ENVR 202 terms

crust

where life exists, v. thin layer (100km max)

plate tectonics

movement of portions of crust & upper mantle

• plate boundaries defined by faults

responsible for continetal movement, generation of new & recycling of old crust

Earth: only known planet w/ them

• believed essential to life

• may have started w/ solid crust, but smth hit it & broke it up

Rare Earth Hypothesis

Earth = truly rare, even in infinite universe

factors needed to establish modern life = complex & precarious

habitable zone

distance from sun where liquid water & gaseous CO2 can exist

• too close, water boils away

• too far, water freezes, CO2 condensates

  • frost line: distance from sun where heat is no longer enough to vaporize / melt water

isotopes

some heavier than others (ie. O16 vs. 18)

• ratio of light-heavy can give us information abt envral history

relative abundance reflects conditions under which a material formed

• isotopic signature

radiometric (absolute) dating

mainly from igneous rocks

• also sedimentary & metamorphic

only useful if rock hasn’t experienced chemical / physical breakdown

dated via radioactive isotopes

• half-life: radioactive decay = natural clock

• when igneous rock = formed from magma, isotopes = incorporated into the rock (clock starts)

• if half-life known, can look at ratio of parent-daughter isotopes & calculate rock age

relative-age dating & law of superposition

from relationship btwn rocks, can give approx. date range

• not as accurate as radiometric dating

law of superposition (sedimentary rocks)

• can be calibrated w/ surrounding / interspersed igneous rock layers

carbon / radiocarbon dating

shorter time frames (w/ organic life)

radiocarbon dating: same half-life principle, but clock starts when an organism dies

• measures decay of radioactive C-14

• downside: short half-life, all C-14 gone in ~50k years

asthenosphere & tectonic plate movement

asthenosphere:

• just below lithosphere (upper mantle & crust)

• temp hot enough for liquid rock

  • in liquid region, movment driven by density & temp differences

temp diff. btwn inner & outer mantles drive convection current in mantle

• move tectonic plates in 3 complementary processes:

  • push: creation of new plate at ridges

  • pull: destruction of plates at subduction zones

  • float: easy floating of solid plates over liquid base in asthenosphere

• push-pull process driving plate tectonics: creation of new plate pushes existing plate away, older plate enters subduction zone, pulls rest of plate along w/ it

  • assumed driver of entire movement

tectonic plates

large subdivisions in crust, generally in motion over long time scales

2 main types:

• oceanic

• continental

faults

major fractures in continuity of 2 rock regions

*not all faults = associated w/ plate boundaries, BUT all plate boundaries = associated w/ faults !!!

oceanic crust

density: 2.9-3 g / cm³

mostly uniform thickness: ~5km

• all relatively young on geological timescale (oldest ones formed ~280 mill. yrs ago, most much younger)

• mainly under oceans, BUT can be on land!

  • Tip of Mount Everest = oceanic crust

continental crust (& cratons)

density: 2.7 g / cm³

differences in thickness: 40-70km 

• Varying age, generally older than oceanic crust:

  • Average age = ~2 bill. yrs

  • Cratons: oldest & most stable regions of continental crust (some up to 4 bill. yrs old) 

• Generally on land, BUT can be under ocean!

  • Most of Zealandia continental crust below Pacific ocean

subduction zones

where 1 plate forced under the other

depending on crust types involved & location, different processes & landforms appear at the boundary

• usually heavier plate (often oceanic crust) under lighter one

divergent boundary

new oceanic crust forms from hot liquid rock rising from asthenosphere

• seafloor spreading

• hydrothermal sea vents & rift valleys

• magnetic pole reversals

←— —→

seafloor spreading

tectonic plates moving apart at divergent boundaries

• new crust hotter & less dense than cooler & older ones

  • seafloor rises where crust is lighter (less dense crust floats higher on the mantle, forming characteristic “ridge”

  • new crust sinks as it ages & cools

    • further from active ridge = lower elevation of oceanic crust

hydrothermal sea vents & rift valleys

weak point in sea floor where water & minerals enter ocean via geothermal heating

• common along divergent boundaries

formation on continental crust = how supercontinents eventually break up

• where continental curst = thinner / weaker, warmer rocks can break through & divide continental plate

• rift valley: divergent boundary on land

  • much rarer than oceanic ones because:

    • rocks formed at divergent boundaries = similar composition to oceanic crust (denser than continental)

    • over time, new dense crust falls below surrounding continental crust & water occupies new depression (fresh or marine water)

    • all ultimately submerge under water

magnetic pole reversals

magnetic N & S poles generated by Earth’s field switch every ~300k years

• evidenced via new rock formed at divergent boundaries

  • when rock solidifies, minerals magnetized w/in it = locked into orientation reflecting existing direction of Earth’s magnetic field

    • measuring directions can track magnetic pole reversals over time

convergent boundary

2 plates move directly towards each other, 1 forced under the other

• ocean-continent

• ocean-ocean

• continent-continent

convergent boundary: ocean-continent

ocean crust = denser, subducts below continental

• forms oceanic trench

as oceanic plate pulled into asthenosphere, melts from increasing temp

• melting rocks = less dense, rises to continental crust

  • results in volcanic activity

convergent boundary: ocean-ocean

one oceanic crust (likely older & thus denser one) subducts under other

• forms oceanic trench

subducting crust melts & produces volcanic activity

• responsible for many oceanic island chains

convergent boundary: continental-continental

one crust forced under the other, but not completely subducted into asthenosphere!

• continental crust less dense than the asthenosphere, !easily sink into it

• 2 continental plates collide: rocks forced up into new mountain ranges

  • if some oceanic crust beneath continental ones, parts can be moved to mountain tops (ie. Everest = oceanic crust)

transform boundary (& elastic rebound theory)

2 plates slide past each other

• result in characteristic transform faults

• source of earthquakes

elastic rebound theory:

• earthquakes occur bcuz plates at transform boundaries can’t continuously move (even tho it does at divergent & convergent boundaries)

• energy & pressure build up at fault until release all at once in sudden movement of both plates

tectonic boundaries facts

• interactions btwn 2 plates can involve all 3 forms of boundary movements at the same time

• a boundary can become inactive over time or form in new locations

• processes driving plate boundaries !understood

igneous rock

“fire formed” via cooling of molten rock from the mantle

• can form w/in or outside of a crust (via volcanic eruption)

• how all minerals in crust = initially formed

sedimentary rock

formed from pieces of other rocks & sometimes organic material

over time:

• successive layers built uo

• increased weight & pressure forces lower layers together into 1 structure

• new mineral forms - often has visible layers from diff materials

sedimentary rock & fossilization

where most fossils are found

• key to investigating emergence of life

• majority of organisms havenever been fossilized

• fossils usually in marine sedimentary rocks (but also freshwater)

metamorphic rock

minerals that have changed from their original form via intense heat & pressure

• elemental composition stays same, but connection btwn elements in the minerals can change depending on external pressure / temp applied

• happens under crust or at convergent boundaries

weathering

disintegration (weakening) & decomposition (break down) of rock

• leads to erosion, transport, & deposition

3 types: physical, chemical, biological

physical weathering

• Mechanical break-up of rock

• Occurs w/ & w/o terrestrial life

• Caused by water, ice, & physical contact between 2 sets of rocks

chemical weathering

• Mineral breakdown caused by chemical reaction

• Also occurs regardless of terrestrial life

• ie. water combines w/ CO2, creates weak carbonic acid that can chemically weather 

biological weathering

• Only occurred on land after life became terrestrial 

• Can seem mechanical: 

  • Tree roots breaking up rock

  • Parrotfish eating dead corals 

• Can seem chemical (ie. lichen using acids to break down rock)

  • Difference: biological component involved

erosion, transport, & deposition

Erosion: material weakened / broken down by weathering is moved from its original location

• Moved by water, wind, ice, or gravity 

Transport: Eroded material moves locations, can be very long distances 

• possible as long as energy required to move the mass is available 

  • ie. fast running water carries things further than slow running water

Deposition: occurs whenever & wherever energy to move material runs out 

• Sedimentary rocks can form over time where energy runs out (material gathers)

endogenic

exogenic

relief

geologic cycle

fluvial transport

glaciers

tides & waves

Eolian transport

rain shadow effect

meandering river systems

estuaries

deltas

alluvial fans

glacial till

homeostasis

selectively permeable membrane

heredity

ATP

universal energy currency

electrochemical potential ( / proton) gradient

polymer / macromolecule

last universal common ancestor (LUCA)

primordial soup theory

RNA world theory

hydrothermal deep sea vent theory

veterbrate

tetrapod

arthropod

common ancestor

UV light

desiccation

b

buoyancy

gas exchange

placental

m

marsupial

heterodentition

endothermy

diurnal vs. nocturnal

niche

resour

resource partitioning

character displacement

lactation

Nocturnal Bottleneck Hypothesis

megafauna

shared characters

s

sister species

evolved from common ancestor

morphological traits

physical appearance / structure / form

molecular phylogeny

reconstructing relationships w/ DNA

founder population

sexual dimorphism

selection

genetic diversity

environmental niche

allopatric speciation

paraptric speciation

sympatric speciation

hybrid speciation

gene flow

n

natural selection

mutation

genetic drift

genotype vs. phenotype

reproductive isolation

planetary requirements for life

1. ability to support liquid water (right distance from star / Sun - habitable zone factor)

1. right planetary mass

2. Jupiter-like neighbour

3. large moon

4. plate tectonics

planetary requirements for life: liquid water

habitable zone factor

water implied to be crucial to emergence of life by current life on earth

planetary requirements for life: planetary mass

right size to:

• retain atmosphere & ocean via gravitational attraction

• generate enough heat for plate tectonics

• have large mixed solid & molten core w/ metal elements that can generate a magnetic field

  • generated btwn solid inner core & liquid outer core

  • deflects winds that would strip away atmosphere

planetary requirements for life: Jupiter

right neighbours

• Jupiter formed early on

• exerts large gravitational influence

• clears out large stray bodies in early inner solar system, now fleans out comets, asteroids

  • would greatly impact history of life w/o it

planetary requirements for life: large moon

right neighbours:

• helps offset pull of Jupiter & Sun

• stabilizes obliquiy (which causes seasonal changes)

  • right amount of climate variation to stimulate evolution

  • smaller / more distant moon would not have same effect

• cause of tides - may have been v. important for early life