Geology Exam #2

What is deformation?

any change in the shape, position, or volume of rocks within the Earth’s crust due to stress

Types of Deformation

• elastic

• ductile

• brittle

What is elastic deformation?

nonpermanent, rock returns to original shape

What is ductile deformation?

• permanent, rock flows or bends

• folds occur

What is brittle deformation?

• permanent, rock breaks

• faults occur

What is a fold?

when rock layers bend or curve without breaking

• forms due to compressional forces

What is a fault?

a break or crack in the Earth’s crust where rocks have moved past each other

What are the types of folds?

• monocline

• anticlines

• synclines

• symmetrical

• asymmetrical

• overturned

• domes

• basins

What is a monocline?

a type of fold in rock layers where the layers bend in a single direction

What is an anticline?

a type of fold in rock layers where the layers are arched upward, forming a shape like an upside-down U

How do anticlines form?

form when rocks are compressed, causing them to buckle upwards during ductile deformation

Key Features of an Anticline

• rock layers bend upward

• oldest rocks are in the center of the fold

• sides of the fold dip away from the center

What is a syncline?

a type of fold in rock layers where the layers bend downward, forming a shape like a U

How do synclines form?

form when rock layers are compressed, causing them to fold downward during ductile deformation

Key Features of a Syncline

• rock layers curve downward

• youngest rocks are in the center

• sides dip toward the center

What is a symmetrical fold?

folds where everything is tilted the same way

What is an asymmetrical fold?

folds where axis aren’t parallel to each other, not tilted all the same way

What is an overturned fold?

fold where axis isn’t straight up and down, not bent one way or another

What is a dome?

when folds form in circular patterns and force pushes up at a single point

What is a basin?

when a force is pushing down at a single spot and the rocks bend at that single point

Anatomy of a Fold

• limbs

• axial plane

• plunge

What is a limb?

side of a fold, each fold has a left and right-hand limb seperate by a fold axis

What is the fold axis?

line of symmetry that’s drawn down an object

What is an axial plane?

an imaginary plane that divides a fold into two roughly symmetrical halves

What is a plunge?

the angle at which a fold’s hinge line tilts below the horizontal

• each plunging anticline & syncline have “noses” that let us know they are plunging

How do rocks break?

• joints

• faults

Anatomy of a Fault

• head wall (hanging wall)

• foot wall

• fault plane

What is a head wall/hanging-wall?

the block of rock that lies above the fault plane

What is the footwall?

the block of rock below the fault plane

What is the fault plane?

the falt or gently curve surface along which rocks break and move during a fault (slanted crack surface)

How do faults form?

when stress in the Earth’s crust becomes strong enough to break the rock and cause it to move along a fracture

What are the types of faults?

• normal (dip-slip)

• reverse (dip-slip)

• thrust

• strike-slip

What is a normal fault (dip-slip)?

• caused by tension

• hanging wall moves downward relative to footwall

• crust is being pulled apart → one side drops

What is a reverse fault?

• caused by compression

• hanging wall moves upward relative to the footwall

• crust is being pushed together → one side is pushed up

What is a thrust fault?

• type of reverse fault with a very shallow fault plane

• hanging wall moves up and over the footwall

What is a strike-slip fault?

• caused by shear stress

• rock blocks mvoe horizontally past each other

• little to no vertical movement

• left-lateral/right-lateral

What is a left-lateral strike-slip fault?

opposite side moves to the left

What is a right-lateral strike-slip fault?

opposite side moves to the left

What is an earthquake?

a shaking or vibration of the ground

Why do earthquakes happen?

• breakage of the ground along a fault

• elastic rebound theory

What is the elastic rebound theory?

explains how earthquakes occur due to the sudden release of stored energy in rocks along a fault

Anatomy of an Earthquake

• focus

• epicenter

• slip

• seismic waves

What is the focus of an earthquake?

the point inside the Earth where the earthquake actually begins

What is the epicenter of an earthquake?

the point on the Earth’s surface directly above the focus

What is the slip of an earthquake?

how much the earth moved when it broke

What are seismic waves?

• shaking we feel after the Earth broke

• measure with a seismograph

Types of Seismis Waves

• body waves

  • P-waves

  • S-waves

• surface waves

What are P-waves?

• compressional (push-pull) motion

• particles move back and forth in the same direction the wave travels

• fastest seismic waves

• can travel through solids, liquids, & gases

What are S-waves?

• shear (side-to-side or up-and-down) motion

• particles move perpendicular to the direction the wave travels

• slower than p-waves

• can travel through only solids

What are surface waves?

seismic waves that travel along the Earth’s surface during an earthquake

Do body waves travel faster or slower the deeper they go?

faster; denser material transmits energy fast and more intensely

What do we use seismic waves to study?

the interior of the earth

What do P, S, & surface waves tell us about the interior of the Earth?

• earth is layered

• the patterns of the waves through Earth’s interior

What is refraction?

the bending of a wave as it passes from one material into another where its speed changes

What is reflection?

when a wave bounces back after hitting a boundary between two materials instead of passing through

What are tsunamis?

a series of large ocean waves caused by sudden movement of the seafloor, usually due to an underwater earthquake

What is the Richter scale?

a system used to measure the magnitude (strength) of an earthquake based on the amount of energy it releases

• logarithmic scale

• measured using seismographs

• increases about 30 times for every increment

Earth’s Composition

• crust

  • oceanic

  • continental

• mantle

• core

What is Earth’s continental crust?

• thick, solid outer layer of Earth that forms the continents and landmasses we live on

• felsic

• 35 km thick

What is Earth’s oceanic crust?

• thin, denser outer layer of Earth that lies beneath the oceans and forms the ocean floor

• younger than the continental crust

• mafic

• 5-10 km thick

What is Earth’s mantle?

• thick layer of the Earth located between the crust and the core

• upper & lower mantle

• 2,900 thick

What is the Earth’s core?

• innermost layer of the Earth located beneath the mantle

• outer & inner core

• 3,500 km in radius

What is the outer core?

• liquid

• made of molten iron & nickel

• about 2,200 km thick

What is the inner core?

• solid

• made of iron & nickel

What is a Moho?

a boundary between any kind of crust in the Earth and the next thing beneath it

What is magnetic field?

• William Gilbert (1600) realized Earth is a big magnet

• refers to the invisible force field generated deep inside the planet by the movement of molten metal

• supports theory that the outer core is liquid

What is paleomagnetism?

the Earth’s magnetic field is recorded in cooling rocks that contain material that will align to a magnetic field-thermoremanent magnetism

What is the law of original horizontality?

states sedimentary rock layers are originally deposited in flat, horizontal layers

• if they are found tilted, folded, or bent, it means they were moved or disturbed after they formed

What is the law of superposition?

states in an undisturbed sequence of sedimentary rock layers, the oldest is at the bottom and the youngest layer is at the top

What is the law of cross-cutting relationships?

states any rock or feature that cuts across another rock must be younger than the rock it cuts through

What is an unconformity?

• a gap in the geological record

• things that have never been recorded

What are the types of unconformities?

• disconformity

• angular unconformity

• nonconformity

What is a disconformity?

erosion removes a part of otherwise undisturbed rock

What is an angular unconformity?

rocks below are at an angle in relation to those above

What is a nonconformity?

sedimentary rocks lie on top of igenous rocks

What is continental drift?

• proposed by Alfred Wegener in 1912

• idea that continents were once joined together in a single supercontinent and slowly moved apart

What is early evidence for continental drift?

• continental fit

• rock sequences

• glacial evidence

• fossil evidence

• polar wandering

What does continental fit mean?

the way the edges of continents appear to match together like puzzle pieces

What does rock sequences mean?

a stack or order of rock layers that formed over time in a specific region

What does glacial evidence mean?

signs in rocks and landforms that show a region was once covered by glaciars even if it is not cold there today

What does fossil evidence mean?

the discovery of identical fossils of the same ancient organisms on continents that are now far apart

What does polar wandering mean?

the apparent movement of Earth’s magnetic poles over time

What is recent evidence for continental drift?

• seafloor spreading (1960s)

• deep-sea drilling

What is seafloor spreading?

the process where new ocean crust is created at mid-ocean ridges and the ocean floor slowly moves outward

What is deep-sea drilling?

the process of boring into the ocean floor to collect samples of sediment and rock from beneath the seafloor

What is the theory of plate tectonics?

states that Earth’s outer shell is broken into large, rigid pieces called tectonic plates, & these plates slowly move over the softer layer beneath them

What is the difference between continental drift & plate tectonics?

Continental Drift:

• only continents move

• doesn’t explain how they moved

Plate Tectonics:

• entire plates move

• explains how and why the movement happened

What is the modern plate tectonics theory? (1972)

the lithosphere is divided into plates bounded by oceanic ridges, trenches, mountain rangers, and transform faults

What is radioactivity?

spontaneous transformation of one atom to another by capture or ejection of subatomic particles

What is relative geologic time?

a way of determining the order of events in Earth’s history without knowing their exact agers in years

• law of superposition

• law of original horizontality

• law of cross cutting relationships

What is absolute geologic time?

the measurement of Earth’s history using actual numerical ages rather than just ordering events

• found using radiometric dating