Exam 2 geo110 jmu

What are the two main types of deformation?

Folds (ductile) and Faults (brittle)

What causes rock folding?

Compressional forces that bend rocks without breaking.

What causes faulting?

Brittle deformation when rocks break under stress.

What are the three parts of a fault?

Hanging wall (headwall)

What happens in a normal fault?

Hanging wall moves down; caused by tensional (pull-apart) stress.

What happens in a reverse fault?

Hanging wall moves up; caused by compressional stress.

What are the three main fold types?

Monocline

What theory explains how earthquakes occur?

Elastic rebound theory — rocks bend

What is the focus (hypocenter)?

The point inside Earth where an earthquake starts.

What is the epicenter?

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

What is slip?

The amount of movement along a fault during an earthquake.

What are seismic waves?

Energy waves that radiate from the focus of an earthquake.

What are the two main types of body waves?

P-waves and S-waves.

What are P-waves?

Primary

What are S-waves?

Secondary

What are surface waves?

Waves that move along the surface and cause the most damage.

How do P and S waves help locate the epicenter?

Measure the S–P time difference at three stations and triangulate.

How does the S-wave shadow zone prove the core is liquid?

S-waves can’t travel through liquids

What does the P-wave shadow zone indicate?

Refraction by the liquid outer core — evidence of layering inside Earth.

Which crust is thicker and felsic?

Continental crust.

What is the Moho?

Boundary where seismic waves speed up dramatically — base of the crust.

What is the asthenosphere?

A ductile layer in the upper mantle where seismic waves slow down.

Who discovered the Earth’s inner core?

Inge Lehmann.

What does “isostasy” mean?

The balance of crust “floating” on the denser mantle.

What scale measures earthquake magnitude?

Richter Scale (logarithmic).

How much more energy is released per Richter unit?

About 30 times more energy for every whole-number increase.

How much greater is amplitude per magnitude unit?

10 times greater amplitude.

What is the main hazard that causes most deaths from earthquakes?

Tsunamis.

What generates Earth’s magnetic field?

Electric currents in the liquid outer core.

What is paleomagnetism?

Ancient magnetism preserved in rocks that records Earth’s past magnetic orientation.

What did magnetic striping on the ocean floor reveal?

Symmetrical magnetic reversals — evidence of seafloor spreading.

What’s the difference between relative and absolute dating?

Relative = sequence of events; Absolute = numerical ages using isotopes.

What are the laws of relative dating?

Original horizontality

What are the three main types of unconformities?

Angular

Describe an angular unconformity.

Tilted rocks below flat layers above.

Describe a disconformity.

Erosion surface between parallel sedimentary layers.

Describe a nonconformity.

Sedimentary rocks above eroded igneous/metamorphic rocks.

What is radioactivity?

Spontaneous transformation of one atom into another by particle emission or capture.

What is radiometric dating?

Using isotope decay rates (half-lives) to find the age of rocks.

Who proposed continental drift?

Alfred Wegener (1912).

What evidence supported continental drift?

Continental fit

What was missing from Wegener’s theory?

A mechanism to explain how continents moved.

What theory replaced continental drift?

Plate Tectonics (unified in 1972).

What drives plate movement?

Mantle convection currents

What are the three types of plate boundaries?

Divergent (pull apart)

What is seafloor spreading?

New crust forms at mid-ocean ridges and moves outward.

What confirmed seafloor spreading?

Magnetic anomalies and deep-sea drilling showing older rocks away from ridges.

What does the lithosphere include?

Crust and uppermost solid mantle.

What is the asthenosphere’s role?

It’s the soft

What does COPDMPS stand for?

Continental rifting

What is the Wilson Cycle?

The repeated opening and closing of ocean basins through plate tectonics.

What happens during continental rifting?

The crust stretches and breaks apart — new ocean may form.

What happens at a passive margin?

Sediment accumulates along stable continental edges.

What marks the destruction stage?

Subduction of oceanic crust beneath another plate.

What happens during mountain building

Continental collision forms major mountain ranges.

What happened during the Cambrian?

Explosion of marine life; formation of carbonate platforms.

What happened during the Ordovician–Silurian?

Taconic orogeny and early land plants.

What characterized the Devonian period?

“Age of Fishes”; Acadian orogeny; land colonization by plants.

What major event occurred in the Pennsylvanian?

Alleghanian orogeny formed Pangaea; widespread coal swamps.

What defined the Permian?

Pangaea fully assembled; ended with mass extinction.

What happened during the Mesozoic?

Pangaea broke apart; Atlantic Ocean opened; age of reptiles.

What characterizes the Cenozoic?

Age of mammals; ice ages; modern continents and climate.

Who discovered the inner core?

Inge Lehmann.

What is the “Moho”?

Boundary separating crust from mantle

What is isostasy?

Concept that the crust “floats” in gravitational balance on the mantle.

When was plate tectonics unified as a theory?

1972.

What is the main cause of tsunamis?

Sudden seafloor displacement from undersea earthquakes.