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Understanding Earth Sciences > Palaeontology > Flashcards

Palaeontology Flashcards

1
Q

The fossil record:

FIRST EVIDENCE OF ORGANIC LIFE

A
  1. 1 GA
    - Zircon crystals with with high 12C ratio in carbon class
    - Jack Hills, Australia
    - life prefers lighter C
  2. 7 GA
    - BIFS
    - Isua, Greenland
    - require oxygen, produced in photosynthesis

Stromatolites
- rock like structures formed by bacteria

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2
Q

The fossil record:

BODY FOSSILS

A
  1. 43 GA
    - Strelley Pool Chert
    - Australia
    - contains ‘petrified’ sulphur-reducing bacteria
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3
Q

The fossil record:

EUKARYOTES

A

1600 MA

Small carbonaceous fossils with a distinct morphology

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4
Q

The fossil record:

FIRST SEXUALLY PRODUCING ORGANISM

A

1050 MA

  • Bangiomorpha Pubescens
  • Arctic Canada
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5
Q

The fossil record:

FIRST BIOMARKERS

A

750 MA

24-isopropylcholestone

  • produced by sponges
  • ALSO produced by seaweed; weakens claim as a biomarker
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6
Q

The fossil record:

FIRST ANIMALS

A

555 MA

Sponges

  • Australia and Russia
  • macroscopic scale (cm) mouldic preservations

TRANSFORMED THE OCEANS BY FILTERING OUT AND ALLOWING BIODIVERSITY

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7
Q

The fossil record:

FIRST SKELETONS

A

545 MA

Small Shelly Fossils (SSFs) called Cloudina

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8
Q

The fossil record:

FIRST FORESTS

A

400 MA

Devonian trees

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9
Q

Unusual preservation methods and examples

A

Amber preservation

  • insects
  • 140 Ma to recent
  • tree resin

Ice preservation

  • mammoths
  • 10Ka
  • oldest ice 1.2 Ma
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10
Q

Why is the fossil record biased?

A

DECAY

SCARCITY

SEDIMENTATION

ECOLOGY

CHEMISTRY

DIAGENESIS

METAMORPHISM

OUTCROP

COLLECTION

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11
Q

Preservation potential; decay

A

Reduces available info e.g. colour/soft tissue

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12
Q

Preservation potential; scarcity

A

If more common, fossilisation more likely e.g. humans/ants, not pandas

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13
Q

Preservation potential; sedimentation

A

Land erosion dominated

Ocean sedimentation dominated = more appropriate for fossilisation

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14
Q

Preservation potential; ecology

A

High energy environments e.g. foreshore will destroy fossils

Low energy environments e.g. estuarine muds will encourage

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15
Q

Preservation potential; chemistry

A

Acidic/anoxic

Anoxic environments will preserve soft parts because there are no break-down organisms

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16
Q

Preservation potential; diagenesis

A

Two scenarios:

  1. Decreases preservation potential because mud is squeezed through the shell and dissolves/displaces the fossil
  2. Increases preservation potential because a mineral e.g. pyrite forms on the outside of the shell like a protective layer
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17
Q

Preservation potential; metamorphism

A

Unrecognisable

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18
Q

Preservation potential; outcrop

A

May/may not be visible

e.g. in Permean times there are few marine fossils, however there are also few marine rocks known

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19
Q

Preservation potential; collection

A

E.g. China only recently discovered feathered dinos

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20
Q

Darwin’s theory of evolution

A

Natural selection

Opposed by CATASTROPHISM, Cumber 1976

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21
Q

Darwin’s obstacles

A
  1. Absence of intermediate forms

2. Cambrian explosion

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22
Q

Absence of intermediate forms

A

Primitive and complex organisms with no fossil link

Both alive at the same time = don’t evolved from one another
= 3rd unknown in the past which is ancestral to both
- more simple than either i.e. not an intermediate
- not hard/fast split, many dead ends along the way

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23
Q

The tree of life

A

Thins out very quickly
- not all fossils have direct ancestors that survive to this day

Further back in time = fewer fossils are members of current living taxa; more are extinct

“The tree of life is dominated by dead ends”

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24
Q

Possible reasons for the Cambrian Explosion

A

ENVIRONMENTAL CHANGE

  • not possible
  • looked at different locations around the world and found this was not the case

TAPHANOMIC EVENT

  • = missing fossils due to preservation issues
  • shell dissolution etc
  • BUT this was because the only fossils available in Darwin’s time for SSFs
  • NOW lots of other fossilisation modes available
  • weakens argument as they show same Cambrian explosion

So now we believe it was ?due to a small atmospheric rise in oxygen
- Ediacaran atmosphere lacked O2 (sea floor sediment evidence)
- 15-40% of present level
N.B. ENOUGH FOR SPONGES…

Did life drive change? “POSITIVE FEEDBACK”

Sponges, once evolved, could pump and mix O2 to deeper waters
Small increase in O2 lead to the gradual emergence of predators = diversification for survival e.g. Cloudina grew hard, mineralised exoskeletons

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25
Q

Other types of fossilisation

A

Small carbonaceous fossils

Exceptional fossilisation

Burgess-Shale

Ediacara-type

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26
Q

Small carbonaceous fossils

A

NOT mineralised

Same taxa as SSFs

Simple in Ediacaran to diverse/complex in Cambrian

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27
Q

Exceptional fossilisation

A

Preserve cellular-level detail of microscopic fossils

Fossil Lagerstätten:

  1. Concentration (large no.s)
  2. Conservation (amazing detail)

e.g. phosphatisation

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28
Q

Burgess-Shale

A

Soft tissue present in a white clay mineral
Shallow marine organisms swept into deep sea settings by turbidity currents

Ediacaran = seaweed-grade organisms
Cambrian = animals
29
Q

Ediacara-type preservation

A

Microbial mats of blue-green algae (in O2-starved areas) overgrew soft-bodied organisms on a soft muddy seabed
Influx of sand then produced casts/moulds

e.g. Dickinsonia

N.B. Not photosynthetic organisms

  • disappeared when sponges came in
  • ?they cleaned the water of nutrients
30
Q

Moving onto land:

PALAEOSOILS

A

2760MA

Rich in organic matter

31
Q

Moving onto land:

Fossil evidence of life outside oceans

A

1060MA

Microfossils in Nonesuch Shale, N USA

32
Q

Moving onto land:

INCREASE IN LAND WEATHERING

A

850MA

Evidence = change in carbon isotope signatures

Due to microbes

N.B. INDIRECT EVIDENCE

33
Q

Moving onto land:

TRACE FOSSILS (AND MORE SOIL)

A

510MA

Climactichnites found in tidal/beach settings - refuge concept?

Also soils depleted in phosphorous due to the presence of fungus

34
Q

Moving onto land:

FIRST DIRECT EVIDENCE OF LIFE ON LAND

A

460 MA

Trilete spores with trilete mark retained

  • suggests hardened in terrestrial environment to protect from desiccation
  • made of sporopollenin (tough biopolymer) = :) fossilisation
35
Q

Moving onto land:

FIRST FOSSILS OF TERRESTRIAL ORGANISMS

A

444MA

Tortotubus 
= underground fungus network
- infiltrated regolith
- increase soil stability
- increase bedrock weathering
N.B. Since funghi decompose things, there must have been something for them to decompose?
36
Q

Moving onto land:

FIRST LAND PLANTS

A

432 MA

Cooksonia

= a TRACHEOPHYTE

  • vascular tissue = transports water through stems
  • impermeable cuticle layer which closes during desiccation and stomata allow CO2 in/out
  • tough vessels (water pressure) = can grow upwards
37
Q

Moving onto land:

TRACE FOSSILS OF LAND DWELLING ORGANISMS

A

428MA

Pneumodesmus = terrestrial millipedes

38
Q

Challenges getting onto land

A

Osmosis/gas exchange
- most marine organisms in osmosis with nutrients in sea water

Pressure difference

Desiccation

Gravity/movement

UV radiation
- at depth = shielded

Reproduction
- many expelled into the water

Food

N.B. Could have provided a refuge away from predators e.g. Crabs lay eggs on the beach in moonlight

39
Q

How did afforestation/land plants change the atmosphere?

A
  • Caused in increase in O2 due to oxygenic photosynthesis
- = reached 13% of atmosphere = FIRE
Wildfire = charcoal plants

(By Devonian land plants were firmly established and in the early Silurian effects were detected in sedimentary systems)

  • more clay/soil production
  • less runoff
  • less sediment erodibility
  • less feldspar abundance in sedimentary deposits (converted to quartz/clay in weathering)
  • braided rivers with unconsolidated banks&raquo_space;> meandering rivers with lateral accretion sets and root traces in bank deposits
  • more stable groundwater sources = trunks reinforced by sturdy lignin molecules
40
Q

Devonian forests; impact

A

1st source of coal deposits

  • lignin&raquo_space;> kerogen/coal due to rapid burial in O2-poor sediments
  • transferred carbon from the atmosphere to the stratigraphic record

N.B. WE ARE QUICKLY REVERSING THIS TRANSFER TODAY

41
Q

Arctic Ocean Background

A

Linked to N Atlantic by Fram Strait - opened 17.5MA

49MA low sea levels cut off Arctic Ocean entirely

CO2 was high ~3500ppm

10-15 degreesC average annual temps at the poles

Warm/salt-free freshwater inputs (rain/melting winter snow)

= LOW DENSITY NEPHELOID LAYER

42
Q

Effect of a nepheloid layer in the Arctic Ocean

A

Inhibits mixing as water is not dense enough to maintain convection
= stratified
- deep waters = cold, dense, saline and ANOXIC

43
Q

“The Azolla event”

A

Azolla = freshwater fern
= ‘superplant’ with ASEXUAL REPRODUCTION
- “can double its biomass every 2-3 days in 20-hour warm days of Arctic summer”

Top layer of Arctic = freshwater and rich in nutrients due to continental weathering
= built up

Sank to anoxic deep water = didn’t decay
= sequestered 10,000 x more carbon than we have in our atmosphere today
= 3900-650ppm

CRETACEOUS GREENHOUSE WITH EXTENSIVE FLOODING OF CONTINENTAL SURFACES&raquo_space;> PRESENT ICEHOUSE WORLD

44
Q

Evidence of Azolla

A

Glacial dropstones after azolla event

8m thick organic-rich sediments

  • laminations of 100% azolla
  • grew in situ
45
Q

Evolution of powered flight

A

Evolved 4 times (or 3 within vertebrates)

Insects - 396 MA
Pterodactyl - 250MA
Birds - 150MA
Bats - 50MA

Wings are homologous as appendages but not as wings
= convergently derived homoplasies

K-Pg mass extinction:

  • incumbent species died creating gaps for birds
  • adaptive radiation; origin of flight made new niches available and led to an immediate diversification of birds
46
Q

Homoplasy =

A

Character shared by a set of species but not in their common ancestor i.e. originated independently

47
Q

Archaetopteryx

A

Oldest bird 160MA

Intermediate between birds and dinosaurs - therapods

48
Q

Types of dinosaur

A

SAUROPODS

  • long tails/necks
  • veggie

ORNITHISCIANS
e.g. stegosaurus/triceratops

THERAPODS
e.g. T-Rex/velociraptor

49
Q

Evidence for birds evolving from dinosaurs

A

ANATOMY

RESPIRATORY SYSTEM PREFERENCES

GENETIC SEQUENCES

FEATHERS

50
Q

Evidence for birds evolving from dinosaurs:

ANATOMY

A

Arm joints
- fold up into chest

Skulls

  • large brain chamber and eye sockets
  • for coordination and senses

Furcula

  • “wishbone”
  • strengthens ribcage

Tail

  • birds have squashed vertebrae
  • reduced therapy feature

Bones between ribs

  • strengthen for e.g. water diving
  • increases respiratory efficiency

Enlarged sternum
- greater respiratory capacity

51
Q

Evidence for birds evolving from dinosaurs:

RESPIRATORY SYSTEM PNEUMATICS

A

Flexible bellow-like reservoirs = pump air through inflexible lungs

CAUDAL air sac = fresh air

CRANIAL air sac = stale air

= access to oxygen when breathing in AND out
= more efficient

Blood flow opposes air flow

As with some therapies, birds have hollow bones = more space for air

52
Q

Evidence for birds evolving from dinosaurs:

GENETIC SEQUENCES

A

Protein collagen can preternaturally survive for at least 200 million years = original genetic sequencing reconstruction possible

Antibodies that bind to chicken collagen also respond to T-Rex collagen (although ?contamination issues)

Ornithischian protein sequences contain some crocodile characteristics and bird characteristics

53
Q

Evidence for birds evolving from dinosaurs:

FEATHERS

A

Jurassic dinosaurs had small ‘bristle’ feathers for insulation/camouflage
e.g. Therapod: Sinosauropteryx
Ornithischian: Kulindadromeus

Found in amber fossils

EXAPTATION CONCEPT

54
Q

Exaptation =

A

Process by which features acquire functions for which they were not originally adapted or selected

55
Q

Original uses of wings

A

Ornithomimus - mating

  • bright colours preserved by melanosomes e.g. Anchiornis
  • Wing Assisted Incline Running, not flying

Oviraptor - keep eggs warm

56
Q

Permo-triassic mass extinction

A

Largest of all time

17% marine orders extinct

52% marine families extinct

At least 75% of species extinct

  • pre 45,000-240,000
  • post 1800-9600

~251MA

Two pulses:

  1. Latest Permian 252.28+/- 0.08 Myr
  2. Earliest Triassic 252.10+/- 0.06 Myr
57
Q

Who suffered in the Permo-Triassic extinction?

A

Corals (tabulate/rugose)
Trilobites

Brachiopods
Crinoids
Bryozoans

Insects
Tetrapods
Plants

58
Q

Kill mechanisms in the Permo-Triassic extinction

A

High temperature

High CO2 levels

Anoxia

59
Q

Extinction =

A

Process of becoming extinct; of a species/family/larger group to have no living members

60
Q

Kill mechanisms; high temperature

A

Warm surface water inhibited circulation = deep waters nutrient rich

Evidence of continental weathering from High 87Strontium:86Strontium
Tropical rainfall and runoff killed plants

Nutrient rich runoff = eutrophication

61
Q

Kill mechanisms; high CO2 (RAPID!)

A

Ocean acidification due to CO2 dissolution = carbonic acid

Hypercapnia (200ppm greater than ambient CO2 for several weeks) decreased growth/survival/reproduction

Those with ‘passive’ calcareous skeleton formation didn’t survive:

  1. 86% of genera with carbonate skeletons without physiological buffering went extinct
  2. 54% of those with potential physiological buffering
  3. 4.7% with little/no carbonate shell e.g. conodants/fish/polychaete worms

ALSO those with:

  • low metabolic rate
  • limited circulatory systems
  • simple respiratory structures (CO2 inhibits the Bohr effect in ammonoids - 79% of these went extinct)
62
Q

Kill mechanisms; anoxia (evidence and causes)

A

Evidence:

  • demise of burrowing
  • organic/pyrite-rich horizons at P/Tr boundary in rocks

Causes:

  • decrease in the intake of O2 by the oceans
  • high respiration rates using O2 by organisms/decay
63
Q

Clathrates =

A

Methane hydrates
“Methane ice:
- narrow temperature/pressure stability fields
- small changes = major releases = high levels of LIGHT C I.E. 12C into the oceans

64
Q

Causes of a high 12C:13C/extinction:

A

METHANOSARCINA

IMPACTOR

VOLCANISM

65
Q

Causes of a high 12C:13C/extinction:

METHANOSARCINA

A

Bacterium which makes organic matter into methane

Then, higher temps = CO2

BUT

  • molecular clocks not very accurate
  • nickel-based bacterium; why so much Ni?
  • scale difficult to constrain
66
Q

Causes of a high 12C:13C/extinction:

IMPACTOR

A 
Iridium-rich layer near P-Tr boundary
Only major source is extra-terrestrial
BUT
- not significant amounts
- 1m BELOW boundary layer
- no evidence of a crater

6-15cm thick claystone breccias could have been ejected during the impact
BUT
- could just be reworked soils

Glassy spherules of ‘shocked’ quartz veins
BUT
- rarer/smaller than at K-Pg extinction
- could be mountain formation/volcano heat causing ash particles to melt

67
Q

Causes of a high 12C:13C/extinction:

VOLCANISM

A

Siberian traps = large igneous province of 1-4 million km3 of lava

Enough for

  • poisonous gas/acid rain/CO2 = mutant spores due to halogen gases attacking the ozone layer
  • lava to melt permafrost and sublimate frozen clathrates
  • lava to encounter coal deposits and start sooty fires

Evidence of high levels of mercury in shallow (associated with biomass/soil) AND DEEP waters = mercury poisoning

68
Q

The Fossil Record: summary

A

4.1Ga/3.7Ga
Evidence of organic life

3.43Ga
Strelley

1600Ma
SCFs

1050Ma
Sexually reproducing

750Ma
Biomarkers

555Ma
Sponges

545Ma
SSFs

400Ma
Forests

69
Q

Life on land: Summary

A

2760Ma
Palaeosoils

1060Ma
Nonesuch shales

850Ma
Weathering

510Ma
Soil and climactichnites

460Ma
Trilete

444Ma
Tortotubus

434Ma
Cooksonia

428Ma
Pneumodesmus

Understanding Earth Sciences (8 decks)

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