Earth's Internal Structure

convection currents

-in 1960, proposed as driving force to move continents

axis

angle at which something is plunging downwards (syncline, anticline)

dip

angle that the plane makes with that horizontal plate

thrust fault

at convergent plate boundaries ancient rock can be thrust over younger rocks -old stuff gets pushed onto new stuff -reverse fault with a much wider obtuse angle

what lies beneath the plates

below is the asthenosphere

plate movement

-"plates" of lithosphere are moved around by underlying hot mantle convection cells -three types of plate boundaries: divergent, convergent, transform

continental drift problems

-Alfred Wegener --presented research to professionals --did not provide a plausible mechanics to explain how continents drifted

unconformities

-Grand Canyon -characteristic feature: distinct change in rock type, age, orientation, or structure

theory of pt

-John Tuzo Wilson-combined ideas of continental drift and seafloor spreading into "plate tectonics"

San Andreas Fault

-Pacific Plate (west side, moves north), North American Plate (east side, moves south) -transform boundary -right lateral -has many fracture zones -has places of divergence--> fracture zones

earthquakes and faults

-an earthquake is caused by a sudden release of energy stored in rocks along a fault -fault is a crack in a mass of rock along which there has been movement of rock layers on either side of the crack -focus- where the earthquake starts below surface -epicenter- location directly above focus on land or water -San Andreas Fault- Pacific Plate (west side, moves north), North American Plate (east side, moves south)

earthquakes

-as with volcanoes, earthquakes are not randomly distributed over the globe -at the boundaries between plates, friction causes them to stick together -when built up energy causes them to break, earthquakes occur

earthquake shadow zones

-at an angle of 103 degrees-ish (distance 11,000 kms) from the epicenter P and S waves disappear -P waves can be detected at 142 degrees (16,000 kms) --no s waves will appear again -this band of 39 degrees in which no waves are observed is called the Earthquakes shadow zone -p waves disappear 105-140 and s waves disappear at 105 -analysis of seismic waves have resulted in the inference of Earth's interior --s waves cannot pass through the liquid outer core

Igneous rocks

-begins as magma -can form: --when rock is heated --pressure is released --when rock changes composition -magma freezes between 70-1250 degrees C -magma is a mixture of many minerals

continent-oceanic crust collision

-called subduction -subduction- oceanic lithosphere subducts underneath the continental lithosphere --oceanic lithosphere heats and dehydrates as it subsides --the melting rising forming volcanism --ex: Andes

biostratigraphy

-certain fossils were only alive at particular periods of time --knowing their range of existence helps you date the sedimentary layer -relative ages determined from fossil assemblages -biotic changes are a function of extinctions and evolutionary processes -datums (reference points through which measurements are made in geology) record timing of biotic changes --first appearance and last appearances --age-dependent characteristics --boundaries calibrated by absolute ages -temporal records of life: --recognition of species unique to a particular time interval --index fossils

earth's dynamic surface

-characterized by continuous change -earthquakes seem to happen in specific locations

stratigraphic correlation

-columns --sequential order of deposition determined by correlation of separate, related stratigraphic records --unconformities may be recognized but uncertainties may persist

relative age dating

-comparative records of time --nature rock records --principles of stratigraphy ---deposition, succession, continuity, and correlation

lithosphere

-consists of continental, oceanic and upper part of mantle -continents composed of granite-type rock, quartz, and feldspar minerals, density +2.8 g/cm^3 -oceanic crust formed of basalt; basalt rich in iron/magnesium minerals, density +3 -rigid layer of crust and mantle overlying partially-molten astheosphere

seafloor spreading

-continental drift reexamined in 1960s with new information -new theory developed- seafloor spreading -supporting evidence for seafloor spreading: --world seismicity --volcanism --age of seafloor --palomagnetism --heat flow -theory combining continental drift and seafloor spreading termed "plate tectonics" -new seafloor created at the mid-ocean ridge and destroyed in deep ocean trenches

Sequence of stratigraphy: principles

-controls on the sedimentation process: --sediment production and accumulation caused by: ---sea level and water depth, accommodation space ---tectonic subsidence-accommodation space ----climate- weathering rates, grain production --cycles in these variables operate over different time scales --result from multiple studies of these cycles ---a temporal record of changes in sea level -spatial arrangement of stratigraphic units --lateral and vertical relationships in para sequences --predictable, recognizable sequences develop -depositional sequence --sequential order of characteristic elements ---sequence boundaries, etc. --relevance: defines a sea-level change

core

-dense -iron and nickel -inner core-->solid-->a lot of pressure -outer core-->liquid

evidence of internal structure

-density --calculate density of earth --speculate on probable compositions -meteorites --use composition and age to determine composition and age of earth -seismic waves --travel times and direction give indication of internal structures of earth

geologic structures

-different stresses result in various forms of strain (geologic structures) --folds (compressive strains may cause ductile strain) --faults (any type of stress may cause brittle strain. The type of fault depends on the type of stress)

stresses of plate boundaries

-divergent (tensional)--> move apart -convergent (compressional)--> move together -transform (shear)--> slide past each other

cross cutting relationships

-event sequence --younger units cross-cut older units

Iceland

-example of continental riftland -has a divergent plate boundary running through its middle

volcanoes

-form from subduction, rifting, and hotspots -hotspot volcanoes: hot mantle plunges breaking the surface in the middle of a tectonic plate--> can form an island ex: Hawaii -the tectonic plate moves over a fixed hotspot forming a chain of volcanoes --the volcanoes are younger from one end to the other

Sedimentary rocks

-formed by erosion -sediments are moved from one place to another -sediments are deposited in layers, older on bottom -layers become compacted and cemented together -formed at or near the earths surface -no hear or pressure involved

evidence supporting continental drift

-geographic fit of continents-->continents seem to fit together like pieces of a puzzle -fossils-->similar distribution of fossils ex: Mesosaurus -mountains-->mountain ranges match across oceans -glaciation-->glacial ages and climate evidence

how do we know what the earth is made of

-geophysical surveys: seismic, gravity, magnetic, electrical, geodisy --acquisition: land, air, sea, and satellite --geological surveys: field work, boreholes, mines

Constant metamorphism

-heated by nearby magma--> only heat no pressure -pool of mama and new rock -increased temperature changes the composition of the rock minerals and changed into new materials -hornfels- fine grained, non foliated

mantle

-less dense than the core -mostly solid -upper mantle is partially molten -iron and magnesium silicates

Metamorphic rock

-meaning to change shape -changes with temperature and pressure, but remains solid -usually takes place deep in the earth

origin of the earth

-meteors and asteroids bombarded the earth --increased the mass --therefore increased gravity -gravitational compression --gravitational energy turned into heat --radioactive elements are unstable --over time became more stable, released heat -density stratified planet

Chemical sedimentation

-minerals crystallize out of solution to become rock -limestone- forms from the accumulation of shell, coral, algae, and fecal debris --most commonly forms in clear, warm, shallow marine waters

plate tectonics

-most of the continents fit together like a puzzle -the Earth's crust is divided into 12 major plates which are moved in various directions -this plate rotation causes them to collide, pull apart, or scrape past each other -each type of interaction causes a characteristic set of Earth structures or "tectonic features" -the word, tectonic, refers to the deformation of the crust as a consequence of plate interaction

fault

-movement occurring along a discontinuity -brittle strain and subsequent movement as a result of stress -fault type depends on the type of stress

Rocks

-naturally occurring solid mixture of one or more minerals, or organic matter -classified by how they are formed, their composition, and texture -change over time through the rock cycle

law of initial horizontality

-orientation of beds when deposited -constraints on original orientation --sediments are deposited as horizontal beds --principle only applies to sedimentary rock formed in an aqueous environment -evidence of deformation --non-horizontal sedimentary rocks --modified by post-depositional events (folding, fractures, faulting)

crust

-outermost layers -continental- granite--> density=2.8g/cm^3 -oceanic-basalt-->density=3g/cm^3 -very thin and rigid

principles of pt

-plate boundaries have high degree of plate activity--> mountains, earthquakes, volcanoes

what tectonic plates are made of

-plates are made up of a rigid lithosphere -lithosphere is made up of the crust and the upper part of the mantle

P waves

-primary waves or compression waves vibrate parallel to the direction of movement--> longitudinal -travel faster than any other waves (6-8 km/s) -travel through solids, liquids, and gases

sequence stratography

-progression of sedimentary rocks from the change in sea level --certain areas were covered in water and the sea will deposit sediment differently than the way sediment is deposited above sea level

law of superposition

-relative ages from sequence of rock deposition -will show you the order of layered units --a rock unit is younger than the one below and older than the one below -stratigraphic column: --temporal succession of rock units --deposition is not necessarily continuous, but is sequential

Organic sedimentation

-remains of plants and animals -coal- forms from the accumulation and preservation of plant material

continental drift evidence

-researches noted geographic fit of continents --atlantic formed by separation of africa from s. america -Seuss, 1885, proposed super continent by studying fossils, rocks, mountains -Wegener and Taylor, early 1900s, proposed continental drift and Pangaea

tectonic stresses

-resulting from internal energy (heat driving convection) strains (deforms) the mantle and crust -bend rocks i.e. ductile strain (folds) -breaks rock i.e. brittle strain (joints) -moves large blocks along faults and releases energy--> earthquakes

salt domes

-rising of less dense salt -stretches overlying crust -forming faults and oil traps

S waves

-secondary waves or shear waves vibrate back and forth perpendicular to the direction the waves is moving--> transverse -slower than p waves (4-5 km/s) -travel through solids only

deposital succession

-sedimentary rock is constantly deposited as beds in rock units -this allows a record to be preserved of how sediment was deposited -beds are often discontinuous -beds can be eroded or lost --results in a gap in the temporal head ---known as "unconformity" or "hiatus"

law of lateral continuity

-spatial relationships --sediments form as continuous layers --individual horizons or layers thin or end only when the environment of deposition changes --enables correlation of beds with specific characteristics

divergent boundaries

-spreading ridges apart -as plates move apart new material is erupted to fill the gap

Chemostratography (or isotope stratigraphy)

-stratigraphic variations in specific chemical or isotopic characteristics --choose stable isotopes --isotopes --molecules --organic matter

chemostratigraphy

-study the chemical composition of the rock -those changes can be identified with particular time periods

magnetostratography

-studying magnetic reversals --polarity will reverse about every 200,000 years --knowing if a piece of rock layer has a normal or reverse polarity will help date the layer -approach based on intermittent, irregular reversal of Earth's magnetic field -rocks record field at time of formation (cooling)--> based on iron -magnetic signals preserved in stratigraphic sections show alternating sequence of polarity -series of polarity shifts --normal (modern) --reversal (opposite) -polarity intervals are independent of lithography --vary in duration -sequence of polarity reversals recognized --major interval --minor interval ---require excellent stratographic resolution --globally uniform series of time dependent reversals --ages determined by absolute dating -record compiled from multiple overlapping sequences -correlations to stages often based on biostratigraphy --palynology- plant remains

L waves

-surface or long waves- vibrations travel along Earth's surface in a circular motion at relatively slow periods (2 km/s) like waves in a pond -do more damage because they produce more ground movement

locating the epicenter of an earthquake

-the difference in travel time between p and s waves can be used to determine the distance from a station to the epicenter -the farther a station is from the epicenter, the greater the time interval from the arrival of p and s waves -to determine the exact location of an epicenter, its distance from 3 stations must be determined and 3 circles drawn -as distance from the epicenter increases, the greater the interval between p and s waves

structure of the earth

-the earth is made up of 3 main layers: core, mantle, crust -the crust: it's where we live --the earth's crust is made of: continental and oceanic crust --continental: thick (10-70 km), buoyant (less dense than ocean), mostly old --oceanic: thin (less than 7 km), dense (sinks under continental crust), young

convergent boundaries

-three styles of convergent boundaries -continent-continent collision -continent-oceanic crust collision -ocean-ocean collision

velocity of seismic waves

-velocity depends on the material they are passing through --increase density and pressure- greater the velocity --waves are retracted or bent as waves pass through material with different densities

Pacific Ring of Fire

-volcanism is mostly focused at plate margins

seismic waves

-when earthquakes occur, waves of energy and seismic waves travel outward from the earthquake focus -2 types of waves are produced at the same time but each behaves differently within the earth

ocean-ocean collision

-when two oceanic plates collide and one moves over the other which causes it to sink into the mantle forming a subduction zone --the subducting plate is bent downward to form a very deep depression in the oceanic floor known as a trench

Brecchia

Composed of large fragments filled with a matrix of smaller particles or a mineral cement that binds the rock together

Fine-grained

Cools quickly with little to no crystals

Mafic

Dark colored rocks that are rich in calcium, iron, and magnesium, poor in silicon

Obsidian

Dark colored volcanic glass that forms from the very rapid cooling of molten rock material, cools, crystals don't form

Extrusive

Forms when magma erupts into the earths surface (lava), cools quickly with very small or no crystals formed-->fine

Strata

Layers of rock

Felsic

Light colored rocks that are rich in elements such as aluminum, potassium, silicon, and sodium

Clastic

Made of fragment of rock cemented together with calcite or Quartz

Intrusive

Magma pushed into surrounding rocks below the earths surface-->coarse

Coarse-grained

Takes longer to cool, giving mineral crystals more time to grow

Stratification

The process in which sedimentary rocks are arranged in layers

tools for relative age dating

biostratigraphy, magnetostratography, sequence stratigraphy, chemostratography

reverse fault

compressive stress causes the hanging wall to move upward relative to the foot wall

earth's interior

core mantle

tectonic plates

earthquakes happen at tectonic plate boundaries

syncline

fold like a bowl caused by pushing together

anticline

fold like an arch cause by pulling apart

continent-continent collision

forms mountains ex: Alps, Himalayas

strike

line of intersection between the plane and the horizontal surface

outer core

liquid iron, convecting (magnetic field)

seismograph

measures the intensity of earthquakes

buckling

old in the middle

horst

older rocks are exposed along the ridges formed by the horst

evidence for seafloor spreading

paleomagnetism- earth has a magnetic field- possibly caused by rotation of solid inner core in liquid outer core (both mostly iron) -when rocks cool at the Earth's surface, they record earth's magnetic field (normal or reverse polarity) -studies indicate alternating stripes of normal and reverse polarity at the mid-ocean ridge

crust (lithosphere)

rigid, thick 5-30 km

inner core

solid iron

mantle (asthenosphere)

solid non-magnesium silicate, plastic, convecting

defining fault orientation

strike of fault plane parallels the fault trace and fault scrape -direction of dip of the fault plane indicates the hanging wall block

laws governing stratigraphic relations

superposition, initial horizontality, lateral continuity, cross-cutting relationships

brittle strain

when shallow crust if strained and rocks tend to exhibit brittle strain -tensional strain causes brittle strain and formation of sets of normal faults

transform boundaries

where plates slide past each other ex: San Andreas fault

bending

young in the middle

graben

younger rocks lie beneath the grabens