How has the Earth changed Flashcards
1
Q
Oxygenation event
A
2.8billion yrs ago (began slightly 3.8Ga)
cyanobacteria and photoferrotropes began to produce O2
O2 reacted with Fe in sea to produce FeO which settled to produce banded iron formations
2.3billion yrs ago
o2 enter atmosphere
changed atmosphere
reacted with methane
Photosynthesizers removed CO2 from atmosphere
temp drop
mass glaciation (Huronia)
mass extinction
poisoned most anaerobic organisms
produce ozone layer
2
Q
what is a snowball earth
A
when Icesheets surround earth - only happened 2-3x
3
Q
How do snowball earths occur
A
CO2 removed from atmosphere due to eruptions of basalt + produces SO2,
Particles block sun –> solar diming
leads to cooling
in the long time to greenhouse gases heat and undo ice age
(increased photosynthesis also decreases CO2)
4
Q
CO2 levels throughout geological time
A
peaked in the Cambrian- 7000ppm
then decreased slowly till about 250million yrs ago when it rose again till 150ma
then decreased till modern day with us now having some of the lowest levels ever
5
Q
implications of CO2 on climate and sea levels
A
Recent : high CO2 levels = hot climate and high sea levels (as less H2O stored as ice)
positive feedback loop
Over time however temperature hasn’t necessary followed the same trend as CO2 - might not be main effector of climate
6
Q
What was earth’s early atmosphere + why?
A
originally H + He when solar system formed –> then light gases escaped
then became CO2 dominated due to volc activity (similar to venus) –> similar to Hawaiian volc emissions
Some H2O vapour, N, NH3 and CH4
little O2
H20 condensed to form oceans about 4Ga –> mostly CO2 left in atmosphere
7
Q
What is a greenhouse earth + when did it last occur?
A
when the global temperature is hotter than average + no continental glaciers
warm periods
last in early tertiary 33.9Ma
8
Q
What causes greenhouse earth?
A
can be:
increased solar radiation reaching earth
or changes in gas concs in atmosphere
or volcanic eruptions—> greenhouse gases over time raise temp
breakup of continents associated with greenhouse conditions
9
Q
What is an icehouse earth? + when was the last?
A
Colder than usual- lower average global temps
icecaps and glaciers on continents- large continental icesheets at poles
currently in one
10
Q
What causes an icehouse earth?
A
caused by increased reflection of solar radiation back to space (albedo effect)
+ volc events - release sulphate aerosols reflect back solar radiation
cooling
often linked to aggregation of continents
e.g. Pinatubo eruption in 1991 decreased temp of northern hemisphere 0.6 degrees
11
Q
Eustatic definition
A
Sea level changes due to changes in vol of ocean basins or vol of H2O in them
these changes can be seen worldwide
also thermal expansion of H2O as seen at MOR/ ice melting
12
Q
Isostatic definition
A
Sea level changes due to uplift or subsidence of cont crust.
often sinks when loaded with ice/ sed and rises when load removed
only seen in affected region
only appears to change doesn’t actually
e.g. Scotland undergoing isostatic rebound –> beaches look raised
13
Q
What is the phanerozoic
A
Most recent Eon of time (current)
when life became complex
Cambrian to Quaternary
~500Ma - 0Ma
14
Q
what happened to sea levels over the phanerozoic
A
as the temperature increased so did sea level
rose from Cambrian to Ordovician peaking mid Ordovician at the highest it has even been
then decreased till the breakup of Pangea in the early Permian
then began to rise again till it peaks mid cretaceous - high
then drops again
15
Q
How do rocks evidence climate change
A
diff rocks are more prevalent + dominant in different climates e.g. some rocks form from different weathering
some only form in certain climates
16
Q
what rocks are used to identify climate
A
Coal
Desert sandstone
Evapourites
Tillites
Reef limestone
all of these rock types are found in UK
17
Q
what does Coal tell us about past climate
A
Warm and wet
mostly from Carboniferous in UK
Must be highly productive ecosystem = peat
rapid plant growth + high rainfall and temp e.g. rainforest
18
Q
what does Desert sandstone tell us about past climate
A
Hot, arrid and dry
sand exposed to air -> oxidised -> red
fine grained + V well sorted + well rounded
Mostly quartz
transported by wind -> dunes
Occurs 20-30 degrees north or/and south
19
Q
what does Evapourites tell us about past climate
A
desert + quick change from wet to dry
form where low rainfall and high evap e.g. hot desert
found at latitudes 20-30 degrees north or/and south
20
Q
what does Tillites tell us about past climate
A
Glacial deposits –> cold enviro
ancient boulder clay -> commonly formed at high latitudes
more than 60 degrees north/south of equator
some in low latitudes
21
Q
what does Reef limestone tell us about past climate
A
warm and shallow
mainly built of colonial corals
restricted to latitudes < 30 degrees north/south of equator
likely at this latitude
22
Q
what is palaeontology
A
the branch concerned with fossilised organisms
23
Q
How does paleontology evidence climate change
A
diff organisms based in diff atmospheric conditions
certain species associates with certain climates e.g. corals
based on modern day animals tell what similar past species preferred for climate
24
Q
corals as evidence of past climate
A
modern - live in narrow range of temp and depth -> 30degrees N or S of equator - allowing for symbiotic relationship with algae
Palaeozoic tabulate corals have similar O18 : O13 as modern corals = require same tropical conditions
25
Plants as evidence of past climate
excellent indicators e.g. tree rings, leaf size and shape
lack of tree rings in carboniferous suggest non seasonal equatorial climate = same as modern day
also grew to 40m+ = hot humid equatorial climate and latitude allowing biomass to accum
26
isotope
atom of an element with the same no of protons but different no of neutrons
same chem props (same no of outer shell electrons) diff physical props
27
isotopes of O as past enviro indicators
O16-99.76% O17-0.04% O18- 0.20%
normal= O16 evaps, falls as precipitate -> returns to ocean
O16 evaps as lower mass so requires less e to evap --> more easily
cold period= glaciers -> O16 trapped in ice -> amount of O18 increases in comparison to O16 in ocean
^ O18:O16 = colder climate
28
isotopes of C as past enviro indicators
C12- 98.9% C13-1.1%
plants prefer C12 + take up
Warm= more plants -> more C12 taken up + stored, ratio of C13:C12 in ocean increases e.g. 5:95 instead ( if too warm kills plants and opp happens)
Cold= No plants, No C12 stored so ratio of C12 in ocean increases, C13:C12 decreases
ratio preserved in sed then becomes rock
29
evidence for Northward drift of the British isles in rocks
tillites - Precambrian in west scot = glaciation
colonial corals- in silurian wenlock limestone + jurassic - shallow tropical sea
red sandstone +evapourites - permian + triassic = 30 degrees N of equator
reef limestone- lower carboniferous in Pennines = tropical seas
coal - scot to kent carboniferous = equitorial rainforest delta
Chalk- cretaceous = temperate as moved north into cooler climate - rep modern climate
30
what is an eon + current
largest unit of geological time
Phanerozoic
31
The 4 Eons
Hadean, Archean, Proterozoic and phanerozoic
32
What is an era + current
smaller than eons larger than periods
Cenozoic
33
The 4 eras
Precambrian, Palaeozoic, Mesozoic and Cenozoic
34
What is a period + current
smaller than eras larger than epochs
Quaternary
35
The 11 periods
Cambrian, Silurian, Ordovician, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, tertiary and quaternary
36
What is a epoch + current
smallest unit of geological time
holocene
37
Arguments for the Anthropocene epoch
The human impact on Earth (climate and enviro)
Current mass extinction
38
Arguments against the Anthropocene epoch
only very short time period
geological events occur over long period of time not abruptly
recency bias
not yet accepted by international commission on stratigraphy
39
5 major extinction events oldest to youngest
Ordovician- Silurian (443ma) cooling
27% of all families
57% of all genera
e.g. bivalves, brachio, trilobites
late Devonian- (372ma) cooling/volc
19% of families
50% genera
e.g.brachio, trilobites
Permo-triassic- (252ma) volc? lava + gases
57% families
83% genera
e.g.bracio, trilobites and trees
Triassic-jurassic- (201ma) volc eruptions
23% families
48% genera
e.g. most early dinos
cretaceous tertiary- (66ma) asteroid
17% families
50% genera
e.g. dinos, ammonites, bivalves
40
Evidence for current mass extinction- driven by human activity
species extinction rate 1000-10000x higher than natural
amphibians greatest rate 25000-40000x background rate
excluding bacteria there are 8.7 million species so at a rate of 50000 a yr we will have none in 174yrs
more reasonable to lose 75% of species in next few centuries
41
What is a marker horizon
stratigraphic units of same age and distinct composition and appearance
allow to determine age / time period formed in
easily distinguished
42
What is GSSP
Often referred to as golden spike
Golden standard stratotype - sections + points
locations where strata show evidence on worldwide scale --> set as boundary for time period
43
Examples of GSSP
iridium from asteroid - Cretaceous tertiary
plutonium-239 (half life = 24000yrs) from nuclear testing e.g. bikini atoll
agriculture - adding N + P as fertiliser
plastic
soot from industrial rev
44
What is evolution
Process by which the inherited characteristics of a pop are passed on from parents to their offspring
45
What theories did Charles Darwin develop
Natural selection - strongest survive and pass on genes
46
phyletic gradualism def
model of evolution which states that most speciation is slow, uniform and gradual
47
adaptive radiation def
a process when organisms diversify rapidly into many dif forms
48
species definition + geology specific one
an organism that can breed with similar organism to produce fertile offspring
you cant apply this to geology instead we use morphology - as most extinct
49
phyletic gradualism description
model of evolution which states that most speciation is slow, uniform and gradual
process of gradual evolution over time -> involve the creation of new genes/ characteristics due to crossbreeding and mutation
smooth and continuous
50
evidence for phyletic gradualism
lineage of whales
gradually evolved from 4 legged mammals to aquatic mammals over millions of years
51
Genetic drift description (same as bio)
random sampling of parental genetic material in offspring leads to the elimination of some genes/characteristics #
genes passed on not necessarily the better ones
survivors are random - likely due to catastrophic event in small pop or few selection pressures
52
Evidence for genetic drift
survival is random e.g. brown rabbits may all survive a fire but all white rabbits die
nothing to do with colour merely random
53
adaptive radiation/Fossil ranges description
geo time is marked by mass extinctions followed by adaptive radiation
seen by changing numbers of groups of different fossils throughout geo time
a process when organisms diversify rapidly into many dif forms from ancestral species
54
evidence for adaptive radiation/fossil ranges
Darwin's finches
55
punctuated equilibrium description
over very long period of time there is little change in as population as it expends
stasis
at limit of enviro the organism is forced to change, new species develops and takes over
instead of 1 species gradually changing it just splits in 2 distinct species
56
punctuated equilibrium evidenece
Trilobites
57
gene flow description
exchange of genes between populations
e.g. by migration in a animals or pollination in plants
carries gene not prev found within that population leading to genetic variation
58
gene flow evidence
bees bringing pollen from 1 pop of flower to another allows interbreeding and reproduction
59
5 Different theories of evolution
Phyletic gradualism
Genetic drift
Fossil ranges/ adaptive radiation
punctuated equilibrium
Gene flow
60
how has the discovery of DNA changed evolutionary bio
Watson and crick
produced double helix DNA model
(Xray analysed Rosalind Franklins data)
we could now see minor changes in genes (often mutations) where passed onto offspring as they increased survival + repo chances
replaced earlier genes in gene pool
allow the establishement of interrelationships
not in Geo as fossil
61
Trilobites background information
most successful and abundant animal in its time
existed between 521-252ma
survived 3 mass extinctions
arthropods
many different families
62
Key features of trilobite morphology
spilt into 3 segments - the cephalon (head), the Thorax (body) and the pygidium (tail)
3 lobes - left right and middle
antenna- detect enviro
appendages- walking and swimming
glabella- central region of cephalon
compound eye- sensory
free cheek-breaks away during ecdlysis
facial suture-line of weakness were exoskeleton first breaks
fixed cheek- remains attached
genal spines- attached to genal angle on cephalon (only in some species)
pleuron- segment adjacent to the axis, support gills
axis- central lobe
Made of calcite/chitin
63
General adaptations
of trilobite
could curl up into balls (many segments) - deal with predation
spiney/spikey - deal with the evolution of jaws
compound eyes- calcite crystals (one of the first eyes)
64
Benthonic trilobites e.g. calymene
live on sea bed- Little streamlining
complex compound eyes - sensitive to movement + depth - active hunters
many pleura - rolling for protection
gills- respiration = active metabolism = active hunter
bottom dweller - crawl
genal spines - prevent sinking into mud as increase SA ( OCR FOCUS ON GENAL SPINES FOR BURROWING AND BENTHONIC)
65
Pelagic trilobites e.g. Opipeuter
live in the H2O column
streamlined - smoot, elongated and flat for swimming
very large compound eyes (see back, forward, up and down - as they live where light reaches - used for hunting/ escaping predators
more articulated parts
small
separated pleura and inflated glabella- buoyant
strong muscles - good swimmer
66
Burrowing trilobite e.g. Trinucleas and Asaphus
asaphus- 2 compound eyes on sticks on top of head - body buried and eyes stick out
trinucleus - had no eyes as too deep
large genal spines
lots of pores on surface- sensory or filter feeders
spines- increase SA - prevent sinking
epifaunal or infauna
shovel shaped cephalon- dug shallow burrows for protection/ feeding on organic rich sand
67
features specific to cnidarians
uncentralised nervous system
lots show radial symmetry
body = mesoglea - non-living jelly like substance
can repo sexually and asexually
cnidoblast- specialised cell with ejectable flagella
68
features and behaviour of modern coral
coral polyp (soft part) - living part
has tentacles ,mouth ,cilia ,nemoblasts(stinging cells)
polyp secretes CaCO3 -> builds reef structure (polyp sits in depression)
solitary or colonial - most colonial
single coral polyp = corallite ( a cup like calcerous skeleton)
69
what enviro is required for reef building
warm shallow sea
high light availability- low turbidity so clear
constant salinity
use comparison to current corals when looking at fossil to assume their enviros
(some rare corals are in cold deep water)
70
Symbiotic relationship of corals and algae
coral polyps incorporate photosynthesising algae (zooxanthellae)
produce 95% of coral polyps energy
in exchange zooxanthellae get protection
71
How do corals gain their other nutrients
by preying on small marine organisms-> using nematocysts/ tentacles/cilia to kill prey-> move to mouth
72
which parts of corals are preserved
CaCO3 - hard parts
soft coral polyp decays or is scavenged
73
Rugose corals
Extinct Ordo-permian
solitary but can be colonial
bilateral symmetry due fossula
No mural pores
tabulae are always present
corralite = large + many
columella are always present
dissepiments sometimes present
major septa at 6 pints and 4 minor
e.g. Lithostrotian sp.
74
Tabulate coral
Extinct - cambrian-permian
Always colonial
radial symmetry
Mural pores may be present - ONLY HERE
lots of clearly defined tabulae
corralite = may be small
columella - absent
dissepiments absent + sometimes reduced
septa- sometimes present but absent or reduced
Hexagonal
e.g. Halysites sp
75
Scleractinian coral
Extant - triassic-today
colonial or solitary
radial symmetry
No mural pores
tabulae always present
many small corralite
dissepiments always present
major septa at 6 points radially - hexagonal
major reef building now
e.g. Thesomillia sp
76
Tabulate def
horizontal plate dividing corallite skeleton
77
dissepiments def
curved plates connected to septa + tabulae
78
columella def
axial rod which supports the septa running up centre of coral
79
septa def
vertical plates radially diving the corallite skeleton
80
Mural pores def
connections between adjacent corallites perhaps for communication
81
Features of a brachiopod
shell made up of 2 valves
2 or more muscles - (only scars preserved) - open + closed at rest
adductor-closed , diductor-opens (if 3 then 3rd = pedicle stork- emerges from pedicle forearm)
bilateral symmetry (along middle of shells)
umbo-point of first growth
commissure - where brachial (bottom valve) and pedicle (top valve) meet
growth lines- rep new layers of shell
deltoidal plates- cover triangular area below forearm
common in paleozoic + rely in current to feed
82
How have brachiopods adapted for turbulent water
large pedicle opening (foramen)- support large pedicle for secure attachment to substrate
strong ribbed valves - strengthen shell against wave action
folded/zigzag commissure- reduced amount/size of sed entering when valves open
thick + heavy shells- extra stability on sub + prevent rolling in current
83
How have brachiopods adapted to calm waters with soft substrate
may have median fold + sulcus - sep current of H2O entering and leaving -> prevent fresh + waste mixing
valves flat -> large SA dont sink
may have extension of valves forming wings -> large SA dont sink
smooth/weakly ribbed valves - no need to be robust
no pedicle opening- dont need pedicle for attachment
one margin of shell turned upwards - ensure "mouth" remains out of H2O for feeding
84
How have brachiopods adapted for hard substrates
elongated ventral valve - cemented to sub at base - for attachment in high energy enivro
spines from ventral valve - stabilise by extending into sub prevent overturning by current
small brachial valve - lid to open for feeding + respiration
85
Brachiopods and reef building
common in Permian reefs which are seen in Texas, south east asia and sicilly
preserved in life assemblages
brachiopods don't secrete anything to build the reefs this comes from corals, sponges and algae ect
86
Features of bivavles
bilateral sym on hinge line
1 set of muscle scars - open at rest use adductor muscles to close
also have an umbo + hinge teeth
have 2 valves - left and right
concentric ridges
pallial sinus- where siphons were
commissure
87
similarities between bivavles and brachiopods
2 calcerous valves
umbos
growth lines
ribs
filter feeders
both have hinge line
both have muscle scars
both have commissure
both have bilateral sym
88
Differences between bivalves and brachiopods
shell shape-
brachio- 2 diff sized valves (pedicle=larger)
bi- identical sizes
shell symmetry-
brachio- bilateral about plane from umbo to anterior margin
bi- bilateral on hinge line
opening and closing muscles-
brachio- adductor (close) and diductor (open) 2 sets of muscles
bi- only adductor (open at rest)
foot-
brachio-none
bi- found at posterior for movement + digging
pedicel-
brachio- attached to rocks
bi- none
pallial lines + sinus-
brachio- none
bi- clearly seen around margins of shell
feeding-
brachio- lophophore
bi- Ctenidia?
89
What are amphibians?
a creature with 2 lifestyles 1 in H2O 1 on land - OCR
aquatic gill-breathing laval stage -> terrestrial lung-breathing stage
90
What did amphibians evolve from?
Lobe finned fish
fish -> lobe finned fish -> amphibians
late Devonian -> early carboniferous
91
Lobe finned fish morphology
fleshy fins - contained bones similar to hands allowed for more stability and support + to move through reeds
couldn't put weight on them so not feet
ability to breath out of H2O -> due to modified swim bladder -> access O2 from it (primitive lung) -> move from 1 water source to another
swim bladder was og used for buoyancy
= no strengthen girdle -> connect limb bones to rest of skeleton - area of weakness
92
How do we know about the morphology of lobe finned fish
fossils in Devonian strata
show even earlier skeleton structure
+ still alive today e.g. coelacanths
93
similarities between lobe finned fish and early amphibians
4 fins of each are skeletally similar
limbs in same position
lacked claws/nails
skull morphology, jaw bone and teeth alike
amphibians skull became increasingly smaller -> temporal and opecular bone became smaller and jaw fused
both had complex teeth
early amphibians still had tail fin -> spent a lot of time in H20 -> movement + body like lobe finned fish
early amphibians had traces of small bony scales
94
adaptions that allowed amphibians to become terrestrial
skeletal gridle- connect limb bones to skeleton, for better movement on land
more robust skeleton- strengthened vertebral column + rib bones - extra support
eyelids- keep eyes be moist
double circulatory system + three chamber heart- pump mixed blood -> more efficient gas exchange - provide more active cells with O2 + remove waste more efficiently
tongue- catch prey + sensory
ears- detect sound waves through air -> listen for predator + prey
95
what is the first marine animal to become terrestrial called
Tiktaalik
96
importance of amniotic egg for dinosaurs
fluid filled sack -
didn't need H2O for reproduction
97
Key features of dino egg
Hard outer shell- protection
pores - gas exchange for respiration
yolk-food
albumin-supplied H2O and nutrients (dont need larval stage)
98
what were archosaurs?
Reptiles not dinos e.g. crocodiles
dinosaurs evolved from them after the permo-triassic mass extinction
99
FLISS
Forward
LIzard
Saurischian
S shaped neck
100
BOBBA
COMPLETE
Backward
Ornithischian
Bird
Beak
Armour
101
Saurischian Key information
Pubis forward - like reptiles
long S shaped flexible necks- rapid + precise moves
3 digits in hand - assym
1st like a thumb- allowed grasping
2nd is longest
e.g. Diplodocus - sauropod ( on 4 legs+ herbivore)
Velociraptor + T Rex - Therapod (on 2 legs + carnivore)
102
Ornithischian Key features
Pubis backward - like birds
front teeth small/absent - replaced by horny beak (got broader as evolved - ' duck billed dino')
Many armoured + bony plates -> defence or heat exchangers - Fossilised plates have tiny grooves - may have housed blood vessels - give heat off
e.g. stegosaurus
iguanodon
103
What are therapods
Branch of saurischian dinos
bipedal + carnivore
104
morphology of coelurosaurs
includes - Compsognathus + archeopteryx and Birds (shows similarities)
hollow thin walled bones- less dense
S shaped neck
elongated arms + forelimbs + clawed hands
hinged ankles (decreased rotation of ankle)
large orbital - eye socket
Pubis shifted forward (in archeopteryx + anything prior) to backward (only in birds)
105
What is Compsognathus
therapod dinosaur in the coelurosaur taxon
106
Morphology of Compsognathus
reptile skull + brain
S shaped curve
long tail
forward pubis
sharp teeth + snout - reptilian
short forelimbs
clawed 3 digit hands
reversed first toe
No furcular
gastralia- belly ribs
sternum not bony
107
Morphology of archeopteryx
same as Compsognathus-
S shaped curve
long tail
forward pubis
sharp teeth - reptilian
Hollow bones
3 clawed hands
reversal of first toe
different to Compsognathus-
Have a furcular
Long forelimbs + wing like properties + feathers
Unsure-
Metatarsals not fused
legs directly under body
108
Morphology of modern birds
Same as Compsognathus + arch-
reversed first toe
same as just arch-
furcular
different-
fused metatarsals
no teeth
large breast bone
no tail- short pygostyle
pubis backward
109
Evolution of feathers
developed as elongation of scales - unsure as scales = flat but quill of feather = tabular
may have evolved separately as diff proteins (keratin)
earliest found late Jurassic- protofeathers (simple downing feathers) - for insulation (fluffy)
some dinos grew long feathers
appeared 100 ma before flight
possibly had sexual dimorphism- males and females look different -> plumage and colour for display like birds
110
What is a mass extinction
when more than 75% (some say 50%) of species on Earth become extinct in a short period of time (geologically)
111
Ordovician Silurian mass extinction
Reasons:
cooing (Gondwanaland at south pole) -> icesheets( changed ocean chem+ feedback effect) -
climate cooled by albedo effect -> heat and light reflected so temp decreased further -> more snowfall -> more albedo so temp decrease -> repeat
lead to snowball earth
Water trapped in ice sheets so sea level dropped - destroyed cont shelf habitat ( already restricted due to Gondwanaland being at south pole) -> killed many shelf dwellers e.g. brachiopods + bivalve + corals
also effected planktonic and nektonic e.g. trilobite
case study- malformed plankton (chitinozoas) likely caused by high heavy metals conc and anoxic conditions
112
Permo-triassic mass extinction
Main Reasons-
1) Major volcanic activity- Siberian traps erupted over mantle plumbs for 1-2ma
- toxic gases+ lava flows+ pyroclastic flows
-ash -> block sun-> temp drop -> global glaciation
- after initial cooling -> emission of greenhouse gases e.g. CO2 + SO2 -> temp increased 1000s to 1,000,000s yrs
-acid rain
2) super continent + glaciation-
-Pangea formed --> super continent
-> fewer cont shelves -> lack shallow marine habitat (death of shallow marine organism- brahio, trilobite and rugose/tabulate)
-single continent = rapid flux in climate + unstable weather
-parts of pangea over N+S poles (evidence in aussie) -> mass glaciation -> sea level drop -> reduce shallow shelf enviro further
smaller reasons-
1) methane hydrates- soild methane in sed -> global temp increases -> triggers methane hydrates on sea floor to become mobile -> greenhouse gases (temp increase)
2) possible impact event
- flimsy evidence e.g. shocked quartz in aussie
-any impact crates on sea floor would be destroyed (oldest 200ma)
-technically large imoact may have caused Siberian traps - little evidence
113
Cretaceous-tertiary mass extinction
reasons-
-asteroid/meteorite impact
evidence: iridium conc in clays at boundary
shocked quartz at boundary
presence of tektites-> found near impact craters -> V low water content (not made on earth or rock melted v quickly on impact)
sed evidence of huge tsunami in Texas
large crater in Yucatan peninsula in Mexico(shown by gravity variation)
Major volc activity -
Deccan traps (india)- enormous series of eruptions over 30000yrs
same impact as Siberian traps- toxic gases, COOLED then heated (cooling more sig)
114
Why is the fossil record incomplete
bias towards hard parts
soft parts- consumed by predators, broken down by bacteria and high e enviroment
115
What are lagerstatten deposits
lots of fossils exceptionally preserved
means storage place in German
116
What general conditions are necessary for lagerstatten deposits
anaerobic - no bacteria so no decay
rapid rate of burial
fine soft sediment
low energy environment
presence of hard parts
short transport distance
117
why are lagerstatten deposits important
see fossils never preserved elsewhere e.g. soft body
observe/study features of hard bodied organisms not usually preserved e.g. feathers of dino
very fine detail preserved
internal structures preserved in some
118
Konzentrat-lagerstatten
concentration
find many organisms in 1 bed e.g. disarticulated bone bed + organic hard parts
also include high concs of fossils on reefs e.g. bivalves and oyster bed
119
Konservat-lagerstatten
Conservation
deposits known for exceptional preservation, crucial for proving evidence for history of life on earth
120
Important lagerstatten deposits
Burgess shale- Canada
Solnhofener plattenkalk- Germany
Santana formation- Brazil
Chengjiang formation- China
121
What was the Cambrian explosion
Massive surge in complex life during the Cambrian
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possible reasons for the Cambrian explosion
increased O2- previously it was too low for complex organisms to develop
increased mineral availability-for shells
development of vision
predator/prey relationships- drives evolution
May have been a mass extinction and this was the recovery
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How did preservation occur at the Burgess shale
+ evidence
initially they believed: turbidite current - anoxic basin ( as no decay)
More recent belief:
lived in deep H2O basin (algae reef + carbonate platform) - small turbidity flows covered organisms on ocean floor some dead + partly decayed some alive
reasons for new belief:
1) most organisms were buried in their habitat - only minor disturbance
2)benthonic orgs preserved in life pos e.g. brachiopods
3)most decay was prior to burial - resulting in disarticulation
4)variable amounts of disarticulation - indicate transport
5)early mineralisation of body tissues occurred soon after burial (during early diagenesis)
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Examples of preservation in Burgess shale
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Opabinia-large snout
paddle like projections at posterior
(unknown affinity)
aysheaia-velvet worm
limbed, soft bodied, segmented, spines on legs
marella-lace crab
head sheild with 4 curved spines
feather filamnets on limbs-respiration
hallucigenia- poorly defined head
spines on back - don't know if it is upside down or right way up
(unknow affinity)
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Unknown affinity def
dont know what they evolved into
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Describe the evolution of hard parts in marine animals
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Ages of the lagerstatten deposits
Chengjiang - 515Ma(early cambrian)
burgess shale-508ma (mid cambrian)
Solnhofen limestone- 155Ma (jurassic)
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How did preservation occur at the Chengjiang formation
+ evidence
turbidity flow - low O2, no scavengers and fine sediments
little transport so little disarticulation
relatively shallow marine shelf environment- restricted basin
cyclic sedimentation - alternates green/grey to yellow shale
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Animals preserved in Chengjiang formation
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How did preservation occur at the Solnhofen limestone
+ evidence
calm, warm, shallow marine environment
cut off from the ocean and other land H2O sources
high salinity in lagoons - toxic ( if fell in animals would die) so no scavengers or bacteria - high salinity also means necrolytic features shown
anoxic preferable
rapid deposition
shallow fine grained carbonate mud + eavpourate deposists
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kind of organisms preserved
8 archeopteryx
alligatorellus
pterdactylus- flying reptile, wings formed from muscle membrane and skin stretching from 4 toe to hind legs
compsognathus
jellyfish
dragonflies
ammonites
horseshoe crabs
ectoderms
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Why are the fossils at the solhnhoffen limestone so important to evolution
Archeopteryx- missing link between birds and evolution
show feathers e.g. feathers and tail feathers + plumage around legs, bones and soft tissue
no feathers on neck
primitive shoulder gridle - limited range of motion - glided/flew short distance
broad wings
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3 parts of the Milankovitch cycle
obliquity
precession
eccentricity
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Obliquity explanation
Angle the earths axis is tilted
greater the tilt warmer the climate + less ice + more extra our seasons are as each hemisphere reaches more solar radiation in summer
larger tilt = deglaciation
every 41000 yrs
tilt doesnt change massivly due to large moon
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precession explanation
wobble on the Earths rotational axis as it rotates
due to tidal forces by sun + moon
every 23,000 yrs
makes seasonal conditions more extreme in 1 hemisphere and less in other -swaps
doesnt effect when seasons occur
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eccentricity explanation
Measure of how much earth orbit has changes shape from a perfect circle
Earths movement around the sun isnt perfectly circular - close
over time gravity pull from saturn and jupiter - varies shape - slightly elliptical
eccentricity decreases - seasons even out
increases- seasons slightly change lengths as it effects distance from the sun
closest jan 3rd furthest july 4th
every 100000yrs
when orbit is most eccentric the closest approach receives 23% more solar radiation the furthest
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History of the continent + brief description
vaalbara- 3.5Ga single small continent
Ur- 3Ga half size of aussie
Kenorland- 2.6-2.7Ga super continent
Columbia- 1.8Ga 1/3 of present land area
Rodinia- 1.0-0.6Ga super continent
Pannotia- 0.65-0.56Ga short lived super continent
Pangea-0.3-0.17Ga all of earth approx
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The formation of Pangea
southen half = Gondwanaland
formed by collisions in late cambrain
existed before pangea and after
in the carboniferous gondwanland collided with Laurasia creating pangea - variscan orogeny
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The breakup of Pangea
began to break up 200ma - early triassic
Gondwanaland split from laurasia
150ma gondwanaland broke up
Cretaceous- india moved away from antarctica heading north
south atlantic and developed
sep africa and south america
3 major phase breakup in cenozoic - North amrica/greenland (laurasia) broke free of Eurasia (60-55Ma)
Atlantic and India ocean continued to expand - closed tethys ocean
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Pre Pangea
post collision:
laurasia moved away from gondwanaland - proto- tethys ocean
laurasia rifted - lapetus ocean
early ordivician- avalonia broke off gandwanaland collided with laurasia and joined
as the lapetus closed
and gondwanaland moved south
permo-carboniferous: 3 main blocks of pagea joined (complete by ealry permian) then Gondwanaland moved west in late triassic producing classic configuration
