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Planet Earth and the Biosphere
01 October 2014

11:34

Key physical aspects of Earth affecting life
Covering:
• Geosphere
• Atmosphere and climate
• Hydrosphere
• Biogeochemical cycles
• Pedosphere (soil)
• Feedback between abiotic and biotic

Biosphere Page 1

John Scullion
Life on Earth
• Goldilocks zone
○ Sustain life
○ Liquid water - 0-500C and atmospheric pressure
○ Varies with star
• Earth's internal structure and formation
○ Formation:
 Earth heats and melts
□ Cataclysmic events
□ Radioactive elements
 Differentiation
□ Random chunks began to layer
□ Denser elements sank
□ Less dense crust floats and cools
□ Gases escape to form 'atmosphere'
○ Inner and outer core
 4400-61000C
 Spinning creates magnetic field
□ Protects from solar radiation
□ Formed 3
...
037%
• Formation:
○ H2, H2O, NH3, CH4 evolved
...
4bya
○ Photosynthesising algae put O 2 into the atmosphere
○ Further increase in O2, decrease in CO2 due to carbon fixing and
oxidation
○ 3
...
45bya very little oxygen, 2
...
85 oxygen produced but
absorbed in sinks, like the oceans
...
85-0bya sinks filled, gas
accumulated in atmosphere
○ Steady increase in oxygen
 Mass extinction of anaerobic organisms
○ Free oxygen reacted with methane, removing its insulation
 Glacial period

Quaternary climate
• Cyclical temperature fluctuations
• Glacial and interglacial periods
• Astronomical cycle, changes in atmosphere, tectonic
effects on ocean currents etc
...
e
...
6ppm
• Mainly in lower stratosphere
• Thickness varies seasonally and geographically
• Absorbs 97-99% of UV-b
○ Damaging
○ At low levels helps produce vitamin D
○ Higher concentrations damage DNA
• Southern hemisphere ozone hole phenomenon
○ Lowest concentration over Antarctic in Southern Spring
○ Polar vortex excludes circulating ozone
○ Conditions favour ozone depletion

Biosphere Page 2

Temperature
• Evolving atmospheric composition
• Greenhouse effect
○ Methane, N2O, CO2
• Past concentrations have been greater than present
• Without them Earth would be much colder

Hydrosphere
07 October 2014

10:12

Hydrological Cycle
96% of water in oceans
0
...
nutrient rich Humboldt
○ Affects global weather systems
 Floods and droughts/monsoons
• Gulf stream
○ NW flow of warm warer, affecting Eastern USA and Western Europe
○ Compensating Greenland current cools South Eastern Canada

Evolution of life in oceans
• Early Earth - bombardments vaporised
surface
• Relatively stable physiochemical
environment
○ Osmotic pressures fairly
consistent
○ Solution of organic molecules
formed under reducing
conditions, in atmosphere or
near hydrothermal vents
• Ready access to water
• Some protection from solar radiation
• Moderation of temperature extremes
• Anoxic environment
○ Early organism produced oxygen
as a waste product, but fixed
chemically

Water and life
• Critical to survival
• Habitat covering 71% of Earth
• Variations in osmotic pressure affect
loss/gain of water
• Some organisms can use salt water
• Majority need access to fresh water
• Accessible freshwater <1% total

Fresh, Ocean, and Coastal Salinity
• Salinity fairly stable
• More variable in coastal regions
○ e
...
Estuaries
• Salinity due mainly to transport of salts from land
• Differing densities
○ Fresh water less dense
○ Mixing limited

Classification
Fresh

Brackish Saline

Brine

<0
...
05-3

3-5

>5

Parts per 1000 <0
...
5-30

30-50

>50

Conductivity

300-180
00

18000-30000 >30000

% Salt

<300

Factors
• Evaporation
○ Salt left as water evaporates
• Proximity to freshwater
• On geological timescales:

Biosphere Page 3

Variations in physiochemical properties
• Geographical variations
○ Biological demand
 Depth has strong influence on diversity
○ Solubility
• Thermocline
○ Marked temperature changes
○ Limited mixing
• Depth
○ Photic zone - light primary energy zone
○ Aphotic zone - detritus or hydrothermal vents
○ Pressure at 10m = 2x atm
...
4k =
500kg/cm2
○ At the surface there much variation
 High demand for chemicals
 Much more stable at depth
○ Dead/anoxic zones

Factors
• Evaporation
○ Salt left as water evaporates
• Proximity to freshwater
• On geological timescales:
○ Ice build up
 Ice mostly salt free
○ Ice melt
 Influx of fresh water

500kg/cm2
○ At the surface there much variation
 High demand for chemicals
 Much more stable at depth
○ Dead/anoxic zones
 Too many nutrients from fertilisers etc
...
As pH will fall, carbonate levels will fall as
the carbonates dissolve
□ 3% decline 1700 - 1990
 Loss of organisms
□ Coal growth rates will decrease/go into regression
 Increased carbon dioxide
• Currently net sink for atmospheric CO2
• Arm surface waters less able to hold gases
○ Oceans warming
 Less oxygen also
• Decomposition at depth
○ CO2 enrichment
○ Biological pump
• Cold water upwellings release CO2
• Sequestered in sediments as carbonates/shell debris
○ Acidification breaking them down

Conclusions
• Limited freshwater
• Life's cradle
• Currents distribute heat and
nutrients
• Variations in nutrients and
oxygens with regions and
depth
• Important regulator of
atmospheric carbon dioxide
○ Riding temperatures
○ Acidification

T

Biosphere Page 4

Pedosphere
08 October 2014

11:07

Soil
• Very thin
• Rarely >1m in temperate zones
• Key biosphere services
○ Plant growth
○ Habitat
○ Regulator of water flows and quality
○ Important interactions with atmosphere
• Soil product of pedosphere interactions between geosphere, atmosphere and hydrosphere

Evolution of soil
• Mineral particles and decomposed organic matter organised by living compounds
• Before life colonised land soil didn't exist
○ Bare rock or unstable products of weathering or erosion water and nutrients lost quickly
• Cyanobacteria first to colonise
• Lichens important colonists
○ Break down of rocks - oxalic acid waste
• Soil formation accelerated by higher plants and burrowing animals - Ordovician
• Symbiotic associations between plants and nitrogen fixing bacteria
○ 100mya in Eurosid clade of plants
○ Much more efficient
• Co-evolution of terrestrial plants and mycorrhizoid fungi
○ 400mya
○ Marked increase in nutrient scavenging

Soil Genesis
• Soil profiles slowly deepen and develop
characteristic horizons, until a steady
state is achieved
• Surface processes such as erosion leads
to a dynamic system
• Upper horizon properties dominated by
biota
• Lower horizon properties dominated by
physiochemical weathering

Humus Formation
• Labile organic compounds into
stable forms
• Dead materials decompose,
yielding carbon dioxide, water
and humus
• Composition of detritus affects
processes/rate
• In circumeutral soils rapid
decomposition and distribution
by earthworms - Mull humus
• In acid soils slower distribution
and more iron leaching - Mor
humus

Habitat
• 1/4 to 1/3 of all organisms - only 1% identified
• 5 tonnes of animals per hectare
• Most terrestrial ecosystem processes that sustain life ○ Soil fertility
○ Nutrient cycles
○ Greenhouse gas fluxes
○ Pollution control
-are driven by soil biology
• Soil communities underpin above ground habitats
• Complex habitat
○ Differing depth ranges leads to diversity

Interactions
• Devonian
○ Trees abundant
○ Carbon dioxide removal
○ Absence of lignin digesters
○ Reduced greenhouse effect - ice age
○ Fungi decomposing lignin restored some
balance
• Enhanced activity by tree roots meant more
weathering, releasing calcium and adding to
sedimentation
• More leaching of nutrients causing eutrophication
of oceans

Mineral weathering
• Physical
○ Freeze thaw
○ Warm-cold exfoliation
• Chemical
○ Primary (feldspars and micas) to secondary
(kaolinite, illite) minerals
 Very slow - time and climate
○ Hydration, hydrolysis, dissolution, acid-base,
redox
• Biological
○ Roots
○ Organic acids and complexing agents

Moisture regimes and soil genesis
• When evapotranspiration < precipitation in
permeable media
○ Leaching and podzolisation
○ Chlorine, nitrates, sulphates, carbonates, lost
from surface horizons
○ Base cations replaced by acid cations
 Acidification
○ Clay migration and degradation
• Evapotranspiration < precipitation in impermeable
media
○ Waterlogging
○ Gleying (loss of Fe)
○ Organic matter accumulation
• Evapotranspiration > precipitation
○ Salination and sodicity
○ Net upward movement of water and salts,
especially with shallow groundwater
○ Accumulation of soluble salts

Soil and global warming
• Major store of carbon and methane
• Reaction to changes - source or sink?
○ Warming will lead to increased SOM decomposition
○ Elevated carbon dioxide will mean increased carbon inputs
• Seasonal moisture regimes complication
○ Rainfall changes hard to predict
• Cryosols
○ Permafrost melting and releasing methane
• Histolsols
○ Accumulated partially decomposed SOM
○ Major proportion of carbon and northern latitudes may warm
more quickly

Soil forming factors
Parent material
• Primary minerals
○ Nutrients -> vegetation productivity -> extent
of quality of humus formation
○ Base cation contents
 pH and buffering potention
□ Acidification dissolves minerals,
making the soil more alkaline again
• Grain size and stability
○ Soil texture and permeability
○ Variations in leaching potential

Topography
• Geomorphological processes
○ Erosion
○ Differentiation of particle size
• Hydrological characteristics
○ Proximity to water table
○ Salt build up
○ Shedding or receiving sites
• Aspect
○ Microclimates moderate climate influences
Climate
• Effective precipitation
○ Depth of water penetration
○ Transportation of soluble and suspended
materials
• Higher temperature saccelerates weathering
• Cold climate
○ Shallow soils
• Both factors affect rates of carbon fixation in plants
Biota
• Wide range of pedogenetic processes affected
• A-horizon development
○ Organic matter inputs va root systems and
surface residues

Biosphere Page 5

surface residues
○ Broadleaf vs conifers
 Broadleafs more effective at recycling
base cations - Mull humus
○ Nitrogen accumilation via fixation or lightning
• Soil animals
○ Ecosystem engineers such as earthworms and
termites
 Bioturbation militates against distinct
horizonation
Time
• Organic accumilation A-horizon over 10-20 years
• Discernable changes in B-horizon 40-50 years, full
development over centuries
• Accumulation of silicate clays over millennia
• 2cm of topsoil can take >500 years
• Timescales depend on process rates
• Major differences between temperate regions
affected by glaciation and tropical areas

Biosphere Page 6

Biogeochemical Cycles
14 October 2014

14:41

Carbon and nutrients flow between biotic and abiotic components
Gaseous
• Global
○ Nitrogen
○ Oxygen
○ CO2

Alterations to the cycles cause problems
Eutrophication
Global warming

Liquid
• Medium for plant uptake of nutrients
• Major reservoir for elements such as carbon and conduit for recycling into
geosphere

Carbon Cycle

Solid
• Pedosphere (local) and geosphere (regional) variation
• Main source of mineral elements for organisms

Terrestrial Carbon Cycle
• Difference between carbon fixed by plants and released through
respiration is the net primary productivity (NPP)
• In most natural ecosystems NPP is balanced by decomposition
• Peatlands
○ Ongoing sinks of carbon
○ Millennia of accumulation
○ Global warming is tipping them from sink to source
• Agriculture
○ Carbon removed in harvests, but losses slow for grazed systems

Decomposition
○ Breakdown of organic matter by consumers
 Fungi, bacteria, and detritivores
○ Converts organic compounds into carbon dioxide
○ Fungi and bacteria convert dead organic matter into inorganic
nutrients for primary producers
○ Final outcome is mineralisation
 Carbon dioxide via respiration to atmosphere
 Ingorganic compounds and elements to soil and water
○ Decomposition curve
 Half-life
 Progressively harder materials to decompose are produced
 Depends on
□ Resource quality
□ Environment
□ Time to 95% decomposition
 Stages
□ Rainwater leaches soluble compounds
□ Organic matter fragmented by detritivores
□ Fungi and bacteria metabolise smaller fragments and
mineralise organic substrates
 Rates of decomposition
□ Simple compounds rapidly metabolised
□ Lignocellulose has a high C:N ratio
 Fungi degrade woody tissues by lignases, H2O2,
and cellulases
 Slow
□ Simple compounds may be physically protected by
structural compounds
 Cycling rates
□ Warm and moist
 High productivity and rapid decomposition
□ Cold or dry
 Slower cycling
 NPP > decay
□ Swamps and marshes
 Oxygen levels low so slow decomposition
 Build-up of partially decayed matter over
geological time
□ Feedbacks
 Plants decay at different rates
 Changes to soil type
 Different plants can grow
 Resource quality
□ Decomposition rates dependent on C:N ratio
□ High quality have low C:N
 7:1 in most tissue
 200:1 in wood
□ C:P can be important
□ As decomposition progresses, resource quality
improves with release of carbon dioxide and
conservation of nutrients
○ Decomposer organism
 All heterotrophs
□ Digest and break down organic molecules
 Decomposer usually refers to smaller organisms, mostly in
soil
 Majority of decomposition
 Fungi
□ Extracellular enzymes and hyphal growth penetrate
and digest complex, polymeric, solid substrates
 Detritivores
□ Earthworms, nematodes, springtails, woodlice

Overall Respiration = Photosynthesis

In the oceans phytoplankton are
responsible
CO2 + H2O <=> H2CO3
H2CO3 <=> H+ + HCO3-

Ocean pH has changed from 8
...
14
since 1750

Biosphere Page 7

Studying cycles
• Radiocarbon 14C
○ Useful label, but problematic in
the field
15N 13C can be used to label systems
•
and to follow their fates
○ Present in nature in low
abundance

Anthropogenic impacts on carbon cycle
• Land use changes
○ Deforestation
 Rainforests
 Conversion to agriculture in
Europe
○ Grassland or 'arable'
○ Stripping of surface soil
• Fossil fuel consumption
○ Recycling of geosphere CO2
• Forest clearance = 1/3 of anthropogenic
CO2
• Cultivation of forest and grassland soils
increases mineralisation of soil carbon
up to 70 tonnes/hectare
• Increased erosion leads to loss of soil
carbon into hydrosphere

□ Earthworms, nematodes, springtails, woodlice
 >200/m2
 120 million nematodes per metre2
□ Contribute 10% to soil respiration
□ Mainly physical effects
 Increase surface area for attack
 Mix materials
□ Regulate microbial activity (grazing)

Biosphere Page 8

Cryosphere
15 October 2014

11:56

80% of our biosphere is permanently cold
<4 degrees C

Cryosphere and Climate
• Albedo
○ Light surfaces reflect more pf the sun's energy
○ Average temperature on Earth
As present: +15 degrees
No ice: +27 degrees
Entirely ice: -40 degrees
○ Enthalpy of fusion
 Energy must be [ut into ice to convert it to water before temperature can rise
 To increase the temp of 1kg of ice by 20 degrees
□ From 10 to 30 = 80kJ
□ From 0 to 20 = 415kJ
○ Global climate models predict amplified warming over poles
• Amplification
○ Positive feedback
 Ice-albedo feedback
□ Less ice, less albedo, more warming
 Even small changes can cause thawing/melting of ice structures
 Arctic ice retreating
□ Albedo lowered

Typically water is in the frozen state
Plays major role in Earth's climate

Life in the cryosphere
• Challenges
○ Cold
○ Extremes
 pH
 Salinity
○ High UV
○ Complete darkness in polar night
○ Short growing seasons
• Animals
○ Humans
 Cold injuries
□ Hypothermia
□ Frostbite
 Survival
□ Avoidance
□ Insulating clothing
□ Eat more calories
□ Special sleeping gear
□ Shivering
○ Other mammals
 Fur
□ Camouflage
□ Insulation
□ Highest insulation:thickness
ratio of any fur
 Countercurrent blood exchange
□ Hot blood passes heat onto
cold blood
□ 10oC feet, 37oC core

Biosphere Page 9

□ 10oC feet, 37oC core



 Eat a lot
○ Cold blooded animals
 Tardigrades
□ <1mm
□ 8 legged
□ Aquatic
□ Can be boiled, frozen
□ Cryptobiosis
 Desiccate themselves
◊ 1-3% water
 Trehalose and glycerol
as antifreeze
 Rotifer
□ Repair chromosomes by
adding DNA to telomeres
□ DNA repair mechanisms allow
serious damage
• Plants
○ Tiny
 High surface area to volume ratio
○ Waxy leaves
• Microbes
○ Active even at low temperatures

Biosphere Page 10

Glaciers
16 October 2014

•
•
•
•

13:17

Huge mass of ice
Slowly flowing
Accumulation must be greater than ablation for a number of years
Flows due to stresses induced by its own weight

For glaciers to form there must be persistent snow
Accumulates
Compresses beneath own weight

Types
• Valley glacier
• Tidewater/marine terminating glacier
• Cwm glacier
• Hanging glaciers

Accumulation > ablation = advance

Water doesn't freeze until -40 degrees when pure and sterile
...

 This allows hydrogenotrophic
methanogenesis
□ CO2+4H2 --> CH4 + 2H2O
 For average bacterium, fewer than 2000
carbon atoms per year are enough

Movement
• Basal slippage
• Pressure melting point of water
• Accelerates glacier
• Plucking and abrasion

Microbes and the Glacial Mass Balance
• Snow has high albedo
○ Cryoconite lowers albedo
○ More heat absorbed
• Cryoconite
○ Full of microbes
 DNA and chlorophyll
visible
○ Dust colonised
○ Pigments produced as
sunscreen, darkening ice
○ Pothole formed
• Accelerated glacial melting

Biosphere Page 11

Chemical and microbial weathering
Greenland
• 4 factors
• Ice sheet holds 2
...

Sea ice vs ice shelves
• Sea ice - frozen seawater
• Ice shelves - glacial ice pushing out
Importance to ecosystems
• Biological productivity and albedo has far
reaching impacts

• Cold freshwater is denser than freshwater ice
• Salinity increases water density
• Freezing point is lowered by salinity increasing
○ It's harder for oceans to freeze, but easier for ice to float on them

Iron Cycle
• Iron deficiency limits the abundance of life in polar
oceans, despite abundant nutrients
• In Antarctic iron must come from glacial runoff, rather
than Aeolian dust
○ Lots of debris carried by glaciers
• Icebergs also carry a lot of material
○ More icebergs --> more iron --> more productivity
○ Negative feedback against global warming as
calving speeds up

Sea Ice
• Growth

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Biosphere Page 14

The Cryosphere's Past
28 October 2014

10:10

Finding past climates
• Dendrochronology
○ Wood from 1670 has tighter grain than that from the 20th century
○ Shorter growth periods
○ Needs wood though, so limited scale
• Glacial Ice
○ Glacial ice accumulates in layers
○ Ice columns can be 3km deep
○ There are 9 isotopes of water
 1H - 99
...
016%, 3H - produced by nuclear explosions
 16O - 99
...
04%, 18O - 0
...
g
...
T/U = pyruvate
○ Codon position 2 corresponds to solubility
...
Only very few, more
recent, amino acids use it
RNA world
• DNA
○ Encodes information
○ Cannot catalyse reactions
○ Needs proteins in order to replicate
• Protein
○ Catalyse reactions
○ Cannot encode information
○ Needs DNA for synthesis
• RNA
○ Encodes information
○ Catalyses reactions
○ Intermediate in protein synthesis
 May be original genetic material
○ Assembles into polymers at high concentrations
○ Breaks down into nucleotides at low concentrations
• Alkaline vents
○ Thermal gradients
 Currents through pores
 Concentrate RNA
○ Thermal cycling
 Promotes RNA replication
 PCRish
• Spiegelman's monster
○ RNA in a test tube
○ Evolves to maximise replication efficiency
 Short chains
 From any starting point
 Minimal sequence
○ Not what we want for complex life
 Must be group competition
 More energy and proteins to help are pressured

Origins of Cells
• Prokaryotes
• Earliest living cells
• 2 main types
○ Eubacteria and archaea
 Different cell walls
 Different cell membranes
 Different DNA replication enzymes
□ Did living cells evolve twice?

The Prokaryotic World
04 November 2014

10:20

The Precambrian
• Before explosive diversification
• Archaean Era
○ 4
...
5bya
• Proterozoic Era
○ Palaeoprotozoic - 2
...
6bya
○ Mesoprotozoic - 1
...
g
...
g
...

◊ Prevent mound formation
 Present day stromatolites
◊ Restricted to protected habitats
 Low nutrients
 Few grazers due to hypersalinity
Anaerobes
○ Dominated early Earth
○ Respire without oxygen
○ Great Oxidation Event
 Excluded anaerobes from much of Earth
 Survive in anaerobic pockets
□ Anoxic muds
□ Animal guts
○ Methanogens
 Archaea
 Hydrogen and carbon dioxide to methane
□ No hydrogen where there's free oxygen
 Outcompeted for hydrogen by sulphate reducing bacteria
 Only survive where oxygen and sulphur are absent
□ Bottom of freshwater lakes
□ Stagnant marshes
□ Guts of herbivores and vegetarians
Dispersal of prokaryotes
○ Extremely small
○ Very widely dispersed
○ Cosmopolitan hypothesis
 No geographical boundaries to dispersal
 Everything is everywhere, the environment selects - de Wit & Bouvier, 2006
Do they speciate?
○ DNA transferred laterally between distantly related individuals
○ If only horizontal transfer then yes
○ But hard to apply species concept when DNA can be transferred laterally
Can they go extinct?

Biosphere Page 18

Photosynthesis
• Great Oxygenation Event
○ Cyanobacteria
○ Iron started rusting
• Until 2
...
8-0
...

• Paradox
○ Mitochondria require oxygen to survive
○ Methanogens cannot survive in the presence of oxygen
○ Hydrogenosomes
 Organelles of anaerobic eukaryotes
 Related to mitochondria
 Release hydrogen
□ Feed methanogens
□ Could have been original 'invader'
○ Anaerobic mitochondria
 Close relatives to aerobic
 React alternative compounds to release energy
○ Common ancestor
 Hydrosomes, anaerobic and aerobic mitochondria
□ Shared ancestor
□ Metabolically diverse
□ Later specialised
○ Hydrogen hypothesis
 Hydrogen generation alpha-proteobacterium
 Associated with methanogen
 Eventually moved inside (endosymbiosis)
 Methanogen absorbed food
 Alpha-bacterium produced hydrogen
 Methanogen used hydrogen
 Methanogen evolved ATP transporter
□ Stole energy
□ Could survive aerobically
 Arguments
□ Disputed methanogen ancestor
 Other interpretation of data somewhere
□ Cell membrane more similar to bacteria than archaea
□ Archaea cannot engulf bacteria

Biosphere Page 21

Multicellularity
11 November 2014

10:12

Prokaryotes
• Potentially immortal
○ All cells can proliferate
○ Do not age
• Individual cells
○ Can change genetically
○ DNA uptake and loss
• Asexual
○ Entire genome inherited as a unit
○ Natural selection
 Cannot act on individual genes
 Cell is the unit of selection
• Differentiation
○ Evidence from 3bya
○ Genetically identical cells
 Perform different functions
□ e
...
cyanobacteria (genetically identical)
 Resistant spores
 Sticky biofilms
 Floating blooms
□ "Algal" blooms
 Cyanobacteria
 Related to stromatolites
◊ Float
 Proliferate into vast blooms
◊ Persist for weeks
◊ Suddenly disappear
 Programmed cell death in response to threats
◊ Viruses
◊ Radiation
 Cells of bloom
◊ Identical
◊ Most die
◊ Some healthy cells persist as spores

Biosphere Page 22

Single-celled eukaryotes
• Potentially immortal
• Individual cells
○ Do not age
○ Do not tend to change genetically
• Meiosis
○ Destroys genome
 Chromosomes reassort and recombine
○ Death
• Syngamy
○ Cells fuse
○ Form new genome
• Natural selection
○ Can act on individual mutations
 Within genomes
• Colonial organisms
○ Cells cooperate
 Enhances survival and reproduction of colony
○ Limited cell specialisation
 Limited complexity
○ No distinction between germ line and soma
 Any cell can produce a new colony
 e
...
volvox, sponges
○ Algal colonies
 True algae
 Eukaryotic
 Some form spherical colonies
□ Exterior cells
 Specialise for mobility -flagella
□ Interior cells
 Resistant spores
 Individual cells can still live independently
○ Slime moulds
 Amoeba like
□ Exist independently
 Under stressful condition they aggregate and mate
□ Form mobile, coordinated plasmodium 'slug'
□ Able to continue feeding
 Fruiting body
□ Some cells form stalk
 Do not reproduce
 Sacrifice for other cells to reproduce
□ Other cells form spores

Multicellular organisms
• Divided into germline and soma
• Only germline reproduce
• Somatic cells benefit
○ All cells are identical
• True multicellularity
○ Separate germline and soma
 Policed by apoptosis
□ Somatic cells killed if they attempt to
proliferate independently
 Evolved multiple times
□ Red algae
□ Brown algae
□ Plants
□ Animals
□ Fungi
○ Sexually reproducing eukaryotes
 Individual has finite lifespan
 Sex scrambles genome
□ Genes inherited independently
 Only genes survive death of the organism
□ Transmitted to new organisms
 Organisms are vehicles to genes
□ The gene is the unit of selection
• Genes and cells
○ Genes
 Code for proteins and DNA
□ Manufacture cell components
 Do not code for structure
□ Membranes
 Formed by division and growth of
existing membranes
□ Mitochondria
 Formed by growth and division of
existing mitochondria
□ Centrioles
 Organise cytoskeleton
 Only formed from existing centrioles
 Can only function within existing cells
○ Cells
 Require genes to survive and reproduce
○ Genes do not make cells
 Only cells make cells

Cancer
• Usually occurs through accumulated mutations
○ Oncogenes
 Stimulate division
 Become permanently active
○ Tumour suppressor genes
 Suppress division
 Cause apoptosis
 Become inactive
○ Growth factors
 Stimulate blood vessel growth
 Feed tumours
○ Digestive enzymes
 Break down surrounding tissues
 Allow tumour to invade
• Metastasis
○ Cells must
 escape tumour
 Evade immune system
 Bind to blood vessels
 Burrow into new tissue
 Halt and resume proliferation
• Cancer cells
○ Evolve by natural selection
 Each mutation
□ Increases replication rate
□ Provide competitive advantage within individual
○ Doomed
 They destroy the individual
 Cannot escape
 Transmissible cancers are the exception
□ Devil Facial Tumour Disease
 Tasmanian devils
 Transmitted by biting and aggressive
courtship
□ Canine Transmissible Venereal Disease
 Infects dogs
 Affects genitalia
 Sexually transmitted

Apoptosis
• Programmed cell death
○ Cells die
○ Consumed by immune system
• During development
○ Sculpting of tissues
• In developed organisms
○ Removes old cells
○ Removes cancer cells
 Prevents independent proliferation
• Caspases
○ Proteins
○ Bring about apoptosis
○ Mitochondrial origin
○ Activated by mitochondrial gene products
 Remnants from a parasitic relationship?

Sex and death
• Damage to DNA can prevent replication
• In prokaryotes
○ Repaired through DNA uptake
○ Provides new genetic material
○ Damaged DNA eliminated
• In single-celled eukaryotes
○ Repaired through sex
○ New genetic material
○ Damaged DNA eliminated
• In multicellular eukaryotes
○ Repaired through apoptosis
○ Cells with DNA damage killed
• Similar signals from mitochondria cause sex and apoptosis

Aging
• Peter Madwar
○ Statistical likelihood of death
 Disease, predation etc
...
(1993) - genetic evidence
Ancestral Chl --> BChl --> Chl
○ Lockhart et al
...
An understanding of the origin and evolution of photosynthesis is therefore
of substantial interest, as it may help to explain inefficiencies in the process and point the way to attempts to
improve various aspects for agricultural and energy applications
...
Figure
1shows an evolutionary tree of life based on small-subunit rRNA analysis
...
The ability to do photosynthesis is widely distributed throughout the bacterial domain in six different
phyla, with no apparent pattern of evolution
...
5 type from which both evolved
○ Gene duplication resulted in two similar proteins, which
differentiated
• Two theories for the two systems (cyclic and non -cyclic) developing
○ Fusion hypothesis
II, I --> II+I
○ Selective loss hypothesis
II+I --> II, I
○ (Blankenship RE Plant Physiology 2010; 154: 434 -438 http://www
...
org/content/154/2/434
...


(purple bacteria), green sulphur bacteria (GSB), firmicutes (heliobacteria), filamentous anoxygenic phototrophs
(FAPs, also often called the green nonsulfur bacteria), and acidobacteria (Raymond, 2008)
...


View larger version:

• In this page

• In a new window
• Download as PowerPoint Slide
Figure 1
...
Taxa that contain photosynthetic representatives are highlighted in colour, with green
highlighting indicating a type I RC, while purple highlighting indicates a type II RC
...
Tree adapted from Pace (1997)
...
So the evolutionary

Carbon fixation
• Photosynthesis drives the conversion of water and CO 2 to carbohydrates
and oxygen
CO2 + 2H2O + hv --> O2 + [CH2O]n
• Calvin-Benson cycle
○ All oxygenic photosynthesis
• Early Life
○ Evolution of oxygenic photosynthesis played pivotal role in evolution
○ Evolution of autotrophic CO2 fixation around 3
...
, 2002)
...
In addition, the recent explosive growth of
available genomic data on all types of photosynthetic organisms promises to permit substantially more
progress in unravelling this complex evolutionary process
...
In this brief review we will discuss the evolution of photosynthetic pigments, reaction centres (RCs),
light-harvesting (LH) antenna systems, electron transport pathways, and carbon fixation pathways
...
However, to a
significant degree they can be considered as modules that can be analysed individually
...
There have been numerous suggestions as to where and how the
process originated, but there is no direct evidence to support any of the possible origins (Olson and Blankenship, 2004)
...
2 to 3
...
In all these cases, phototrophs are not certain to have
been the source of the fossils, but are inferred from the morphology or geological context
...
7 to 3
...
All of these claims for early photosynthesis are highly controversial and have engendered a great deal of spirited
discussion in the literature (Buick, 2008)
...
The accumulated evidence suggests that photosynthesis began early in Earth’s history, but was
probably not one of the earliest metabolisms and that the earliest forms of photosynthesis were anoxygenic, with oxygenic forms
arising significantly later
...
Chlorophylls are themselves the product of a long evolutionary
development, and can possibly be used to help understand the evolution of other aspects of photosynthesis
...
The early part of the pathway is identical to heme biosynthesis in almost all
steps and has clearly been recruited from that older pathway
...
The earliest version of the pathway (and that used by most modern anoxygenic photosynthetic
organisms) almost certainly was anaerobic, both not requiring and not tolerating the presence of O2
...
This has been explained in terms of gene
replacement of the genes coding for the enzymes at these steps, with the result that the overall pathway is unchanged but the
enzymes at key steps are completely different in different groups of phototrophs (Raymond and Blankenship, 2004)
...
This is an appealing idea
and probably at least partly true
...
, 2007)
...
45 bya

Primary endosymbiosis
• One ancestral cyanobacteria was 'eaten'
• Chloroplasts have a double membrane envelope
• Terrestrial plants evolved from green algae

origin of photosynthesis is to be found in the bacterial domain
...
Carotenoids, unlike chlorophylls, are also found in many othertypes
of organisms, so their evolutionary history may reflect many other functions in addition to photosynthesis (Sandman, 2009)
...
A wealth of
evidence, including structural, spectroscopic, thermodynamic, and molecular sequence analysis, clearly segregates all known RCs into
two types of complexes, called type I and type II (Blankenship, 2002)
...
The primary distinguishing feature of the two types of RCs are the early
electron acceptor cofactors, which are FeS centres in type I RCs and pheophytin/quinone complexes in type II RCs
...


○
View larger version:

• In this page
□

• In a new window
• Download as PowerPoint Slide
Figure 2
...
The colour coding is the same as for Figure 1and highlights the electron acceptor portion of the RC
...


□ Multiple primary events
□ PB and Chl b separately
□ Believed incorrect
□ Fatty acids
...
Amino acids
 Subsequently lost the ability

Electron Donors
• Determines oxygenic/anoxygenic nature
○ Water as an electron donor provides oxygen when hydrolysed
• Early photosynthesisers didn't use water
• Proteobacteria
○ Sulphide, ferrous iron, hydrogen, etc
...

• FAPs
○ Sulphide, H, etc
...
2bya
 End of Archaean period
 Oxygenic photosynthesis taking place
○ Driving force for the evolution of organisms
○ Ran out of iron, water plentiful
 In oceans

Further analysis strongly suggests that all RCs have evolved from a single common ancestor and have a similar protein and cofactor
structure
...
, 2006)
...
Figure 3 shows a schematic
evolutionary tree of RCs that is derived from this sort of analysis
...
5) and that multiple gene duplications have given rise to the heterodimeric (two related yet distinct proteins that form the
core of the RC) complexes that are found in most modern RCs
...

Schematic evolutionary tree showing the development of the different types of RC complexes in different types of photosynthetic
organisms
...
(2006)
...
Red stars indicate gene duplication events that led to heterodimeric
RCs
...


A second important issue that relates to RC evolution is the question of how both type I and II RCs came to be in cyanobacteria, while
all other photosynthetic prokaryotes have only a single RC
...
, 2007)
...
In the selective loss hypothesis, the two types of RCs both evolved in an
ancestral organism and then loss of one or the other RC gave rise to the organisms with just one RC, while the ability to oxidize water
was added later
...


 Oxygenic photosynthesis taking place
○ Driving force for the evolution of organisms
○ Ran out of iron, water plentiful
 In oceans

○

homodimer, while red indicates protein heterodimer complexes
...
Helio, Heliobacteria; GSB, green sulphur bacteria; FAP, filamentous anoxygenic phototroph
...
The various proposals that have been made to explain this fact can all be
divided into either fusion or selective loss scenarios or variants thereof (Blankenship et al
...
In the fusion hypothesis, the two
types of RCs develop separately in anoxygenic photosynthetic bacteria and are then brought together by a fusion of two organisms,
which subsequently developed the ability to oxidize water
...
Both scenarios have proponents, and it is not yet possible to choose between them
...

However, additional electron transfer processes are necessary before the process of energy storage is complete
...
These complexes oxidize quinols produced by photochemistry in type II RCs or via cyclic processes
in type I RCs and pumps protons across the membrane that in turn contribute to the proton motive force that is used to make ATP
...
, 2005)
...
The evolutionary origin of this complex is not yet clear
...
, 2008)
...
While the presence of an antenna is
universal, the structure of the antenna complexes and even the types of pigments used in them is remarkably varied in different types
of photosynthetic organisms
...
So while evolutionary relationships are clear amongsome
categories of antennas, such as the LH1 and LH2 complexes of purple bacteria and the LHCI and LHCII complexes of eukaryotic
chloroplasts, it is not possible to relate these broad categories of antennas to each other in any meaningful way
...

Previous SectionNext Section

CARBON FIXATION PATHWAYS
Most phototrophic organisms are capable of photoautotrophic metabolism, in which inorganic substrates such as water, H2S, CO2, or
HCO3 are utilized along with light energy to produce organic carbon compounds and oxidized donor species
...
By far the dominant carbon
fixation pathway is the Calvin-Benson cycle, which is found in all oxygenic photosynthetic organisms, and also in most purple bacteria
...
, 2009)
...
Similarly, the aerobic anoxygenic phototrophs, which are closely related to the purple bacteria, lack any apparent
ability to fix inorganic carbon
...
, 2007)
...
This would be consistent with the idea that the earliest phototrophs were
photoheterotrophic, using light to assimilate organic carbon, instead of being photoautotrophic
...


Previous SectionNext Section

TRANSITION TO OXYGENIC PHOTOSYNTHESIS
Perhaps the most widely discussed yet poorly understood event in the evolution of photosynthesis is the invention of the ability to
use water as an electron donor, producing O2 as a waste product and giving rise to what is now called oxygenic photosynthesis
...
Several lines of geochemical evidence indicate that free O2 began to
accumulate in the atmosphere by 2
...
In order for O2 to accumulate, it is necessary that both the biological machinery needed to produce it has
evolved, but also the reduced carbon produced must be buried by geological processes, which are controlled by geological processes
such as plate tectonics and the buildup of continents
...


○

Oxygen is produced by PSII in the oxygen evolving centre, which contains a tetranuclear manganese complex
...
Several sources have been suggested, but so far no convincing evidencehas
been found to resolve this issue (Raymond and Blankenship, 2008)
...


○ Secondary plastid has 3 membranes
 Cyanobacterial
□ Inner
□ Outer
 Chloroplast ER

Previous SectionNext Section

CONCLUSION
The process of photosynthesis originated early in Earth’s history, and has evolved to its current mechanistic diversity and phylogenetic
distribution by a complex, nonlinear process
...


From ...
org/content/154/2/434
...

○ Hormones/growth factors
 Auxins
 Ethene
 Etc
...
They
are filamentous, microscopic, absorptive organisms that reproduce both sexually and asexually
...
5 million - 6 million
• Missing entire branches of the fungal tree of life

Evolution

http://www
...
com/nature/journal/v443/n7113/full/443758a
...
curvatum's spores
 Microsporidial polar spores
 These changes link to colonisation of land by plants
□ Mycorrhizae
□ Significantly expand roots
 400m for one liverwort
□ Since 450mya
□ 95% of plants now micchorizal
□ Get carbon from plant
 Symbiotic
• Analogy 2: plants are solar panels, fungi are the national grid
• The curious case of microsporidia
○ Tiny
○ Obligate unicellular parasites
○ Infect invertebrates, fish, and sometimes humans
○ Once considered protists
 Now fungal
 Firm phylogenetic evidence
○ Why the confusion?
 Reduced genome and morphology
 Evolve very rapidly
□ Hence reduction in genome
□ More adaptive to hosts
 Lack mitochondria
□ Mitosomes
 All due to parasitic lifestyle
• Cryptomycota
○ Separate from every other fungi
○ Global freshwater habitats
○ Parasitise plankton?
○ Zoospores
○ Familiar life cycle to mycologists
○ No chitin in cell walls
○ Link between fungi and animals
 No chitin
 DNA similar to fungi

Biosphere Page 26

http://www
...
org/stable/1943156

Trilobites
27 November 2014

13:27

• Extinct class of arthropods
○ 570-250mya
• Date to early cambrian
• High degree of complexity
• Exhibit complex body plan
• Compound eyes
• Marine
• 20-70mm long
Trilobites
...
htm
Morphology
• Dorsal morphology
○ Cephalon
 Head
 Supports eyes, mouth, antennae, and limbs
○ Thorax
 Articulated segments
○ Pygidium
 Final 4-5 segments
○ Carapace most commonly preserved
• Ventral morphology
○ Exoskeleton margin
 Doublure
○ Hypostome
 Calcified mouthpart
 Can be fused with doublure
□ Counterminant
 Can be free
□ Natant
○ Sutures
 Where plates meet
 Used in classification
 Involved in moulting
• Cephalon
○ 5-7 segments
○ Glabella
 Part of axial lobe, running along back of trilobite
○ 2 cheeks
 Fixagena (fixed)
 Libragena (free)
○ Eye on palpebral lobe
 Near middle of head
• Thorax
○ 0-100 segments
○ Supports biramous legs
 Solid leg and other appendage, often gill
 3-4 pairs on cephalon (head)
 5 pairs on thorax and pygidium
 Sometimes the coxa (first segment) have large spines
□ Gnathobases
□ Involved in feeding
○ Articulation allowed enrollment
 Anti-predation
 Used to identify taxa
 4 types
□ Spherical
□ Double
□ Discoidal
□ Incomplete
 Genal and pygidial spines deterred predation
○ Segments allowed movement
○ Processes (anterior flange) fit into the sockets (posterior flange) on the adjoining
segment
Internal Anatomy
• Poorly understood
• Largely inferred from extant crustaceans
• Through-gut
○ Stomach in cephalon
○ Gastric caecae
 Pockets
 Increase SA
• Dorsal blood vessel
○ Heart
• Collection of ganglia in cephalon
○ Brain
Biosphere Page 27

Ecology and Feeding
• Typically benthic
○ Sea bed
• Predatory/scavenger species
○ Large gnathobases at top of exopod
○ Counterminant hypostomes
 Mouthparts fused with doublure (exoskeletal margin)
 Food masticated in longitudinal medial groove
• Particle feeders
○ Natant hypostomes (free of doublure)
 Varied with diet
○ Dominated cambrian and lower Ordovician
○ Fed upon organic matter
• Pelagic planktivores
○ Streamlined
○ Large eyes
○ Possible plankton diet
○ Limited enrollment
 Spikes
• Filter feeders
○ Enlarged cephalon
○ Perforated
 Gills/legs used to generate current into cephalic chamber
 Edible particles ingested
○ Hypothetical
 Only cephala found
Ontogeny
• Little known about reproductive biology
• Potential brooding in anterior brood pouch
○ Strange bulge on female(?) fossils
• 3 developmental stages
○ Protaspid
 Larval form
 No articulation
 Possibly planktonic
□ Dispersal
○ Meraspid
 2 or more segments
 More segments at each moult
 Ends once adult number of segments reached
○ Holaspid
 Adult number of segments
 Grows at each moult
□ Segment number the same
 May have reached terminal moult
□ No more growth
 Sexual maturity reached
Evolutionary History
• First appeared in mid-Cambrian
○ Earliest fossils
○ Probably around earlier
• Peaked late Cambrian/early Ordovician
• Lasted 2
...
5mya

Cenozoic
65
...
Walruslike reptiles, placodonts, appeared in the
shallow seas"
□ Icthyosaurs
□ Mammals
□ Frogs
○ Marine recovery
○ Living relatives
 Norfolk island pine
□ Similar to triassic conifers
 Tuatara
□ Only 2 species remain
□ Resembles triassic sphenodontians
 Large, diverse group
• End-triassic mass extinction
○ Extinguished 76% of species
○ Marine invertebrates
 Conodonts disappeared
□ Small fossil record
○ Terrestrial vertebrates
 Large amphibians disappear
 Large, non-dinosaurian reptiles disappeared
□ Except for crocodilians
□ Crurotarsans
□ Mammal-like reptiles etc
...
7-416mya
• Northern continents
• Ocean basins narrow
• Ice melted
○ Seas rose
• Shallow seas expanded
• Life
○ Plants
 Invaded freshwater and land
○ Invertebrates
 Invaded land
 Extensive reefs
○ Vertebrates
 Jawless fish radiate
□ Invertebrates still top predators
 Jawed fish
□ placoderms
○ Living relatives
 Brittlestars
Devonian Period
• Warm, dry climate
• Northern continents divide
• Tropics
○ Dry land
 Arid and humid
○ Warm shallow seas
• Seas
○ Geochemistry changes
○ Periods of hypoxia
• Life
○ Plants
 More land plants
 Evolve adaptation to keep water
 Roots, seeds, transport systems, woody
tissues
□ Trees
 Cause creation of soils
○ Invertebrates
 Arthropods colonise land
 Massive reefs
○ Vertebrates
 Freshwater fish
 Placoderms
 Sarcopterygians
 Sharks
 Aquatic tetrapods
• Mass extinctions
○ Multiple events
○ Over a large period
○ 22% marine animals
○ Black shale
 Lack of oxygen in seas
○ Glaciation
 Plants removing CO2
○ Weathering
 Plants
 Nutrient input to seas leading to
stagnation
 Carbon sinks
○ Kellwasser Event
 Warm, shallow water
□ Marine invertebrates
 Eliminated reef builders
□ Brachiopods, ammonites
 Survivors
□ Evolved smaller eyes and larger
respiratory surfaces
□ Poor visibility and low O2
○ Hangenberg Event
 Sea and freshwater
 Ammonites, trilobites, placoderms,
sarcopterygians, tetrapods
 Living relative

Biosphere Page 29

Jurassic Period
• Disintegration of Pangaea
○ Ocean widened
 Shallow water environments widespread
• Climate
○ Globally warm and humid
○ Cooled in mid-Jurassic
• Life
○ Plants
 Ferns, conifers, cycads, gingkos
○ Marine invertebrates
 Radiation of bivalves, corals, echinoderms, bryozoans,
corals, lobsters
 Growth of large sponge reefs
 Adaptation of burrowing strategies
□ More successful predators
○ Vertebrates
 Radiation of dinosaurs
□ Theropods, sauropods, Ornithischians
 Massive and majestic
 Radiation of crocodylomorphs
□ Only surviving crurotarsans
 Radiation of large marine reptiles
 Evolution of birds
○ Living relatives
 Selaginella
□ Moss-like
□ Little change since Jurassic
 Horsetails
□ Widespread
□ Larger in Jurassic
 Gingko
□ Only one remaining species
□ Widespread and diverse in Jurassic
 Giant dragonfly
□ Petalura gigantea
□ Similar to Jurassic libellulium

Cretaceous
• Pangaea continued to disintegrate
• High CO2 levels
○ Hot climate
○ High sea levels
 Huge, shallow seas
• Life
○ Plants
 Evolution of flowering plants
□ Diversified through the cretaceous
○ Invertebrates
 Evolution of pollinators
 Marine invertebrates
□ Radiation of bivalves, ammonites, snails
○ Vertebrates
 Radiation of dinosaurs, birds, sharks, bony fish
○ Living relatives
 Plants
□ Magnolia
□ Water ferns
□ Quillwort
□ Dipteris
□ Monkey puzzle
□ Welwitschia mirabilis
□ Redwoods
 Thorny oyster
 Slender roughy
 Gar pikes
 Duck billed platypus

respiratory surfaces
□ Poor visibility and low O2
○ Hangenberg Event
 Sea and freshwater
 Ammonites, trilobites, placoderms,
sarcopterygians, tetrapods
 Living relative
□ Lycophytes
 Mosses
□ Glass sponges
 Silica based
Carboniferous Period
• 359-299mya
• Pangaea
• Climatic extremes
○ Tropical forests
○ Ice ages
• High O2
○ Loss of development of life
• Life
○ Plants
 Greater diversity
□ Trees, herbs, climbers
 Complex ecosystems
○ Invertebrates
 Radiation of terrestrial arthropods
 Marine ecosystems
□ Reef-formers
○ Vertebrates
 Radiation of jawed fish
 Tetrapods
□ Terrestrial
□ Amniotic egg
 Full terrestrial
tetrapods/reptiles
Permian Period
• End of proterozoic
• Glaciation
• Drier
○ Swamps lost
○ Deserts
 Reptile radiation
• Upland forests
○ Plants continued to diversify
• Sea level
○ Dropped
○ Continental shelves exposed
• Life
○ Plants
 Extinction of ancient plant groups
 Radiation of conifers and cycads
□ Drier climates
○ Invertebrates
 Algal reefs
□ Brachiopods and bryozoans
 Disappeared as seas lowered
○ Vertebrates
 Synapsid reptiles radiated
□ Mammalian ancestors
 Ray-finned fish radiated
• End-Permian Mass Extinction
○ Greatest extinction
○ Wiped out
 90% of marine species
□ Marine invertebrates worst
effected
 Survivors:
◊ Small
◊ Mobile
◊ Active circulation
◊ Elaborate gas exchange
◊ calcification
 70% of terrestrial vertebrates
□ 2/3 of families extinguished
 Many sauropsid
 Many therapsid
◊ Group including
mammals
□ Most surviving families lost the
majority of their species
□ Survivors:
 Lystrosaurus
◊ Herbivorous
dicynodont therapsid
(two teeth)
 Cynodont and archosaurs
◊ Ancestors of bird and
mammals
○ Only known insect mass extinction
 Terrestrial invertebrates
□ Most insect orders extinguished
 Larges insects ever
□ Survivors
 More similar to modern
groups
○ Terrestrial plants
 Few extinctions
□ Major ecosystem response
 Cyclical decline and
expansion of gymnosperm
forests
◊ Severe ecosystem
stress
○ May have occurred in up to 3 pulses
 Over several million years
○ 10 million year recovery
○ Causes
 Impact event
□ No conclusive evidence
 2 flood basalt events
□ Emeishan and siberian traps
□ Massive volcanic eruptions
 Blocked sunlight, acid rain,
warming
 Gasification of methane hydrates
□ Accumulate beneath sea-floor
□ Triggered to release methane by
volcanism
□ Massive global warming
 Anoxic event
□ Oxygen depletion of sea water
 CO2 release by volcanic
eruption
□ Release of hydrogen sulphide by
anaerobic bacteria
 Kills terrestrial plants

Biosphere Page 30

□ Monkey puzzle
□ Welwitschia mirabilis
□ Redwoods
 Thorny oyster
 Slender roughy
 Gar pikes
 Duck billed platypus
□ Similar to cretaceous Teinolophus
• Cretaceous/Tertiary (K/T) extinction
○ Plants and marine primary producers
 Severely reduced in numbers
 Some extinctions
○ Marine invertebrates
 Almost total extinction of colonial corals
□ Depend on algal symbiosis
 Extinction of many cephalopod groups
□ e
...
ammonoids
○ Vertebrates
 Extinction of dinosaurs, archaic birds, pterosaurs,
large marine reptiles
○ Impact event (almost certainly
 Layer of iridium rocks
□ Rare on Earth
□ Common in asteroids
 Chicxulub crater
□ In Central America
□ Most likely site of impacts
 Effects
□ Dust cloud
 More than one year of darkness
□ Sulphuric acid aerosols
 20% sunlight blocked for more than a
decade
◊ Killed photosynthesisers
□ Infrared pulse and global firestorm
 Killed exposed organisms
 Reduced oxygen and increased carbon
dioxide
○ Other causes
 Volcanism
 Drop on sea level
□ Reduction in shallow seas
□ Expanded freshwater



---

Title: Biosphere
Description: Notes from the first year 10 credit IBERS Biosphere module taught at Aberystwyth University by Helen Marshall, Ian Scullion, Arwyn Edwards, and Joe Ironside. This module covers atmosphere, pedosphere, hydrosphere, cryosphere, biogeochemical cycles, frozen lands, prokaryote and eukaryote evolution, evolution of photosynthesis, succession onto the land, trilobites, funal evolution, and mass extinctions

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