ES1001 Flashcards
What is Earth’s geographical column?
om locality to locality around the world, geologists have pieced together a composite stratigraphic column that represents the entirety of Earth’s visible history
Relative vs. numerical age:
The age of one feature relative to another is known as its RELATIVE AGE. The age of a feature given in years is its NUMERICAL AGE
What is radioactive decay?
When isotopes undergo a conversion into a different element (Bonus point: In half life)
What is Geochronology?
We investigate the what, when, and how of planetary-scale of a process
What is a seismic wave?
Rupture of intact rock or frictional slip along a fault produces seismic waves (and earthquakes), these move outward in all directions
What density of rock will make p-waves travel at an increased velocity?
Denser rock, such as igneous
(Example: peridotite vs sandstone)
Do seismic waves travel faster or slower in solids? In comparison to liquids
They travel faster through solids
(Example: they move more slowly in liquid than solid rock)
Can s-waves go through liquid?
both P- and S-waves can travel through solids but only P-waves can travel through liquid
When do seismic waves refract?
Seismic energy as waves will reflect and/or refract when reaching the interface between two layers of rock of differing compositions and/or densities
Define a rock
(Like no seriously…)
A naturally occurring and consolidated material usually comprised of one or more mineral phases
What rock type is igneous
Something which directly crystallised form a liquid rock (melt)
What rock type is sedimentary
Bits of other rocks in one place
What rock type is metamorphic
Cooked rocks
Why do sedimentary rocks form at or near the Earth’s surface?
Cementation of grains and/or fragments derived from pre-existing rocks
Precipitation of minerals from water solutions
Growth of skeletal material in organisms
What is weathering
The processes that break up and corrode solid rock, eventually transforming it into sediment
Physical weathering breaks rocks into unconnected grains or chunks
Chemical weathering refers to the chemical reactions that alter or destroy minerals when rock comes into contact with water solutions or air
Fun fact!!
(Lemme have fun jeez… flip!!)
Sedimentary Rocks are sometimes made of dead things
How are metamorphic rocks formed?
A rock that forms when a pre-existing rock (igneous or sedimentary) is affected by changes in its physical or chemical environment
include variations in temperature (T) and pressure (P), these changes result in the growth of new minerals and textures
What is ‘plate tectonics’
The lithosphere is divided into 15-20 plates of varying sizes
The plates move relative to each other
Explain a ‘hot spot’
Isolated volcanic centres far away from plate boundaries, many lie at the end of a chain of extinct volcanic islands and seamounts known as a hotspot track
hot spot tracks are thought to be the result of plates moving over stationary plumes
Why do we study minerals?
They make up everything, the majority of Earth, any rock is an aggregate of two or more mineral grains.
Definition of a mineral
Aka the web of lies
A mineral is a crystalline, homogenous, inorganic solid with a defined chemical composition that occurs naturally
Explain the minerals crystal structure
Their building blocks (atoms, ions, molecules) are arranged in an ordered and repeated pattern.
The unit cell is the smallest unit that still has the full symmetry of the crystal structure of a material.
Repeating the unit cell over and over again forms a crystal.
The ordered atomic network within a crystal can be simple or fairly complex.
What is a mineraloid?
Some minerals are not (fully) crystalline. These are called mineraloids.
Explain why crystals SHOULD be homogenous
Following from the infinitely repeatable unit cell of the crystal structure, minerals should by definition be homogenous
What may be the cause of a non homogenous mineral?
Zonations and crystal defects
What are the examples of an organic ‘mineral’
Biominerals - formed by a living organism usually inorganic in composition may contain organic material
Amber - fossilised tree resin organic composition
What is a polymorph?
Minerals with the same composition but different crystal structure
What is coordination?
The number of direct neighbours that an atom/ion is bonded to in a crystal structure.
Typically we talk about cations and their surrounding anion-neighbours.
What is coordination?
the number of direct neighbours that an atom/ion is bonded to in a crystal structure.
Typically we talk about cations and their surrounding anion-neighbours.
What is a site?
A space in a crystal lattice that can be occupied by an atom/ion. It is typically named by its coordination.
What is compatibility?
Atoms/ions in a crystal lattice can be substituted by other elements, as long as their radius is similar.
Ideally, their charge would also be the same! If an element fits readily into a crystal structure, it is called compatible
Nesosilicates
Island silicates
Consist of isolated “islands” of [SiO4] 4– tetrahedrons.
Sorosilicates
Group silicates
Two SiO4-tetrahedrons can share one oxygen and form a group
Cyclosilicates
Ring silicates
When a SiO4-tetrahedron shares two of its oxygen corners, we can form rings
Inosilicates
Chain silicates
Like an unclosed ring, sharing two oxygen corners creates chains
Phyllosilicates
Sheet silicates
Sheets of Inosilicates
Tectosilicates
Framework silicates
What is ‘plate tectonics’?
The lithosphere is divided into 15-20 plates of varying sizes
The plates move relative to each other
Hot Spots?
Isolated volcanic centres far away from plate boundaries
Many lie at the end of a chain of extinct volcanic islands and seamounts known as a HOT SPOT TRACK
Hot spot tracks are thought to be the result of plates moving over stationary plumes
Defniton of a mineral?
A mineral is a crystalline, homogenous,
inorganic solid with a defined chemical
composition that occurs naturally
How d minerals have a crystalline structure?
Their building blocks (atoms, ions, molecules) are
arranged in an ordered and repeated pattern.
Aka repeating he UNIT CELL
What a a mineral which isnt fully crystalline?
Mineraloid
What is a polymorh?
Polymorphs are minerals with the same
composition but different crystal structure.
How do minerals form
crystallisation of a magma due to cooling effectively the same as freezing
Magma cools below its liquidus, and starts to crystallise minerals.
The mix of melt + minerals keeps on crystallising until it ”hits” the solidus, now all melt has solidified
- Elements
Pure elements, metals often called “native”…
usually bound by metallic (in metals) or covalent bonds
- Sulphides
Minerals that have sulphur as anion.
- Halides
Minerals with halogens (F, Cl, Br, I) as anion.
- Oxides/ Hydroxides
Minerals with oxygen and/or OH as anion.
- Carbonates
… with the carbonate ion (CO3) 2- as anion.
- Borates
… with the borate ion (BO3) as anion.
- Sulphates
with the sulphate ion (SO4) 2- as anion.
- Phosphates
… with the phosphate ion (PO4)
3- as anion.
- Silicates
Form 90% of Earths crust
Si and O as anions
Building silicates
SiO4 tetrahedredreon
1 Si with 4 O- atoms
Si4+ (+) 4o^2- makes [siO4]4^4-
Neosilicates - Island silicates
consist of isolated “islands” of [SiO4]4– tetrahedrons.
Since a mineral cannot be charged, we have to balance the quadruply-negative charge.
A charge balance can be achieved by throwing cations in the mix.
nesosilicates - island silicates EXAMPLE
Olivine
achieves charge balance by adding two divalent cations per [SiO4]4– island.
It can be either Mg2+ or Fe2+
→ (Mg,Fe)2SiO4
Sorosilicaties - group silicates
Two SiO4-tetrahedrons can share one
oxygen and form a group:
2 Si4+ + 7 O2- makes [Si2O7]6-
Sorosilicates-group silicates EXAMPLES
Zoisite
Cyclosilicates - ring silicates
When a SiO4-tetrahedron shares two of its oxygen corners, we can form rings
Depending on the number of rings, we get different molecular anions, with different charges…
But always a multiple of Si4+ + 3 O2- → [SiO3]2-
Cyclosilicates - ring silicates EXAMPLES
Tourmaline, Beryl
Inoslicates - chain silicates
Like an unclosed ring,
sharing two oxygen corners creates chains
2 Si4+ + 6 O2- → [Si2O6]4-
Inosiliictes - chain silcates EXAMPLES
Pyroxenes
have two slightly different cation-sites in their lattice
M2 (larger cation site)
M1 (smaller cation site)
e.g. Augite
Amphiboles … are complicated and have a lot of cation-sites, but are a common mineral
phyllosilicates - sheet silicates
Every SiO4-tetrahedron shares three of its corner oxygens
Si4+ + 1O2- + 3*½O2- = SiO2.5 = [Si4O10]4-
phyllosilicates - sheet silicates EXAMPLES
Micas
Tectosilicates
- framework silicates
Every SiO4-tetrahedron shares all four of its corner oxygens
Si4+ + 4*½O2- = SiO2 = [SiO2]0 - No charge!
Tectosilicates
- framework silicates EXAMPLES
Quartz
is a very happy chappy,
doesn’t need any cations
to charge balance and
therefore usually is very pure.
Formula: SiO2
Composition of a mineral
Heavy element = heavy mineral (duh)
Packing
More atoms = more dense
Like more socks = more dense suitcase
Relative estimates
Colour
colour as a result of interaction with (sun)light
(Sunlight = white light
contains all wavelengths of the visible spectrum)
Colour WARNING!
Small changes in a crystal
can change the way it interacts with light.
(e.g amethyst, quartz, citrine)
Streak colour?
We can powder” a mineral by grinding it
against a hard and
rough surface, like an
unglazed ceramic tile.
Transparency
Describes whether a material allows light
to pass through.
Lustre
How a mineral reflects
Just make up your own words
Twinning
Twinning describes the intergrowth of two
(or more) crystals of the same mineral
through a slight change in orientation of
the crystal lattice.
Double refraction
Technically the majority of transparent and translucent
minerals double-refract light;
CALCITE is so very slay that u can see double
Photo - Luminescence
In some minerals, absorbing (high-energy) light results in the emission of (visible) light.
Fluorescence
The light emission stops when the
high-energy light stops
Phosphorescence
The light emission can continue for some time after the excitation stops
Magmatism
Magnetite is magnetic
Taste
Salty stuffs
Halite tastes salty.
It is table salt after all.
Sylvite tastes salty, too,
but has a bitter aftertaste.
7 crystal system SHAPES
(teigan terms dw)
Cube
Chip
Matchbox
Pencil
Triangular prism
Flattened matchbox sidey-ways
Stack of cards pushed askew in two directions
7 crystal TERMONOLOGY
cubic
tetragonal
orthorhombic
hexagonal
trigonal
monoclinic
What is metamorphism
The mineralogical and
structural adjustment of solid rocks to physical
and chemical conditions that have been
imposed at depths below the near surface zones
of weathering and which differ from conditions
under which the rocks in question originated.
What are the key factors of metamorphism
The precursor rock
Pressure
Temp
Deformation
Where does the heatcome from within metamorphism
Conduction (mantel)
Advection (magma/hot fluid)
Radioactive decay ( U, Th, K etc)
Temps of 250 to >1000°C
Where does pressure come from with metamorphism
Overlying rock mass
Horizontal tectonic forces
Pressure= fore per unit
Lithostatic pressure = density x gravity x height
Why do newminerals grow?
More stable at better conditions
Determined by thermodynamics
Thus, thermodynamics determines which collection of minerals have thelowest energy for a particular rock composition, pressure and temp
Regional metamorphism
Due to burial
Occurs with deformation
Occurs over large areas
Called belts
Shows continental collision (therefore mountain ranges)
Occurs formulations to 10s of millions of years
Contact deformation
Localised heat sources
Occurs around large igneous intrusions (dominated by heating n cooling)
Occurs oversmaller areas
Area around the intrusion is called the contact aureole
Short-lived
Hydrothermal metamorphism
Ocean floor basalts interact with hot fluids
The basalt is metamorphosed
Impact metamorphism
This occurs when you drop a huge rock from space (meteorite) onto the earth.
¨ Enormous transient pressure and temperature changes
¨ Very short lived - seconds-days
¨ Also called shock metamorphism
¨ Pressure from the impact (force per unit area)
¨ Temperature from friction
Fault related metamorphism
Related to brittle or ductile deformation in faults and shear-zones
Intense deformation allows new minerals to grow
¨ Sometimes friction can provide additional heat
Commonly associated with hydrothermal metamorphism
Metamorphic rocks are classified in general on their
appearance
¨ This is controlled by:
Composition
P and T conditions
Deformation
Features of metamorphic rocks!
Inherited features
Eg bedding in metamorphosed sediments
Eg large igneous crystals from metamorphosed
igneous rocks
Features of metamorphic rocks!
Metamorphic features
Minerals of different sizes
Features of metamorphic rocks!
Metamorphic and deformation features
Distinct layers
Aligned grains (preferred orientation)
Folds
Metamorphic fabric and structure
Layering
Alternating layers of different compositions
May include inherited features such as bedding
Foliation
A planar feature in a rock defined by the preferential
orientation of mineral grains
Lineation
A linear feature in a rock defined by the preferential
orientation of mineral grains
Crenulations
Small scale folds
Porphyroblasts
Metamorphic rocks may have some garians that
are much bigger than the average grain size
Porphyroclasts
In FAULT related rocks they are metamorphic rocks may have some garians that are much bigger than the average grain size
Phenocrysts
The big grains in igneous rocks
Matrix
The finer-grained minerals that host the
porphyroblasts are collectively referred to as
“matrix”
Matrix minerals
Individual minerals are called “matrix minerals”
Using structure no foliation
No foliation
¨ Hornfels
¨ Granofels
Using structure with foliation/lineation
Foliation/lineation
¨ Slate
¨ Phyllite
¨ Schist
¨ Gniess
¨ Layered or banded gneiss & Migmatite
Using structure- intensely foliated
Intensely foliated and sheared rocks
¨ Mylonite
What is a metamorphic assemblages
Is those minerals that appear to co-exist stably in a rock
¨ i.e it is a list of minerals
AKA Christmas rock
Garnet-clinopyroxene(omphacite)-quartz
Metamorphic assemblages are important for constraining metamorphic grade (Pressure & Temperature)
What is a metamorphic facies
any two rocks with the same chemical
composition that are metamorphosed at the same P-T conditions will contain the same minerals in the same proportion
¨ This is governed by thermodynamics
¨ We can use common rock types to define broad P-T regions based on the mineral assemblage they contain
These broad P-T regions are called metamorphic facies
Metamorphic facies can also be determined using other
rock types such as metapelites
What are the 5 main metamorphic facies
¨ Greenschist facies
¨ Amphibolite facies
¨ Granulite facies
¨ Blueschist facies
¨ Eclogite facies
What is metamorphic evolution
As metamorphic rocks occur at the surface today, they
must also experience a period of cooling after
metamorphism
¨ We can divide the metamorphic evolution into parts based on whether T is increasing or decreasing
T increasing prograde
T highest peak
T decreasing retrograde
P-T pathways
The tall, elongated, clockwise path is characterised by deep burial and exhumation with limited heating
The shorter, rounder clockwise red path is represents both substantial burial and heating
What is a metamorphic zone (zonen)
In contact metamorphism there is a strong temperature gradient away from the intrusion
¨ This results in changes in mineral assemblages away from the intrusion
What is a metamorphic isograd?
Some regional metamorphic belts show a consistent change in minerals across them.
¨ The appearance of a key mineral can be mapped in as an isograd.
Each metamorphic zone is separatrated by an isograd
Whatis continental collision in metamorphism
The most important metamorphic environment
If metamorphism occurs when continental plates collide then ancient
metamorphic belts show us how and when the continents were assembled into their current configuration
Ocean subduction I metamorphism
If metamorphism occurs in subduction zone then some metamorphic belt tell us where old subduction zones were
Metamorphic - Diverent plate boundaries
Plates move apart
¨ This is where new oceans form if the process continues
Metamorphic - transform plate boundaries
Plates slide laterally
¨ May involve a component of extension (transtension) or compression (transpression)
Metamorphic- convergentplate boundaries
Plates collide
¨ If one or both of the plates is oceanic then subduction occurs
¨ If both are continental then continental collision occurs
Orogenesis
Building mountains
Mountains represent crust/lithosphere that has been thickened
¨ Sometimes to more than double its normal thickness
¨ Thickened crust is not stable, but occurs because of tectonic forces
Mountains are controlled by isostacy (the iceberg effect)
¨ The higher the mountain the thicker the crust/lithosphere
Examples of continental collision
Alps and himalayas
Regional metamorphism - With regards to subduction
Here we have subduction causing continental collision.
There is defm & thickening due to the applied stresses
Subduction zones and island arcs
Two types
Ocean-ocean
¨ Makes island arcs
¨ Eg Japan
Ocean-continent
¨ Makes continental volcanic arcs and mountains on the continental margins
¨ Eg the Andes
These may evolve into collision zones
Subduction metamorphism
Subduction involves high pressures. SO the rocks formed in subduction zones are blueschists and eclogites
During burial and heating the rock experiences prograde metamorphism. The prograde reactions release water which enters the hot mantle.
This water can initiate melting of the mantle: also melting of the slab
can occur
Metamorphic - volcanic arcs
The large input of magma heats and thickens the arc crust
Arcs are very hot environments
Get high T at relatively shallow depths
Very high temperatures common in the lower half of arc systems
High temperature-low pressure metamorphism due to magmatic heat
Explain the biosphere structure
Living organisms (biota) and non-living (abiotic) factors from
which they derive energy and nutrients
What are the two Geobiological energy sources?
Phototrophy and Chemotrophy
What is an autotroph
Primary Producers: build organic matter by fixing carbon
Provide most organic carbon for the biosphere
Cyanobacteria
What is a Heterotrophs
Cannot fix carbon to form their own organic compounds.
Consumes organic compounds/primary producers
Energy flow in ecosystems
The biosphere is an open system with regards to energy
→ energy flow upwards in a food pyramid is inefficient, and relies on
continued primary production
What is the residence time? (Equation)
Mass of substance
————————– = residence time (10^12kg/year = GtC) of carbon
Flux (in or out of)
What is a feedback?
A feedback is a self-perpetuating mechanism of chang
What is negative feedback?
diminishes disequilibrium to maintain a steady state
What is positive feedback
enhances the effects of perturbation and drives the
system further from equilibrium.
Organic stored carbon
Terrestrial: Coal (land plants in anoxic swamps)
Marine: Petroleum in shales (phytoplankton debris)
Inorganic stored carbon
Carbonates; limestone, aragonite, chalk etc
What is geobiological weathering
Bicarbonate produced by weathering of both carbonates and silicates
The Archean (Geobiology)
Single cellular life; chemotrophs and/or non photosynthetic phototrophs
Stromatolites: oldest unambiguous fossils at 3.4 Ga. Microbial mats formed of cyanobacteria (modern examples) and interleaved sediments.
The Proterozoic (Geobiology)
True multicellularity has only ever arisen among the eukaryotes
Results in:
• Specialised cells
• Increase in size
• Increased morphological diversity
• Sexual reproduction
Whatis biomineralisation
Largely calcium carbonate plus silica and phosphate
Likely as a response to predation→ modern food webs
What waste Cambrian Explosion
Rapid diversification in body plans, particularly Bilatera
• Divergence of nearly all extant phyla
• Expansion in mode of life: burrowing, active swimming, pelagic
Mesozoic Life (Geobiology)
Rapid diversification after the P-T mass extinction
Rise and dominance of the dinosaurs! + grass + flowering plants
Cenozoic life
Loss of dinosaurs following the K-T mass extinction
Rapid diversification and dominance of mammals
The end-Permian “P-T” mass extinction
Largest know mass extinction: occurred in two
waves at ~252 Ma
~90 % of marine species and ~70 % of terrestrial
vertebrates lost
Siberian Traps: giant volcanic eruption coincident with the P-T extinction
Dust, volcanic gases (SO2; CO2), intruded into coals → Global Warming
Ocean acidification, enhanced weathering and eutrophication-induced “super”anoxia
The end-Cretaceous (“K-T”) mass extinction
Impact at Chicxulub: resulted in 180 km diameter crater.
Iridium (+other PGE) spike, shocked quartz, glassy beads (ejecta spherules)
Impacted anhydrite or gypsum → massive sulphur release
Glaciation for energy resources
Hydroelectric power from glacially fed catchments is a major source of energy
in some regions
British Columbia, Canada: >85% of electricity from hydropower, and in
summer 50% of water supplied by glaciers
What is an ice sheet
Largest masses of ice, covering huge countries or continents such as Antarctica and Greenland
Characterised by a slow-moving interior plateau and fast-moving edges forming outlet glaciers or ice
streams
1-3km thick! Melting would cause 70 m of sea level rise
What is an ice shelf
Large areas of floating ice in embayments or along the margins of an ocean basin, fed by ice streams
from a neighbouring ice sheet e.g., Antarctic margin
What is the cryrosphere
Its the frozen part of Earth and the most susceptible to
anthropogenic climate change
• Important for controlling global sea level
Whatis an ice cap
Smaller accumulations of ice covering high topography or high latitude regions, characterised by radial
flow outwards from the centre
What is sea ice?
Freezing of sea water at high latitudes
Sea ice extent has been declining in recent decades due to climate change
What is permafrost?
Freeze-thaw activity within the upper “active layer” produces patterned ground structures such as icewedge
polygons and pingos
What is patterned ground?
regular pattern of circles / polygons formed in active layer due to cyclical freezing and thawing of water in the pore spaces and frost heaving
Whatis a pingo?
Small hills of earthcoveredice that form by expansion of pore water through the active layer as a result of pressure from expanding permafrost underneath
What is a cirque (corrie) glacier
smallest – found in cirque (bowlshaped depression on side of mountain formed by glacial erosion)
What is a valley glacier?
A cirque glacier that expands outward and downward into a valley
Whatis a fjord glacier?
When a glacier valley is partly filled by an arm of the sea, the valley is called a fjord, and the glacier is a fjord glacier
Bits fall off to cause icebergs
What’s a piedmont glacier
Forms when valley glacier spreads out onto lowlands
Formation of sea ice
• Air temperature falls below freezing point of salt water
• Consists of freshwater as salt is excluded from ice crystals as they form
• First ice to form consists of small crystalline needles: frazil ice (pure H2O)
• As more crystals form they produce a viscous mixture at the ocean surface, eventually freezing together to make continuous ice cover
• Cold air no longer in contact with seawater and so sea-ice growth then proceeds by addition of ice to base
• Melting, sublimation removes ice from surface
• But loss at surface compensated by ice crystals added to the base
Sea ice Zonations
Perennial sea ice:
The sea ice that persists for multiple years
• In Arctic, just north of Resolute Bay: can be 3-4 m thick and
decades old
• In Antarctic, confined to semi-enclosed seas (Ross, Weddell): can
be 5 m thick, but <5 yr old
Sea Ice Zonations
Seasonal sea ice
sea ice cover that varies annually
• Cause of variation in extent varies between Arctic and Antarctic
• Arctic: warmer air temperatures is major factor in retreat of the ice margin
• Antarctic: warmer ocean temperatures is major factor in
retreat of the ice margin
Glacier formation - from snow to ice
Compaction by overlying snow
• Air penetrates pore space and evaporation occurs at points of snowflakes
• Moisture freezes between points, near center
• Formation of granular snow called FIRN, intermediate stage between snow and glacial ice
• Snow gradually loses interstitial air to become glacier ice
Glaciers brittle upper layer
Top 50 m of glacier is brittle –does not flow because has relatively little weight on it
• Crevasses form in top layer as glacier bends over topography (e.g., an abrupt change in slope)
• Provide a conduit for meltwater from surface to get to depth in glacier through englacial channels
• Meltwater can also percolate through firn layer
Glacier surges
Some glaciers undergo periodic surges – rapid advances
• Several kilometres per year
• May be related to buildup of water at base
Glacial erosion
Mechanisms:
• freeze-thaw at base of glacier
• abrasion
• plucking
The oceans general knowledge
Cover 70.8% of the Earth’s surface,
Contains 97% of the Earth’s water,
Have an average depth of 3.6 km.
Oceanic crust
Oceanic crust is denser than continental crust,
The light thick continental crust floats higher on the mantle than the dense thin oceanic crust
Ocean lectures - spreading and subduction
Sea floor spreading creates mid-ocean ridges
Subduction creates deep ocean trenches
What pattern is seen within nutrients in the oceans
Dissolved nutrients to support primary production are low in surface waters and
then regenerated at depth.
Impacts of ocean stratification
inhibits the vertical mixing of ocean waters, preventing dissolved nutrients being transported back to the sea surface.
Effect of mixing within the ocean
Storm mixing and tidal mixing in shelf seas breaks down seasonal stratification
How are ocean basin formed?
Plate tectonics
How are continental slopesare shelfs produced
Water overfills the basins and spills onto the continental crust
How are shelf seas important in oceanic environments
Shelf seas are important for primary production and
carbon storage
What can affect ocean circulation
Ocean features (seamounts, islands, plateau, trenchs)
What is Eckman Transport?
Eckman Transport is the deflection of surface waters in the upper 100m of the water column, as a result of the Coriolis Effect.
Surface waters are deflected 90° to the right in the northern hemisphere and 90° to the left in the southern hemisphere.
What is Grye circulation
Winds create drag on the surface waters, setting them in motion
The Coriolis effect deflects surface waters to the right in the Northern hemisphere, so oceanic gyres rotate in a clockwise direction. The opposite occurs in the Southern hemisphere.
The density of surface seawater is sufficient to cause sinking at two general locations:
The North Atlantic
The Weddel Sea (Southern Ocean)
Together, temperature and salinity drive the thermohaline circulation of the oceans
How can we detect water masses?
Depth profiles of temperature and salinity
What can drive surface currents?
Wind
Whare does the Coriolis Effect divert current
To the right in the N Hemisphere and the left in the S Hemisphere
How do deep ocean waters form?
From high density waters
Wind generated gravity waves:
Wind stress creates small ripples in the water’s surface. Now there is a pressure difference between the front and back of the wave.
The front face is sheltered from the wind and experiences a lower air pressure than the back face, which faces the wind. This pressure difference pushes the wave along.
Importance of waves
Water mixing (e.g. shelf sea stratificationSustainable energy sourceShipping hazardErosion/deposition of sedimentsSea level changes
What is an amphidromic point?
Points with no tide
What is a Guyot?
A flat topped volcanic mountain
What is a Seamount?
Underwater mountain (usually volcanic)
Implications of sea level change
Changes in shelf sea area affect primary production, ecosystem distribution, carbon transport etc.
Changes in sea level affect tidal dynamics in shelf seas and the global ocean
What is tidal dissipation
The loss of the energy of tidal i.e. moon generated, waves
How can we reconstruct sea level?
Using the and age of fossil coral reefs
What are the common marine pollution issues
Metals
Organic chemicals
Oil
Contaminants of emerging concern
Nutrients
Plastic
Noise
How are PBCs in the Marianas trench?
These PCBS are probably incorporated into particulate material at the ocean surface which then sinks to the ocean bottom to deliver the contaminant.
What is a Roche Moutonnee
Rock formation created by the passing of a glacier.
The passage of glacier ice over underlying bedrock often results in asymmetric erosional forms as a result of abrasion on the “stoss” (upstream) side of the rock and plucking on the “lee” (downstream) side
Erosional Glacial features
Striations and chatter marks
Striations: Produced by small rock fragments embedded in basal ice that scrape away at the underlying bedrock and produce long parallel scratch marks
Chatter marks: A series of often crescent-shaped gauges chipped out of the bedrock as a glacier drags rock fragments underneath it
Corries!!
Among the most common and distinctive landforms
produced by glacial erosion
Bowl-shaped valley formed at glacier head
Coire Sgorach on Sgurr a’ Mhaim is a classic northfacingcorrie eroded by a small cirque glacier high on the mountain face during successive glaciations of Scotland
U shaped valleys
Originates in a corrie, U-shaped (duh)
Higher geo
Aretes
Sharp-edged, narrow ridge of rock separating two valleys
Formed when two oppositefacing glacial cirques erode headwards towards each other
Also formed when two valley glaciers erode parallel Ushaped valleys
Edge is sharpened by freezethaw weathering, and slope is steepened through mass wasting events and erosion
Svalbard!
Glacial horns / pyramidal peaks
Pointed pyramidal peaks formed from cirque erosion due to multiple glaciers diverging from a central point
A classic example is the Matterhorn in the Swiss/Italian Alps
A Scottish example is Carn Mor Dearg
Hanging valleys
Tributary valley well above main valley floor: typically formed when main valley has been widened and deepened by glacial erosion, leaving the side valley
abruptly cut off from main valley
Steep drop-off usually creates dramatic cascading waterfalls
Coire a’ Mhail and Coire Giubhsachanare both hanging valleys, with steep drops at the end into
Glen Nevis below
Glacial erosion mechanisms
freeze-thaw at base of glacier
abrasion
plucking
Till
Sediment deposited directly by a glacier is neither sorted nor stratified
Heaps of poorly sorted sediment called till are left as glaciers abate
Outwash
Till can be then reworked by meltwater streams that
transports it beyond terminus of glacier where it is deposited as outwash
Moraines
Ridge-like accumulations of till are moraines
Form as sediment is bulldozed by a glacier advancing across the land
End moraines form at the terminus of a glacier, with the terminal moraine marking its furthest advance (Longyear glacier, Svalbard)
Lateral moraines form at the sides (Lars, Svalbard)
Medial moraines form where two glaciers join
Moraines are important tools that scientists use to determine the extent of ice coverage during an
ancient glaciation
Drumlins
Ice sheets mold oval hills called drumlins
Drumlins are elongated parallel to the direction of
ice flow
Formed by glacial ice acting on underlying unconsolidated till
Streamlined hills shaped beneath the ice
Common in the central lowlands of Scotland, between Glasgow and Edinburgh
Eskers
Rivers flowing beneath ice (subglacial channels) leave
ridges of wellsortedsand and gravel called eskers
Kettles
Shallow, sediment-filled body of water formed by retreating glaciers or draining floodwaters
Form as a result of blocks of ice calving from glaciers becoming submerged in the sediment in outwash plain, which then melt to produce a void filled by a
sediment-rich lake
Landscapes marked by kettles, now typically occupied by lakes, ponds, or wetlands are clear evidence of previous glaciation
Kames
Kames are an irregularly shaped hill or mound
comprised of piles of sand, gravel, and till that
accumulates in a depression on a retreating
glacier and is then deposited on the land
surface with further melting of the glacier
Marine ice sheets
The Marine Ice Sheet needs to be heavy (thick) enough to displace the water to be grounded.
Ocean warming can melt the ice sheet faster than it moves out to sea thinning the Ice Sheet.
Marine ice cliff instability
Positive feedback whereby the cliff face can become unstable if not supported by the
buttressing effects of ice shelves
Leads to rapid ice margin retreat
Isostatic rebound - mantle movement
Viscous mantle flows away from depressed crust under the huge weight of a mountain chain
What is a rock?
Crystals of one or more minerals bound together in a
mixture
Pumicevs pyroclastic
pumice –very frothylight-colouredcellular rock, full
of interconnected gas bubbles
pyroclastic rock formed from fragments of chilled
magma pyroclastic = fiery fragments
Decompression (adiabatic) melting
Mid-ocean ridges
Decompression melting forms
mid-ocean ridge basalt (MORB)
Continental rifts
e.g. East Africa
Over time, will become an ocean
Mantle plumes
e.g. Hawaii
Both increased heat flow and
decompression
Forms ocean-island basalt (OIB)
Volatile-assisted melting
Changing the chemical composition of the system
If you add volatiles to Earth’s mantle (H2O, CO2) you lower its melting temperature
Explain cooling time regarding texture n Grain size
More cooling time means:
-coarser
-larger grains
What is a porphyritic
A fine matrix with larger crystals
Batholith
Huge mass of intrusive rock made of
numerous plutons
Dyke
Vertical igneous intrusions to layering
Sill
Horizontal igneous intrusions to layering
What is a felsic rock
High silica content
Lighter in colour
What is a mafic rock
Low silica content
Darker rocks
What is bowens reaction
Mafic minerals crystallise First
Felsic are last to
Remaining melt becomes more felsic
Yet it can also work in reverse
Mid ocean ridges- constructive margin - igneous
Melting style
Opening of plate boundary above mantle creates void = mantle moves up to fill void
Melting occurs via decompression
Subduction zones- destructive margin- igneous
Melting style
Hydration of mantle above subducting plate
Melting occurs via volatile introduction (flux melting)
Mt. Fuji
Continent - Continent collision - igneous
Source of (original) melt: crust
Sediments, metamorphic rocks, igneous rocks
Often melt is too viscous and deep enough in crust, so it does not escape
Forms granite plutons/batholiths
Continental rift - igneous
Melting style: decompression
Source of (original) melt: mantle
Majority of melt is mafic
Some remelting of crust produces
felsic volcanoes –BIMODAL volcanism
Flood basalts
Vast eruptions of basaltic lava
Associated with the initial impingement of a mantle plume under a plate – often continental
Can start the breakup of continents – start rifting by weakening/thinning the plate
HUGE fissure eruptions of basalt
What is a lava flow
molten rock that moves over the ground
What is a pyroclastic debris
fragments blown out of a volcano
What is volcanic gases
Expelled vapor and aerosols
What determines magmatic flows
- Composition of melt
- Crystal content
- Gas content
- Temperature
Physical properties of magma
Temperature
Increasing temperature decreases the viscosity
Crystal content
The present of crystals in a melt acts to increase the viscosity of a melt
Gas content
If the gases are dissolved, the will act as network modifiers (decrease viscosity)
If the gases exsolve, they will form bubbles which act against the flow
Volcanic gas
Magma composition often controls gas content.
• Felsic magmas have more gas; mafic magmas less.
• Gases are expelled as magma rises (P drops).
• Style of gas escape controls eruption violence.
• Low viscosity (basalt)—easy escape; effusive eruption
• High viscosity (rhyolite)—difficult escape; explosive release
• Gas bubbles in rock are called vesicles.
Lava flow (viscosity) depends on:
• Composition, especially silica (SiO2) content.
• Temperature.
• Gas content.
• Crystal content
Effusive lava flows
Mafic magma – low viscosity, efficient degassing
Andesitic magma – medium viscosity
Rhyolitic magma – high viscosity, does not flow – forms domes
Basaltic lava flows
Mafic lava—very hot, low silica, and low viscosity
• Basalt flows are often thin and fluid.
• They can flow rapidly (up to 30 km per hour).
• They can flow for long distances (up to several hundred km).
• Most flows measure less than 10 km.
• Long-distance flow facilitated by lava tubes.
Andesitic lava flows
Higher SiO2content makes andesitic lavas viscous.
• Unlike basalt, they do not flow rapidly.
• Instead, they mound around the vent and flow slowly.
• The crust fractures into rubble, called blocky lava.
• Andesitic lava flows remain close to the vent.
Rhyolitic lava flows
Rhyolite has the highest SiO2; is the most viscous lava.
• Rhyolitic lava rarely flows.
• Rather, lava plugs the vent as a lava dome.
• Sometimes, lava domes are blown to smithereens.
Volcaniclastic deposits
Volcanoes often erupt large quantities of fragments.
Volcaniclastic deposits include:
• Pyroclastic debris—lava fragments (of all sizes) that freeze in air.
• Preexisting rock—blasted apart by eruption.
• Landslide debris—blocks that have rolled downslope.
• Lahars—transported as water-rich slurries.
Pyroclastic debris
Explosive eruption:
Melt, crystals and ‘country’ rock (lithic) fragments are fragmented
fragmented = blasted apart
…and blown from the vent
Explosive eruptions - felsic
Andesitic or rhyolitic eruptions
• More viscous magmas; more volcanic gases
• Less easy to de-gas = more prone to explode
• Explosive eruptions generate huge volumes of debris.
• Pumice—frothy volcanic glass
• Ash—fragments less than 2 mm in diameter
• Pumice lapilli—angular pumice fragments
• Accretionary lapilli— rounded clumps of ash forming in moist air
Pyroclastic eruptions
Different eruptive styles
Pyroclastic fall (ash or tephra deposit)
Pyroclastic flows
Pyroclastic surges
Pyroclastic eruptions
Fall
Fallout from an eruptive column/cloud
Falls like snow – mantles topography
Pyroclastic eruptions
Flow
Avalanches of hot ash (200oC to 450oC) that race downslope.
Moving up to 300 km per hour, they incinerate all in their path.
Immediately deadly; they kill everything quickly.
Many historic examples: Mt. Vesuvius, Mt. Pelee, Mt. St Helens
Block and ash flows - Ignimbrites welded by heat of flow
Pyroclastic eruptions
Surges
Like a pyroclastic flow, but denser (wetter)
Very energetic eruptions
Generally colder, lots of water
Incoming energy flux
Earth receives more energy from sun (electromagnetic waves)
Seasons due to Earth’s xis rotation causing a tilt
30% of solar energy is affected by albedo effect
Outgoing energy flux
Earh has an approximate energy balance, energy is returned as blackbody radiation
Stefano- Boltzman law:
ōT⁴ W/m²
(ō is a constant)
Earth’s energy budget
Atmosphere and ocean move because equator receives more energy from sun than it emits
Combining incoming and outgoing radiation
To close earth’s energy budget, the atmosphere and ocean need to move energy from low latitudes to high lattitudes
Energy/heat transport
We must transport polewardsas we receive more at equator
What does hydrostatic balance tell us
Pressure decreases with altitude at a rate dependant on temperature
What does geopotential height depend on
Depends on the temperature integrated between the surface and that level
Air density with temp
Warm air is less dense
Chemical composition of the atmosphere
78% N2, 21% O2, 0.93% Ar and others
Ideal gas law
p = pRT
Water saturation in atmosphere
When air cannot hold any more water vapor, its saturated , to get air to condense and firm mist, fog, clods and rain, it must cool to saturation
Atmospheric phenomena
We want to understand this for fundamental scientific discoveries and practical purposes
What is an easterlies wind??
Comes from east
What is an westerlies wind??
Comes from west
What is an notherlies wind??
Comes from north
Volcanic rock types at the rock and spindle
- Intrusive - igneous, fine grained basalts
- Bedded tuffs - pyroclastic deposits, fallen back into vent
- Tuffisite, ash rich veins that never got to the surface
Sedimentary rocks
formed on or near Earth’s surface via erosion, deposition and lithification of sediment transported by water, ice and wind or precipitated out-of-solution by biotic and abiotic processes
Classification of sedimentary rocks
clastic: composed of fragments (clasts) of pre-existing
minerals/rocks (i.e. a source area or provenance)
non-clastic: (bio)chemically precipitated
clastic rocks and non-clastic rocks commonly occur together
Classifying clastic sedimentary rocks
conglomerate versus breccia: both consist of gravel-sized sediment but their grain shapes are different, rounded vs angular, respectively
weathering and erosion of ‘parent’ rocks determines
composition of resulting sediment
intensity, duration and ‘style’ of sediment transport
processes determines the texture of the sediment
Concept of ‘maturity’
As sediment undergoes increasing intensities and durations of weathering and transport, it begins to ‘mature’:
•mafic minerals and feldspars breakdown into finer particles and clays
•quartz becomes more and more enriched
•sediment becomes better sorted and grains more rounded
Evolution of sedimentary rocks
Source (provenance)
Weathering and transport
Site of deposition
Lithification occurs and the resulting sedimentary rock is classified based on its composition and texture
Non clastic sedimentary rocks
non-clastic sedimentary rocks are precipitated by organisms or abiotically
temperature, salinity, water chemistry and sediment flux (needs to be low) influence precipitation
chemical sediments are good indicators of environmental conditions
there are numerous types of (bio)chemical sediments:
coal, carbonates, evaporites and siliceous precipitates
The order that mineral salts precipitated by (increasing) evaporation
Calcite
Gypsum
Halite
Potassium
compositional classification of (bio)chemical sedimentary rocks is typically based on the major anion
carbonates (CO3-)
CaCO3 – calcite (aragonite polymorph is metastable); forms limestone*^
(Ca)Mg(CO3)2 – dolomite; forms dolostone*
Fe2CO3 – siderite
*can form abiotically or biotically
^fizzes with weak HCl (acid)
compositional classification of (bio)chemical sedimentary rocks is typically based on the major anion
sulphates (SO4-2); commonly termed evaporites
CaSO4•2(H2O) – gypsum
CaSO4 – anhydrite
compositional classification of (bio)chemical sedimentary rocks is typically based on the major anion
Others include:
Fe2O3 – ironstone (iron oxide)
SiO2 – chert (flint; opal is SiO2•nH2O)*
NaCl – halite
*can form abiotically or biotically
limestones and dolostones: textural classification
characterised by their allochems (grains)
• bioclasts (fpieces of fossils)
• ooids – small spheres
• peloids – fecal pellets
• intraclasts – eroded clasts
and their interstitial autochem material (kinda like matrix)
• lime mud or micrite (micro-crystalline
calcite)
• cement as coarse carbonate crystals
(spar)
Ooids are an allochem
Graded bedding (sedimentary)
deposition due to decreasing flow energy results in graded bedding: coarser grains at the base of beds and finer grains upwards
(Reverse grading is also a thing)
Bedding scale (sedimentary)
layering <1 cm thick is termed laminated
layering 1 – 10 cm is termed thin bedded
layering 10 – 50 cm thick is termed medium bedded
layering 50 – >100 cm thick is termed thick to very-thick bedded
Bedform (sedimentary)
a morphological feature formed by the interaction between a flowing fluid (water, air) and sediment on a bed
bedforms inform about flow energy and transport direction
Ripples n’ dunes
ripples have h <4 cm, dunes have h > 4 cm
ripples and dunes inform on direction of sediment transport
ripples and dunes often occur together
Fluid flow and bedforms
sediment is carried up the stoss side of a ripple by the flow
at the crest, the flow separates from the bed and grains cascades down the lee side
flow ‘reattaches’ in the trough causing erosion and that sediment is transported up the stoss-side of the next ripple
the progressive cascade and migration of grains forms cross-bedding
Bedform stability and flow energy
when sediment is transported, it becomes organised into stable bedforms (e.g. ripples, dunes) that reflect flow ‘energy’ (velocity) acting on a particular grain size distribution
generally, as flow velocity increases, the stable bedforms are:
flat beds –> ripples –> dunes –> plane beds –> antidunes
by recognising bedforms, and changes in bedforms through a sedimentary sequence, you can reconstruct past flow conditions and sediment transport direction
Types of flow n ripple symmetry
unidirectional flow generates asymmetric/current ripples
oscillatory flow generates symmetric/wave ripples
Formation of wave ripples
wind shear generates waves
waves on the surface generate a circular motion (‘orbitals’) of water molecules
orbitals decrease in size downward; in shallow water these can intersect the seafloor and friction causes the circular motion to become elliptical
the horizontal motion of the ellipse at the bed can move sediment and generate symmetric ripples
Imbrication
a depositional fabric in which clasts align and overlap one another, much like a run of toppled dominoes
Soft sediment deformation
these form due to gravitational instabilities via loading and by excessive shear stress
sedimentary environments: fluvial
characteristic features of fluvial deposits:
• point bars (m-scale lateral accretion surfaces)
• crevasse splay sands (flat, tabular beds)
• overbank or floodplain mud and fine sand
• fining-upward trend from gravel in channel, sand in point bar to mud in floodplain/overbank
sedimentary environments: shorelines and deltas
• coastal zones are the interface between marine and non-marine settings
• areas where wave, tide and storm energies are dissipated
• sinks for products of physical (sediment) and chemical (ions) weathering
• zones of mixing between fresh and saline waters
foreshore or swashface
• cm- to dm-thick sets of low-angle laminae
• symmetric (wave) and flat-topped ripples
• bioturbation (burrowing)
sedimentary environments: marine settings (focus on carbonates)
controls on patterns and characteristics of deposition in marine settings include:
• physical processes such as waves, storms and tides
• oceanic conditions such as bathymetry (shelf, slope, abyssal plain), salinity and water temperature (the latter two are latitudinal or ‘climatic’)
• tectonic setting such as passive vs active margins
Carbonate reef distribution
low to no siliciclastic flux
• warm temperature (20˚- 30˚ C)
• shallow water depth (<10 - 20 m)
• average to high salinity (34.4 ppm)
Components of the climate system
The greenhouse effect
The carbon cycle
Forcing mechanisms and feedback
Climate variation
The atmosphere is made up of:
Troposphere
Stratosphere
Outer atmosphere
Drivers of climate change
Geological time-scales – millions of years
Movement of the solar system through the galaxy ~ changes in cosmic ray flux and galactic dust
Influence cloud formations
- Plate tectonics – movement of continental plates
Affects on ocean currents - Mountain building etc etc
Affects on atmospheric circulation
Weathering
Presence/absence of sea ice/ice sheets at poles
Albedo affects
Multiple feedbacks in the system
The hadean eon
Formation of Earth: 4.6 Gya
50-70 Mya later, a Mars-sized object collides with the Earth and the Moon is formed
first 600 My of Earth’s history
Sun was 30% fainter than at present
formed with no “primary” atmosphere, but outgassing resulted in an atmosphere which was likely
water vapour, CO2, ammonia, methane, hydrogen sulphide, sulphur dioxide + others
no O2 at that time
zircons show oceans and continental material had formed by 4.4Gya (0.1Gya after formation)
A planet under seige
Impacts occurred from formation through until the Late Heavy Bombardment (about 3.9Gya)
Sterilizing impacts probably occurred 6-12 times during the Hadean
No real idea what the “temperature” of the planet was at this time
The Archean
3.9 to 2.5 Gya
Oldest rocks on Earth from this period
Evidence for lack of Oxygen
Witwatersrand gold ore (~3 Gya)
Detrital Pyrite (FeS2)
Was not oxidized during weathering
Evolution of life: 3.7 – 3.5 Gya
Evolution of methanogens (prokaryotes) [cannot survive with free oxygen]
CO2 + 4 H2 → CH4 + 2 H2O
Archean ends with rise in global oxygen levels
Evolution of cyanobacteria (eukaryotes) – 2.8 Gya (earlier??)
Tectonics different to today
Higher heat flow
Smaller plates (proto-continents) and many hot spots
Temperatures likely warmer than today
Oxygen isotopes in Archean rocks suggest oceans twice as warm as today’s tropical oceans (~50oC).
This is contentious – but climate was WARM
But this is odd as the Sun was less bright!
The Faint sun paradox
No Atmosphere? - The Earth should have been “frozen” for the first two billion years
3.8 Gya: Sun’s luminosity 75% of present value
Yet – during the Archean liquid water was prevalent on the surface
In fact the geological and palaeoclimatic record strongly suggests Earth has maintained a “moderate” climate throughout its history – BUT WITH WOBBLES
The Greenhouse Effect!!!
CO2 - supplied by volcanoes
CH4 - Also from volcanoes - but also requires life - Methanogens!!
Hydrolysis
Main chemical weathering mechanism that removes atmospheric CO2
Reaction of silicate minerals (CaSiO3) with carbonic acid (H2CO3) to form clay minerals and dissolved ions
CaSiO3 + H2CO3 –> CaCO3 + SiO2 + H2O
Atmospheric CO2 combines with water = H2CO3
This process accounts for 80% of the CO2 removal
CO2 also dissolves in sea water etc
Later life – photosynthesis etc etc
Controls on weathering reactions
Chemical weathering influenced by
-Temperature
Weathering rates double / 10oC rise
-Precipitation
H2O – required for hydrolysis
H2O increases as temperature increases
Vegetation [not relevant for Archean]
Respiration in soil increases CO2
CO2 in soils 100-1000x higher than atmospheric CO2
Other factors
land formation, mountain building, latitude location etc
Organic haze
If CH4 becomes more abundant than CO2, an organic haze begins to form
Haze from UV photolysis (decomposition) of CH4
Creates an anti-greenhouse effect
Haze absorbs sunlight in the stratosphere and radiates energy back to space
E.g. Titan
Archean/Proterozoic transition
A time of significant change
Change from “small plates” to modern large plate tectonics
Significant rise in O2 due to [evolution] increase of cyanobacteria (blue green algae)
Photosynthesis
Cyanobacteria: 2.8 Gya (possibly evolved 3.8Gya)
Stromatolites
Layered Cyanobacteria accretionary structures
Implications of increased oxygen
Disrupted the balance
Solar luminosity – low but increasing!
CO2
CH4
+ water vapour
Increased weathering - oxidation
Decrease CO2
Methanogens outcompeted (?) by cyanobacteria – decrease CH4
1st major glaciation 2.3 – 2.2 Gya
It did not take much to shift the planet into a glaciation
2.2 Gya to 750 Mya
Tectonic style changed
Small to large plates
First supercontinent
Rodinia: 1 Gya – 750 Mya
Bulk of land: mid-latitudes
Related Grenville Orogeny
750 - 580 Mya
Neoproterozoic Snowball Earth: Cryogenian
Multiple periods of severe “global” glaciation
Lots of geologic evidence of low latitude glaciation
Global temperatures plunged and the whole planet was encased in ice
Or in “Slushball” alternative – tropics were ice free
Mechanics to a snowball state
Neoproterozoic Snowball Earth: Cryogenian
Multiple periods of severe “global” glaciation
Lots of geologic evidence of low latitude glaciation
Global temperatures plunged and the whole planet was encased in ice
Or in “Slushball” alternative – tropics were ice free
How to get out the icehouse
It’s the Greenhouse Effect again
Volcanic activity and carbon dioxide release would NOT have ceased during Snowball periods
Due to cold conditions, weathering rates were low so hydrolysis rates low and therefore little “scrubbing” of CO2 from atmosphere
Phanerozoic consists of 3 eras
Paleeozoic
Mesozoic
Cenozoic
Early Phanerozoic
Started with the Cambrian Explosion
A direct response to the late Proterozoic Snowball Earth
Quick evolution from “Ediacaran” fauna
Initially marine
Rapid evolution
“empty planet” - many open ecological niches
driven by predation
competition for “food” resources
Phanerozoic climate
Large swings from “greenhouse” to “icehouse” conditions
Understanding this long-term variability in global temperatures is not straightforward
Underlying hypothesis
CO2 is the main driver of global climate change
Faint sun less of an issue now
Myriad of feedbacks
Presence/absence of continents at poles
Presence/absence of ICE at poles
Hydrolysis: carbonate-silicate cycle
Cambrian
540 - 490 mya
CO2 ~ 4500 ppm, 16x pre-Industrial
Snowball build up
O2 ~ 63% of present
Temp ~ 21°, 7° above present
Sea level 30-90m above present
No ice cover
No terrestrial life
Trilobites dominant in oceans (became extinct at end of Permian)
Slow removal of CO2 through Hydrolysis
Devonian
415 - 360 mya
CO2 ~ 2200 ppm, 8x pre-Ind.
O2 ~, 75% of present
Temp ~ 20°, 6° above present
Sea level 180-120m above present
No ice cover
Land has some plants and animals
Continued removal of CO2 through Hydrolysis
Carboniferous
360 - 300 mya
CO2 ~ 800 ppm, 3x pre-Industrial
O2 ~ 163% of present
Temp ~ 14°, 0° above present
Sea level 80-120m above present
Land is dominated by swamps and forests
Some ice cover – south pole
Permo-Carboniferorous glaciation
Since the “Snowballs” of the late pre-Cambrian, one of the most extensive glacial periods in earth history until “recent” glaciations of the Cenozoic
Devonian to Carboniferous
Super continent at poles: Pangea/Gondwana
Tropical mountain range
Decreasing CO2
Permian
300-250 mya
CO2 ~ 900 ppm, 3x pre-Industrial
O2 ~ 115% of present
Temp ~ 16°, 2° above present
Sea level >60m to <20m present
Pangaea diverse climate states
Cold dry at southern polar latitudes
North – intense and great seasonal variation
Worst extinction event in Earth’s history
95% of species disappeared
Permian- triassic extinction
The boundary of the Permian and Triassic
~90% of all species died out
95% of species in oceans
Marine invertebrates – worst hit!
Took place over a 5-10 million year period
Slow start – rapid by end
Impact event (Nickel-rich Layers
From impact or heavy-metal rich mantle-derived lavas)
Volcanism (Flood basalt events
The Siberian Traps (also another in China) )
Final complete state of Pangaea – extreme climate states
Climate Change – hot or cold (or both?)
Mesozoic era
The emergence of the dinosaurs
Predatory reptiles
Amphibians living on land and in water
Reef Building corals
Climate and CO2 levels relatively constant
Triassic
250 - 200 mya
CO2 ~ 1750 ppm, 6x pre-Industrial
O2 ~ 80% of present
Temp ~ 17°, 3° above present
Desert conditions prevail, leads to success of reptiles
Late Triassic – emergence of dinosaurs
Jurassic
200 - 145 mya
CO2 ~ 1950 ppm, 7x pre-Industrial
O2 ~ 130% of present
Temp ~ 16.5°, 3° above present
High CO2, largest terrestrial animals ever
Landscape dominated by coniferous forests and fern plains
Cretaceous
145 - 65 mya
CO2 ~ 1700 ppm, 6x pre-Industrial
O2 ~ 150% of present
Temp ~ 18°, 4° above present
By end of Cretaceous CO2 levels are approaching Cenozoic levels
Another extinction event which wiped out the dinosaurs
Emergence of flowers and associated insects
Diversification of mammals
Cenozoic era
Mammals increased in numbers and diversity
Grasses and flowering plants expanded on land
Ocean life remained relatively unchanged however
The Eocene-Paleocene is the last “warm” period in Earth history
Early Eocene seen as a “worst case” analogue for where today’s change in climate, as influenced by anthropogenic CO2 emissions, could go………….!!
Eocene
55 - 35 mya
CO2 ~ 385 ppm, 1.5x pre-Industrial
O2 ~ 100% of present
Temp ~ 19°, 5° above present
BUT within this period were some significantly extreme climate states
Paleocene-Eocene Thermal Maximum
End of Eocene marked beginning of current icehouse climate
Drivers of climate change
External and Internal
External to climate system
Orbital variations, tectonic effects, sun’s variations
Internal to climate system
Feedback mechanisms
Ocean/atmospherics interactions
Ocean conveyor belt
El Nino-southern oscillation, Monsoons etc
Milankovitch cycles
- obliquity (tilt)
It is this tilt that results in the planet having seasons.
The larger the angle, the larger the difference between summer and winter - eccentricity
How oval it is - pressession
The spinning of the earth its self
All whilst spinning around the sun
Ice sheet changes with climate change
As ice sheets form, global albedo increases
Results in a further temperature drop and ice expansion
Expanding ice sheets result in a fall in global eustatic sea-level
Makes it easier for ice to flow out from the land
Further increasing albedo
These mechanisms could explain some of the added cooling not explained by Milankovitch theory
But still not enough
CO2 and the role of thermohaline circulation
Acts as a pump transferring CO2 and nutrients from the surface to the deep ocean
Carbon–plankton relationship
Phytoplankton take up CO2, falls to ocean bottom when dead
Released through oxidation – BUT deep oceans are anoxic
returned to the surface when the thermohaline circulation is on
If circulation slows – carbon is not returned to the surface – global cooling
Changes in strength of circulation would also alter energy transfer from equator to poles – especially in N Atlantic (Gulf Stream looses energy)
Self regulating negative feedback loops within climate change
Extra ice at poles should cause more downwelling
exclusion of salt from water in ice formation
Increased sea salinity – therefore denser
Causing strong thermohaline circulation
Colder climate means less terrestrial biological activity – therefore more atmospheric CO2
Colder climate means less moisture vapour in atmosphere
less precipitation to feed glaciers
Moisture vapour also a greenhouse gas
Ice cores
Ice cores
High resolution palaeo archives
Greenland
~130,000 yrs
Antarctic
~800,000 yrs
Greenland data
Shows very rapid
climate change
The youngest dryas
The last short major cold event
During the transition from the last glacial into the present Holocene
Occurred from 12,800 and 11,500 yrs ago
General warming trend interrupted by cold reversal
The late holocene
Good quality high resolution proxy data
e.g. tree-rings, ice cores, corals, speleothems, historical archives
“reasonable” knowledge of the climate over this period
Reasonable records of solar and volcanic forcing as input parameters in climate models
Last 150 years – anthropogenic period
So called “Anthropocene”
