GEOL 104 Midterm

Catastrophism

Catastrophism

A principle that states that Earth's landscapes were shaped primarily by catastrophes

Uniformitarianism

A principle that states that Earth's landscape was formed gradually over long periods of time

How did the moon form?

A large impact around the size of Mars crashed into Earth and liquified it

Hydrosphere

The water portion of the Earth

Atmosphere

The gaseous envelope surrounding the Earth

Geosphere

The solid part of the Earth

Biosphere

Consists of all plants and animals on Earth

Continential crust

Thicker and composed of lighter material

Oceanic crust

Thinner and composed of denser material

Moho

The boundary at the base of the crust in between the crust and the mantel

What is the mantle composed of?

Solid rock made of mostly peridotite and olivine that flows very slowly

What elements is the mantle composed of?

Oxygen, silicone, and magnesium

What is the same about the inner and outer core?

Same chemical composition, different behaviour

Lithosphere

A rigid layer made up of the uppermost part of the mantle and the crust

What are tectonic plates make of?

The lithosphere

Asthenosphere

The softer layer of the mantle on which the lithosphere floats.

Lower mantle

The lowest portion of mantle where very hot rocks undergo large scale circulation

Outer core

Liquid because it is so hot and not a lot of pressure

Inner core

Solid because of the huge amounts of pressure even though it is still very hot

Seismic waves

Vibrations that travel through Earth carrying the energy released during an earthquake and can provide information about the composition of the Earth

Body wave

Seismic waves that arc through the interior of the Earth, can be primary or secondary, are faster and arrive first

Primary waves

Can travel through all of Earth's layers via compression - faster, not connected

Secondary waves

Arrives second, moves like a string - slower, connected

Glacial rebound

The process by which the surface of a continent rises back up after an overlying continental ice sheet melts away and the weight of the ice is removed

Cratons

The stable and really old inner parts of the continents

Shields

Parts of the craton where rocks are exposed and relief is low

Stable platforms

Parts of the craton covered with a thin layer of sedimentary rock

Continental margin

The boundary between continental crust and oceanic crust/the edges of continents

Continental slope

A steep incline of the ocean floor leading down from the edge of the continental shelf and transitions from continental to oceanic crust

Mid ocean ridges

Long chains of mountains on the ocean floors

What provided evidence for continental drift?

Mid ocean ridges, the fit of the continents, fossil evidence, locations of glaciations, matching climate belts and rock types

Continental drift

The hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations

Sea floor spreading

The process by which upwelling magma erupts at mid ocean ridges, cools, and then moves away collecting sediments creating new oceanic crust

Alfred Wegner

Credited for the idea of continental drift

Magnetic anomalies

Magnetic stripes in the sea floor that are symmetrical along mid ocean ridges

Earth's magnetic field

Magnetic lines of force from Earth's polar north and south, acting like a giant magnet

Paleomagnetism

The study of the alignment of magnetic minerals in rock, specifically as it relates to the reversal of Earth's magnetic poles; also the magnetic properties that rock requires during formation

Normal polarity

Dipole points to the south

Reversed polarity

Dipole points north

Magnetic reversals

When the magnetic field of the Earth reverses at irregular intervals - provides strong evidence of sea floor spreading as they are symmetric on either side of the ridge

Active margin

A continental margin that also corresponds with a plate boundary

Passive margin

Edges of continents that don't correspond with plate boundaries - wide and steep continental shelves that don't expand very far off shore

Divergent plates

Two tectonic plates that are moving away from each other

Where are divergent plates located?

At mid ocean ridges

principle of lateral continuity

sediments accumulate in continuous layers

principle of cross-cutting relations

younger features cut across older features

principle of inclusions

the rock containing the inclusion is younger than the inclusion itself

conformable

when there is no break in the rock record

unconformity

a widespread break or gap in the rock record caused by erosion and/or non-deposition of rock units resulting in no single location that has a complete record of earth's history

angular unconformity

when the orientation of layers above the unconformity is different that the layers below

disconformity

when the strata above and below the unconformity are parallel, but the contact between them represent a gap in deposition

nonconformity

separates older metamorphic or igneous rocks from younger sedimentary strata - the igneous or metamorphic rocks underwent cooling, uplift, and erosion prior to becoming the substrate, or basement, on which new sediments accumulated

william smith

noted that strata can be correlated across widely separated areas based on the fossils they contain

principle of fossil succession

fossil organisms succeed one another in a definite and determinable order - fossils have specific ranges within and across a sequence

index fossils

widespread fossil species that survived for a short time period that are used to associate strata with a specific time interval

stratigraphic formation

a set of sedimentary beds and/or volcanic layers composed of specific rocks that can be traced over a broad region

depositional contact

the boundary surface at the base of a sedimentary formation (different from faults and intrusive contacts) - can be conformable or unconformable

stratigraphic column

shows the order of units (oldest at the base), the thickness of formations, and rock types in each units

geochronology

the science of dating geologic events

C12

6 protons, 6 neutrons (stable - don't decay over time)

C13

6 protons, 7 neutrons (stable - don't decay over time)

C14 (radiocarbon dating)

6 protons, 8 (radioactive - unstable isotope) - used to date very recent geologic events - half-life only 5,730 years - produced in the upper atmosphere and absorbed by organisms - most useful tool for anthropologists, archaeologists, and historians

Potassium-Argon

K40 has a half life of 1.3 billion years - ideal for dating because potassium is found in many minerals - accurate from ~4.3 Ga to ~100 ka

Uranium - Lead dating

complex process - useful for rocks ranging from ~4.5 Ga to ~1 Ma

eon

largest subdivision of geologic time - phanerozoic is the most recent

phanerozoic eon

subdivided into the cenozoic, mesozoic, and paleozioc eras

orogens

mountain belts, linear ranges of mountains

orogeny

the process of mountain building - leads to uplift and deformation of rocks to produce geologic structures (like folds and faults)

types of deformation of rocks

displacement, rotation, and distortion

displacement

change in location

rotation

change in orientation - no change in shape

distortion

change in shape

stress

a force applied over an area (force/area) - same amount of force applied on different areas leads to different degrees of stress

strain

distortion caused by stress - the way an object responds to stress depends on the force and the area over which is applied

types of stress

compressional, tensional, shear, and confining pressure

compressional stress

object is squeezed

tensional stress

object is pulled apart

shear stress

when one object slides relative to another surface

confining pressure

object is subjected to the same stress on all sides

types of strain

contraction, stretching, and shear

contraction

caused by compression

stretching

caused by tension

shear

caused by shear stress

joint

fractures in rocks where rock bodies break but don't slide past each other - created by tensional stress - orientation can tell about the orientation of stress that caused it

veins

when groundwater or hydrothermal fluid moves through cracks and precipitates

fold

rocks bend without breaking - usually result of deformation in high-temperature and high-pressure environments

hinge line

line connecting the points of flexure or maximum curvature of the planes in a fold

axial plane

plane equally dividing the fold

limb

the planar region of a fold that lies on either side of the axial plane

brittle deformation

low temps and pressure - rocks break

ductile deformation

high temps and pressure - rocks bend

dip

angle between a horizontal plane and the plane of interest - a bed dipping at 0° is flat (not dipping) - a bed dipping at 90° is vertical - direction is described based on the direction of the steepest angle that it is dipping at

strike

the direction or trend of the intersection between the plane of interest (eg. a bed) as it intersects a horizontal plane - are always perpendicular to dips - eg. the water surface intersects the sedimentary beds along the strike line

anitcline

upfolded or arched layers - oldest layers exposed in the centre

syncline

downfolded layers - youngest layers exposed in the centre

plunging fold

axis of the fold (hinge line) plunges into the ground

domes

upward circular features - oldest rocks in the centre

basins

downwarped circular features - youngest rocks in the centre

monocline

large step-like folds in otherwise horizontal sedimentary strata - caused by differences in the hardness of the rock layers - as blocks of basement rock are displaced upward, the ductile sedimentary strata drape over them

slickensides

polished, smooth surfaces that provide evidence for the direction of movement along the fault - smooth due to friction