MEA 101 - Exam #2

name two minerals that have a sheet structure

Biotite and muscovite

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 are the processes of metamorphism

transformation of rocks by heat and pressure

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