GEOS101

Earth system

complex set of feedbacks that maintain planets climate in more-or-less stable equilibrium and maintain climate in state compatible with continuation of life

System

entity made up of different, but related, interacting parts that function as a whole

Reservoir

Part of the system that holds or stores materials or energy within the system

Flux

Flow of materials or energy between reservoirs of the system

Equilibrium

Condition where the system is unchanging in time, or only changing within narrow limits (dynamic)

Perturbation

A temporary disturbance of the system

Forcing

A sustained, persistant influence on the system that results in long term change

Gaia hypothesis

Earth is best seen as a homeostatic, self-organizing, self-regulating system

How is earths stable equilbrium maintained

By fluxes - biogeochemical and feedback loops

Geological time

fundamental clock used to asses rate and timing of geological processes

Fossil

Any trace of an organism which is (usually) preserved in rocks

Evolution

changes in morphology or behaviour between generations

Natural selection requirements

1. constant struggle for survival

2. over-abundance of offspring

3. variable populations

4. some mechanism for passing on beneficial changes to the next generation

Homologies/homologues

body parts on different organisms which share a similar position and/or structure, reflecting a common evolutionary ancestor

Analogues

body parts on different organisms that have similar functions and superficial resemblance of structures and have different evolutionary origins

Earths crust %

• 98% made up of 8 elements

• 74.3% is silicon and oxygen

• 95% is silicates

Stenos three principles

1. principle of superposition

2. Principle of original horizontality

3. Principle of original lateral continuity

Principle of superposition

In any layered sequence of rocks, any layer is older than the one above it

Principle of original horizontality

Layers resulting from particles deposited under the influence of gravity are originally parralell to the surface of the earth

Principle of original lateral continuity

Layers, when they were originally formed, are laterally continuous unless they terminate against another solid substance

Agents of metamorphism

• heat

• pressure

• chemically active fluids

Low grade metamorphic rocks

parralell alignment called slatey cleavage

200^oC

Medium grade metamorphic rocks

Mica minerals form and align to give foliation called shisctocity

400^oC

High grade metamorphic rocks

coarser grained with porphyroblasts

700^oC

Greywacke bedrock deposition

• 220-200mya

• deposited by submarine avalanches off coast of gondwanaland

• layers of sandstone and aggrilite

• slightly metamorphised

Greywacke erosion

• between 100 and 5 mya, land eroded to a peneplain and submerged beneath ocean and marine sediments

Greywacke uplift

In the last 1myrs, tectonic forces iniated uplift

Theory of plate tectonics

motions of lithosphere and accounts for most tectonic activity

• 7 major and several minor plates

Lithosphere

• crust and uppermost solid mantle

• 0-100km thick

Rocks in uppermost solid mantle

full of iron and magnesium

Athenosphere

mechanically weak layer along which tectonic plates move

<1% liquid melt
temperature of 1300^oC at athenosphere lithosphere boundary

What is the athenosphere composed of

periodite (Mg, Fe)₂SiO₄

Mantle convection

slow movement of mantle rocks caused by convection currents carrying heat from core towards crust
occurs in athenosphere and rest of mantle below lithosphere

Mantle

lies between liquid outer core and think outer crust

Outer core

only liquid layer
made primarily of iron and nickel

site of violent convection resulting in geodynamo

Earths magnetic field

outer core is geodynamo, creating magnetic field which protects earth from solar winds and cosmic waves

Inner core

composed mainly of iron

solid due to pressure

temperature of 5200^oC

Differentiation in Earths composition

Natural process by which substances settle according to density
Earth becomes more dense with each layer

Pangea

Supercontinent 200-300 mya

Supercontinent

continental landmass comprising of most of all continental crust (>75%)

Break up Pangea

late triassic

formed Laurasia and Gondwana

Laurasia

North America, Greenland, Europe and Asia

Gondwana

South America, Africa, India, Antarctica, Australia and Zealandia

Rift

divergent plate boundary, forms when 2 plates are moving away from each other

• continental rift (on continental crust)

• mid ocean ridges (new oceanic crust forms)

Crust thickness and density

Oceanic crust thickness is 6-10km and is more dense

continental crust thickness is 35-40km and less dense

Subduction

occurs at convergent boundaries, tectonic plate carrying thinner, denser crust sinks into mantle beneath overriding tectonic plate.

Collision

Occurs at plate boundaries where both plates are continental, results in thicker continental crust and mountain ranges

Transform boundaries

plates slide past each other on transform faults

Aotearoa plate boundaries

• alpine fault

• puysegur subduction zone

• hikurangi subduction zone

Alpine fault

transform fault with Australian plate continental crust and pacific plate continental crust

Puysegur subduction zone

where Australian plate oceanic crust subducts beneath pacific plate continental crust

Hikurangi subduction zone

where Pacific plate oceanic crust subducts beneath Australian plate continental crust

Trench

long, narrow depression in the seafloor that forms in subduction zones

Elastic rebound theory

elastic (recoverable) strain gradually accumulates on either side of a locked fault interseismically
- strain exceeds faults strength, stored strain energy is released by rapid localsied displacement along the fault in an earthquake

post seismically, rocks return to original state

Seismic cycle

concept used to study and describe events happening before, during and after an earthquake

Earthquake occurs when . . .

2 parts of the lithosphere suddenly move past each other, releasing stored energy as seismic waves

Stress (pressure)

= force/area
Determined by orientation and (relative) magnitude of principle stresses

Main types of fault

• reverse

• strike-slip

• normal

Seismometer

Instrument which records signals (shaking) generated by earthquales, volcanic eruptions and explosions

Seismic waves

elastic body waves, how earthquake energy is released

P-waves

• primary waves

• can travel through solids, liquids and gases

• travel by alternatively compressing and expanding material parallel to direction they are travelling

S-Waves

• Secondary waves

• only travel through solids

• travel by causing material to move back and forth perpendicular to the direction they are travelling - causing higher amplitude

surface waves

• only travel through solids

• love waves

  • move material horizontally

• rayleigh waves

  • move material elliptically

Local magnitude (M_L) Richter scale

measurement made by comparing the amplitude of shaking recorded by a seismometer with the amplitude of a reference event

Moment Magnitude M_w

Uses seismic moment to calculated moment magnitude.
Seismic moment product of shear modulus, rupture area, and averaged displacement.

Modified Mercalli (MM) Intensity scale

characterizes earthquake intensity at a location by considering impacts on people, structures and landscape.

Isoseismal

lines connecting places where earthquake was experienced with equal intensity

Seismic hazards

any physical phenomana associated with an earthquake which have potential to produce loss of life, property or income

Primary seismic hazards

ground shaking and permanent ground displacement (surface rupture hazards)

Secondary seismic hazards

tsunamis, landslides, soil liquidification and floods

Natrual hazard

atmospheric, water-related or geophysical processes or phenomana that may negatively impact human life, property or toother parts of the environment

Natural disasters

hazardous events in which people, cities and/or regions are overwhelmed by environmental conditions that exceed their capacity to cope

E-tech minerals

minerals used in electronics and other technology
many identified as critical minerals or strategic minerals

Critical minerals and strategic minerals

Metals and non-metals at risk of supply disruptions due to geological scarcity, geopolitical issues, trade policy or other factors, and/or are important to a country’s economy or defense

Key metals

• copper

• lithium

• rare earth elements

• polymetallic nodules

Key non-metals

• silica sand

• aggregate

Geochemical reservoirs

coherent regions of mass characterized by a distinctive composition

geochemistry

formation, evolution of, and interaction between geochemical reservoirs

geochemical fluxes and reservoir interactions

Element transfer between different geochemical reservoirs

• weathering

• volcanic emmissions

• sedimentation

Major geochemical perturbations

• volcanic activites

• human activities

Free oxygen percentage of modern atmosphere

21%

Free oxygen percentage of 1st ½ of earth history

<0.001%

Evidence of rise of free oxygen

primarily from biogeochemistry of sediments
elements have different solubility if free oxygen is present

Great oxidation event

2.4-2.1 billion years ago

• transitional interval of biospheric oxygenation

• dynamic balance of early oxygen production and concurrent oxygen sinks

• inferred to be caused by cyanobacteria photosynthesis

What were the oxygen sinks

O₂ does not accumulate, reacts with iron in anoxic seas and oxidises methane in atmosphere

Snowball earth

late proterozoic ice ages thought to be so extreme to perhaps have covered surface of planet from poles to equator

Evidence for extensive ice cover

• glacial deposits in tropical latitudes

• carbon isotope variations

How snowball earth occured

Intense tropical weathering of the crust led to CO2 drawdown

Led to a runaway ice-albedo feedback loop

How did earth leave deep freeze

Volcanic outgassing building CO2 levels up

Led to warming and glaciers melting,

CO2 dissolved into seawater, combined with Ca and Mg ions → thick packages of carbonate roc

Why are there volcanoes

they are mechanisms for heat and mass transfer from earths interior

Earth heat sources

• primordial (core)

• radiogenic (mantle)

Primordial heat

Heat in the core leftover from the original accretion of the Earth
Makes up just under half of Earths heat budget

Radiogenic heat

Primarily coming from the solid (but convecting) mantle

Produced by decay of radioactive isotopes

Makes up just over half of Earths heat budget

Conduction

Diffusive transfer or energy from one body to another

• in inner core

Convection

Transfer of energy by fluid motion combined with diffusion

• outer core and mantle

Advection

Transfer of energy by fluid motion without diffusion

• crust

Where are volcanoes

• divergent margins

• convergent margins

• intraplate = hot spots

Divergent margin - mid ocean ridges volcanoes

As plates spread apart primitive basaltic magma rises and erupts to fill the gap

• eg ocean + iceland

Convergent margin - subduction zone volcanoes

Subducting slab is subject to melting

melt ascends because of low density

create wide vareity of magma types

• eg taupo volcanic zone

Intraplate hot spot volcanoes

anomalous mantle plumes

tectonic plates move overhead resulting in island trains

mostly basaltic

• eg hawaii