MEA 101 - Exam #2
name two minerals that have a sheet structure
Biotite and muscovite
what are the processes of metamorphism
transformation of rocks by heat and pressure
how old do scientists believe the earth is
4.5 billion
how landscapes/erosion are dated
lands start being flat. cosmic ray exposure ages. older than the rocks that are deposited onto it.
what are graded beds
largest grains are on the bottom and the finest are on top
uplift
mountains and isostasy as volcanoes erode isostasy causes to lower portion to rift expose deeper parts of mountain
when mantle melts, does it melt completely?
no
mineral calcite
non-silicate. calcium carbonate. limestone. marble. soft. used for sculptures.
mineral gypsum
non-silicate. wallboard.
what is a fossil
preserved remains of plants and animals, original material usually totally replaced by new materials, in rare cases original material preserved for 60+ millions of years
age and organisms of paleozoic
(ancient life) dominated by marine life, land plants, reptiles, insects, amphibians 540 -250 million
age and organisms of mesozoic
(middle life) the age of dinosaurs 250 - 65 million
age and organisms of cenozoic
(recent life) the age of mammals 65 million - now
age and organisms of precambrian
(simple life) dominated by bacteria and algae. 4500 - 540 million most of earths history few fossils, none that can be used for relative dating
after two half lives, the ratio of parent to daughter isotope is 1:__
3
structure of quartz
3D framework
structure of feldspar
3D lattices
how many bonds does silicon make in minerals
4
age of oldest known rocks
4 billion
how old are the oldest rocks
4 billion
age of the earth
4.5 billion
what effect does liquid in a magma have on melting temperature
Adding water lowers melting point
name two mineral types that have chain structure
Amphibilole and pyroxene
how does transport affect clast shape
Become more rounded
structure of amphibole
Chain
structure of pyroxene
Chain
what element is most responsible for minerals being dark
Iron
what effect does pressure have on melting temperature
Melting temperature decreases with pressure
8 common elements in rocks
O, Si, Al, Fe, Ca, K, Na, Mg
ages of 4 major time intervals
Precambrian: 4.5 billion - 540 million Paleozoic: 540 - 250 million Mesozoic: 250-65 million Cenozoic: everything since dinosaurs
beginning and end of each era
Precambrian: earth was formed and cyanobacteria provided oxygen. Paleozoic: life became more diverse, hard shelled, land plants and reptiles developed. Ends with the biggest extinction. Mesozoic: ended with extinction event
what causes melting in the upwelling mantle beneath a spreading center
Pressure released melting
structure of biotite
Sheet
structure of muscovite
Sheet
what is the difference between mafic, felsic, and intermediate rocks
Their concentrations of iron and silica. mafic- low silica felsic- high silica
what common elements are radioactive
U, K, Rb
what is the most important factor controlling the grain size of igneous rocks
Where/how quickly they cooled
where are granites found in relation to volcanoes
above volcanic hotspot
the difference between relative and absolute ages
absolute age is actually how old the rock is while relative dating is just concerned with which rocks are older in the same location
which of the following is not a factor that controls weathering rates of rocks
all of the above control rock weathering rates
which type of rock may undergo weathering at the earth's surface to form sediment
all of them
intermediate fine grained
andesite
mafic fine grained
basalt
value of fossils in dating rocks
because fossils and the rocks there are in have the same age, fossils can be used to give the age of the rock. Provides age when compared with sequence that has been dated by radiometric dating.
gabbro can be found
below the ocean floor
when did complex life with hard shells develop
cambrian
what are the three types of sedimentary rock with representative examples?
clastic - sandstone chemical - halite biochemical - coal
what are the steps of the rock cycle
compaction & cementation This happens when sediments become a solid rock. (example: sand becomes sandstone) heat and pressure These are two geological forces that change other rock types into metamorphic rock. weathering, erosion & deposition This happens when rocks are worn down, broken apart or when parts of rocks are relocated in a pile of sediments.
how are sedimentary units dated
comparatively
what is the difference between confining pressure and differential stress
confining pressure is when pressure is felt the same from all directions while differential stress is when another force such as tectonics affects the rocks and the combined stress is greater in some directions than others
clastic rock
consisting of pieces derived from other rocks. form on the earth's surface in low-temperature environments such as sand dunes, rivers and beaches. they also make up some volcanic rocks.
what is contact metamorphism, where does it occur
contact metamorphism is characterized by high temperature and low pressure conditions when the crust is heated near magma rising from an underlying subduction zone
where does major metamorphism occur (tectonically)
convergent boundary
three ways to study earthquake hazard
cross cutting relations to determine which units are cut by the fault fault scarps which tend to be steep and uneroded when first formed soils and rock samples to predate and postdate fossils
how did oxygen become abundant in the atmosphere
cyanobacteria produced oxygen through photosynthesis
three ways to predict volcanic hazard
dating the relative ages of the rocks estimate the ages of lavas and volcanic cones based on erosion isotopic method
adding water acts as a catalyst to ____ the melting temperature of rocks
decrease
intermediate coarse grained
diorite
what does a radioactive decay curve look like
downward slope
nonconformity
erosion surfaces form on top of rocks that are not layered. A large nonlayered rock is uplifted to the surface and then buried by sand and cobbles
why does geology often vary horizontally when units of the same age are exposed
erosion, change in thickness, restricted event...
deposition
eventually sediment carried by streams or river will be deposited deposited when current slows maybe in lake eventually to ocean during floods may outside river banks
how to determine relative ages from crosscutting relationships
faulting is younger than the rock that it cuts through
which composition of igneous rock has the lowest melting point
felsic
igneous rock
form from solidification of melt (magma). crystalline rock. extrusive-erupt on surface intrusive-crystallizes beneath surface
value of fossils in correlating rocks
fossils allow correlation between locations. many sedimentary rocks have enough fossils to establish what type of organisms lived at the time the rock was deposited.
how are fossils used to correlate rocks
fossils establish how old the rocks are, and rocks with the same fossils are the same age. fossils that lived for a short time, index fossils, are much more useful.
mafic coarse grained
gabbro
what causes vesicles in igneous rocks
gas expansion during eruption
what is a turbidite
geologic deposit of a turbidity current, which is a type of sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean
how do graded beds form
graded beds are formed as a strong current beings to lose velocity and drops progressively finer sediments so the largest grains are on the bottom and the finest are on top
solidification
grain size reflects cooling rate
felsic coarse grained
granite
where is most magma emplaced
greater volume emplaced at depth
definition of a mineral
has a regular internal (atomic) structure. has a specific composition (within specified limits)
how does water get into a subduction zone
hot water circulates in ridge, added in pores and in minerals
metamorphism and deformation
increased pressure from overlying rock and burial or tectonic processes can change rock metamorphism risks recrystallize to form new minerals - generally harder heated rocks can bend - tectonic forces often deform rocks
what are the processes that convert sediment to rock
lithification turns sediment into rock and it consists of compaction and cementation
what is the difference rock behavior between low pressure and temperature and high temperature and pressure
low pressure and higher temperature contribute to melting. low temperature and higher pressure will be solid.
what type of rocks are found in a spreading center?
mafic
what does limestone become when it is metamorphosed
marble
what caused the dinosaurs to go extinct
meteor
if granite was transported from the mountains to the ocean, what mineral would most likely remain at the end of the journey
quartz
how are fossils preserved
quick burial in mud and no oxygen. the mud turns to shale by lithification
three ways to study flood potential/history
records of stream flow determine when the floodplain and terraces were last flooded by oils development carbon 14 dating
felsic fine grained
rhyolite
which of the following rocks are volcanic and have a high silica content
rhyolite
weathering
rock at or near surface water dissolves some components freezing/thawing open cracks, breaks rocks apart roots help pry open cracks weathering breaks rocks into smaller pieces and chemically weakens rocks and minerals
crystalline rock
rocks made of crystals. contain interlocking crystals that grew together. typically formed in high-temperature environments from crystallization of magma, metamorphism, or from precipitation of hot water
the principle of original horizontality
sedimentary rocks are originally deposited in horizontal layers, if you find folded or tilted layers the deformation came after the deposition
what kind of rocks are most likely to have fossils and why
sedimentary rocks because they have layers, and fossils wouldn't form in the crystallization of magma (igneous) or heat and pressure (metamorphic)
what do mudcracks mean
sedimentary rocks that have mudcracks must have been deposited on land and in environments where wet sediment could periodically dry
where are sediments deposited and why are they deposited there
sediments are deposited when the current slows. may be in lake, riverbanks, and eventually to the ocean
burial and lithification
sediments buried as other sediments deposited on them can bee buried deeply burial increased pressure compacts sediment fluids can cement lithification is process of turning sediment into rock, compacted and cemented
structure of clay minerals
sheet
what is the order of metamorphic grade for gneiss, schist and slate
slate is lowest schist gneiss is highest grade
what are ophiolites
slices of oceanic crust that have been thrust onto the edge of continental plates
what does a porphyritic texture tells about the rock history
some crystals formed in magma chambers at a greater depth and then the magma rose and solidified at the surface into the remaining fine-grained matrix around the larger crystals.
what is sorting and how does it happen
sorting describes the size range of clasts in sediment and it happens through transportation by wind or water
melting
takes place deep in earth, seen as volcanism
what is the basic structure of a silicate mineral
tetrahedron
why are sediments usually deposited in flat beds
the current slows in flat beds which causes most of its sediment to spread out and be deposited
the principle of uniformitarianism
the same processes we see today operated in the past
how does melting occur above a subduction zone
the subducted slab melts, and the magma trapped under the continental plate heats the surrounding rocks which causes partial melting
what is a half life
the time required for any specific property to decrease by half
which example best explains what a rock endures during physical weathering in a cold, snowy environment
the water freezes and thaws, breaking up the rock and minerals
what happens to rocks as they move further from their source
they become better sorted
what is regional metamorphism, where does it occur
typical metamorphism in the upper crust by temperature and pressure
erosion and transport
water from rain and snow melt washes particles down slope to local stream glaciers scour rock and carry masses of material gravity pulls loose particles down slope
disconformity
when rock layers are not tilted before they are covered in younger layers, but the boundary represents millions of years of time
angular unconformity
when the underlying layers have been tilted
what causes cross bedding
wind or water because when sand and silt move over a dune or underwater ripple, grains accumulate in thin beds on the down-current side of the dune or ripple.
when mantle melts, does it usually melt to a melt of the same composition as the source rock?
yes
is the decay rate of radioactivity the same under all conditions
yes, radioactive decay occurs at a constant rate
what can you tell from fossils in sedimentary rocks
you can tell the age of the sedimentary rock, and certain characteristics about the time when the rock was formed
how to determine relative age of sequence of rocks
younger rocks on top, rocks are older than the intrusion, faulting is younger than the rocks that the fault cuts through, and layers are younger than the clasts it contains
