produce sediments. The deposition and hardening of these sediments forms
differences between oceanic and continental curst
continental crust: thick and old >2 billion years
oceanic crust: thin and young <200 million yr
tectonic theory
earth’s lithosphere is broke into plates that move and interact. Plates move in response to forces in the mantle. plate boundaries are locations of great geologic change
paleomagnetism
a record of Earth’s magnetic field in the past
curie temperature
The Chinese figured out thousands of years ago that if you heated iron above a certain temperature (Curie temperature) and cooled it slowly you could form a magnet out of it.
Above the Curie temperature, the iron is so hot that the atoms become disordered and vibrate about.
Once the iron begins to cool, the atoms vibrate less and less and they lock into place in accordance with the field of the Earth.
After the iron is cooled all the way, the orientation in which it cooled is “locked in.”
the North Pole of the Earth has a ___ polarity
south
what causes a planet’s magnetic field?
the iron core of the Earth is an electromagnet. Core is surrounded by liquid iron and nickel, as electrons flow around the core the magnetic field is produced
characteristics of Earth’s magnetic field
nearly dipolar, approximately aligned with Earth’s rotation axis, changes slowly with time, spontaneously reverses every ~200,000 years, is at least 3 Ga old
magnetic declination
the angle between magnetic North and geographic North. The declination is positive when the magnetic north is east of true north, and negative when west of true north
normal polarity
magnetic polarity, same as today
reversed polarity
polarity chrons; the time interval of a reversal
forces that drive plate tectonics: mantle convection currents
warm mantle currents drive and carry plates of lithosphere along a like a conveyor belt
forces that drive plate tectonics: ridge push
buoyant upwelling mantle at mid-ocean ridges
forces that drive plate tectonics: slab pull
older, colder plates sink at subduction zones, because as they cool, they become more dense than the underlying mantle
Is this the way plates move about, passively dragged to and fro on
the backs of convection currents rising up from the mantle?
The answer appears to be no.
Almost all scientists now accept that the lithospheric plates somehow participate in the flow of this mantle convection, however the nature of the relationships are not well understood.
The main evidence comes from the rates of plate movement
why not along convection
the faster-moving plates (the Pacific, Nazca, Cocos, Indian, and Australian plates) are being subducted along a large fraction of their boundaries.
the slower-moving plates (the North American, South American, African, Eurasian, and Antarctic plates) do not have significant attachments of descending lithospheric slabs.
These observations suggest that the gravitational pull exerted by the cold (and thus dense) slabs of subducting lithosphere pulls the plates downward into the mantle.
the plates are not dragged along by convection currents rising from the mantle, but rather “fall back” into the mantle under their own weight.
slab pull
older, colder plates sink at subduction zones, because as they cool, they become more dense than the underlying mantle. The cooler sinking plate pulls the rest of the warmer plate along behind it.
Similar to an anchor pulling on an anchor line
slab-pull theory issues
if the only important force in plate tectonics is the gravitational pull of subducting slabs, why did Pangaea break apart and the Atlantic Ocean open up?
There are only 2 subducting slabs of lithosphere currently attached to the North and South American plates are found in the small island arcs that bound the Caribbean and Scotia seas, which are thought to be too small to drag the Atlantic apart.
Possibiilities: Overriding plates feel a force of suction from the subduction trench?
What about a pushing force?
ridge push
newly-formed plates at oceanic ridges are warm, and so have a higher elevation at the oceanic ridge than the colder, more dense plate material further away; gravity causes the higher plate at the ridge to push away the lithosphere that lies further from the ridge
What drives plate tectonics?
is not a direct result of mantle convection, but to gravity acting on density differences in the lithosphere that have resulted from its own thermal history.
Global Pattern of Volcanism:
Divergent Plate Boundaries
Basalt-producing spreading centers
mantle source for lava (decompression melting)
axial volcanoes of mid-ocean ridge
Global Pattern of Volcanism:
Volcanism in subduction zones
chains of volcanoes
island arcs
formation of new continental crust
Global Pattern of Volcanism
Intraplate volcanism
hot spots and mantle plumes
sea mounts and island chains
large igneous provinces
Why does liquid Magma form?
The Earth remains hot inside because of decay of radioactive elements.
Even though there is a lot of heat in the Earth, most of the crust and mantle remain solid because of immense pressures.
Magma forms only in special places, where conditions trigger melting of pre-existing solid rock:
decompression
addition of volatiles
heat transfer
Decompression melting
takes place where mantle rock rises slowly
as rock moves up, its pressure becomes less
temperatures remain nearly unchanged because rock is such a good insulation
Melting Due to Addition of Volatiles
when volatiles mix with hot mantle rock magma can form
volatiles are substances that evaporate relatively easily such as:
water
carbon dioxide
when volatiles mix with hot, dry rock, they cause chemical bonds to break so that the rock begins to melt
this is called flux melting
composition of lava
The composition of newly formed lava depends on several things:
The chemical species present in the melt
The temperature and pressure at which the melt cools
Whether it is intrusive or extrusive
mafic melts
Mafic melts contain a relatively high proportion of magnesium and iron oxide compared to silica,
ma in mafic stands for magnesium and -fic comes from the Latin word for iron
felsic melts
have a fairly high proportion of silica compared to magnesium and iron oxide
Lava Types Basaltic Lavas aa
lava that looks like clumps of moist, freshly plowed earth.
forms when lava loses its gases and consequently flows more slowly than pahoehoe, allowing a thick skin to form.
As the flow continues to move, the thick skin breaks into rough, jagged blocks.
Lava Types Basaltic Lavas pahoehoe
Hawaiian for “ropy”
Forms when a highly fluid lava spreads in sheets and a thin,
glassy, elastic skin congeals on its surface as it cools
Lava Types Basaltic Lavas pillow lavas
piles of ellipsoidal, pillowlike blocks of basalt about a meter wide
Pillow lavas are an important indicator that a region on dry land was once under water.
andesitic lavas
<1000 C
Andesite is an extrusive igneous rock with an intermediate silica content. Andesitic magmas are produced mainly in the volcanic mountain belts above subduction zones.
Viscous
The temperatures of andesitic lavas are lower than those of basalts, and because their silica content is higher, they flow more slowly and lump up in sticky masses
rhyolitic lavas
<600,800C
Rhyolite is an extrusive igneous rock of felsic composition (high in sodium and potassium with a silica content greater than 68 percent.
Highly viscous.
Rhyolitic magmas are produced in zones where heat from the mantle has melted large volumes of continental crust.
Found in Yellowstone.
mafic lava
relatively low viscosity. it can erupt in fountains, move long distances and form thin lava flows
felsic lava
when it erupts it may form a mound-like lava dome around the volcano’s vent
Major volcanic gasses:
CO2, H2O, SO2
most earthquakes occur at ______
plate boundaries (convergent, divergent and transform)
the elastic rebound theory
Explains how earthquakes recur on active faults in Earth’s crust
Plates get locked together by friction, causing a buildup of stress
Instead of slipping along the fault as stress builds up, the blocks are strained elastically near the fault.
At some point, the strength of the rocks is exceeded. Somewhere along the fault surface, the frictional bond that locks the fault can no longer hold, and it breaks.
seismic wave types
p waves - primary or compressional
s waves - secondary or shear waves
how do we study earthquakes
- we need p and s wave arrival times from at least three seismographs
- then graph of distance traveled versus time elapsed
- finally triangulate the position of the epicenter
main types of fault movement
normal fault (tension forces), reverse fault (compression forces), strike slip fault (shearing forces)
Tube Worm: Riftia pachyptila
Unusual animal
No mouth
No anus
No digestive tract
Dependent upon bacteria living in its gut or “troposome”
Gills extracts hydrogen sulfide, carbon dioxide & oxygen from seawater; blood delivers these to troposome
In return, bacteria provide nourishment for Riftia
vent ecosystems depend on 2 types of bacteria
free living bacteria, symbiotic bacteria
3 endmember types of HTVs
Type 1: the most commonly reported (Black Smokers)
mafic-hosted
high-temperature system neovolcanic end-member fluid temperatures up to 407 °C low dissolved CH4 (e.g., East Pacific Rise, 9–10 °N)
Type 2: a distinct form of high-temperature venting (also often Black smokers) associated with serpentinization of ultramafic rocks
high H2, CH4, and Fe concentrations
e.g., Rainbow, 36 °N MAR
Type 3: White Smokers
involves serpentinization of ultramafic rock but yielding substantially lower fluid temperatures exiting the sea floor (∼40–90°C).
Lost City site, 30 °N MAR
black smokers
sulfide rich, the chimney is made of sulfide ore deposits
common characteristics of black smoker fluids
Anoxic Highly reduced Acidic (pH 2-4) Enriched in Silica, Hydrogen, Sulfide, Methane, Dihydrogen, Iron, Zinc, Copper. Depleted in Magnesium
white smokers
Cooler than black smokers (300 C down to 40 C)
Further off axis that black smokers
Example Lost City
60 meter tall chimneys
Chimneys made of Carbonate
Interaction of downward seeping seawater with mafic or ultramafic rocks produces an alkaline fluid that precipitates silica and Ba or Ca sulfates when it mixes with seawater, hence the white color
High concentrations of methane (CH4) and Hydrogen (H2)
High pH (9-11)
Low concentration of magnesium
Ultra Mafic rocks
More long lived that Black Smokers
serpentinization
is a processes whereby rock (usually ultramafic) is changed, with the addition of water into the crystal structure of the minerals found within the rock
lost city
The heat that creates the venting is not a result of interaction of seawater with hot magma
The heat is a result of an exothermic serpentinization reaction
These reactions give H2 and CH4 off as biproducts
stromatolites
fossilized microbial formations (cyanobacteria) that date back 3.5 billion years
provide records of ancient life on earth
chemotroph
do not gain energy from carbon, gain energy from oxidation of electron donors
autotrophs
can fix carbon from carbon dioxide
need light and carbon to survive (in no light use energy from inorganic oxidation)
island chains
made from hot spots
island archs
made from subduction zone (aleutian islands)
Geobiology
the study of the interactions between the biosphere and Earth’s physical environment
we study this bc microbes that move chemicals around resorvoirs can tell us a lot about early Earth
how to megafauna survive at vents
H2, Ch4, H2S seeps out of rocks and provides energy for microbial species
