GEO WORD DEFINITIONS EXAM 2

Angular Conformity

A boundary where older tilted layers are covered by younger flat layers
💡 Rocks were bent, eroded, then new layers formed

Cross-cutting relationships

A feature that cuts another rock is younger than it
💡 The “cutter” happened last

Disconformity

• Missing time between parallel sediment layers
  💡 Looks normal but time is missing

Nonconformity

• Sedimentary rock on top of igneous or metamorphic rock
  💡 Big gap in Earth history

Unconformity

A surface showing missing time (erosion or no deposition)

Superposition

• Bottom layers are older, top layers are younger

Angle of dip

The steepness of a tilted rock layer

Strike

The direction of a rock layer on a map

Fold

Rock layers that bend (don’t break)

Anticline

• Fold shaped like an arch

• Oldest rocks in center

Syncline

• Fold shaped like a bowl

• Youngest rocks in center

Fault

A break where rocks move

Hanging wall

The top block of a fault

Footwall

The bottom block of a fault

Dip-slip fault

Movement is vertical

Normal fault

• Hanging wall moves down

• Caused by tension

Reverse fault

• Hanging wall moves up

• Caused by compression

Strike-slip fault

Movement is sideways (horizontal)

Left-lateral / Right-lateral fault

Direction the other side moves
💡 Like cars passing each other

Oblique-slip fault

Movement is both vertical + horizontal

Compressive stress

Rocks are pushed together

Tensional stress

Rocks are pulled apart

Shear stress

Rocks slide past each other

Brittle behavior

Rock breaks

Ductile behavior

Rock bends/flows

Uniformity (uniformitarianism)

Same processes today happened in the past

Absolute (numerical) age

Actual age in years

Isotope

Atom with different number of neutrons

Parent isotope

Original unstable atom

Daughter product

New stable atom after decay

Radioactive decay

Parent → daughter over time

Half-life

Time for half of parent atoms to decay

Elastic rebound theory

Rocks bend → snap → release energy

Focus

Where earthquake starts underground

Epicenter

Point directly above focus on surface

Magnitude

Amount of energy released

Moment magnitude

Modern scale for earthquake strength

Intensity

How strong shaking feels

Modified Mercalli scale

Measures damage/feeling

Amplitude

Height of seismic wave

Body waves

Travel through Earth

P-wave

Fastest wave

Surface wave

Causes most damage

Aftershock

Smaller quake after main one

Tsunami

Giant ocean wave from earthquake

Plate

Piece of Earth’s lithosphere

Plate tectonics

• Theory that plates move and interact

Asthenosphere

Soft layer plates move on

Convection

Hot rises, cold sinks

Mantle plume

Rising hot material → volcanoes

Divergent plate boundary

Plates move apart

Convergent plate boundary

Plates collide

Transform plate boundary

Plates slide past

Subduction

One plate sinks under another

Seafloor spreading

• New crust forms at ridges

Pangea

Supercontinent of all continents

Continental drift

• Continents move over time

Craton

• Stable old part of continent

Terrane

Broken piece of crust added to a continent

Orogeny

Mountain-building event