2. The discovery of the past
Georges Cuvier
Charles Lyell
To study evolution means to dig in the past.
The science of past organims is paleontology (greek: palaews:
old, logos: science)
Paleontology deal with fossils (lat. fodere = to dig)
Early paleontology mainly described ancient life within the Linnean framework
Modern paleontology tries to reconstruct ancient life.
It links therefore ecology and taxonomy.
Mary Anning (1799-1847) Richard Owen (1804-1892)
How do animals fossilize?Taphonomy (Greek: tafos: burial; nomos: law)
Living organismDeath
Remains
Exposed remains
Buried remains
Stratinomy
Decomposition DecayBleaching
Delayed burial
Immediate burial
Ginkgo biloba Ginkgo adiantoides
Much less than 1% of all organisms fossilize
Coral fish Coral fish from Jura
FossilMineralization
Bioerosion
A fossil forest in Dorset, England formed by fossilized bacteria around old tree stumps.
Fossilized Cyanobacteria (stromatolites) from South Africa
A mammoth coprolith (fossilized excrements)A fossilized dinosaur footprint from New Mexico
From B. Ziegler: Allgemeine Paläontologie. Thieme, 1975.
Immediate and delayed buriages
Hard body materials Soft body materials
What fossilizes?
Substance ExamplesCalcite (CaCO3) Octocorallia
BryozoaBrachiopodaPolychaetaAmmonitaBelemnitaEchinodermata
Aragonite (CaCO3) HydrozoaGastropoda
Calciumphosphate Vertebrata (Ca5(OH)(PO4)3) Trilobita
Crustacea
Opal (SiO2.H2O) RadiolariaDiatomeaPorifera
Chitin AlgaeFungiArthropodaCnidariaPriapulidaAnnelida
Cellulose PlantaeTunicata
Soft tissues very seldom fossilize
Exceptions are
Fast drying out in very arid climates
Permanent frozen
Preservation in amber or asphalt
A feathered Dinosaur:
Sinosauro-pteryx
Vertebrata
Echinodermata
Tentaculata
Arthropoda
Cnidaria
Porifera
Branchiotremata
Annelida
Flagellata
Ciliata
Cephalochordata
Echiurida
Tunicata
Chaetognatha
Plathelminthes
Pentastomida
Nematoda
Tardigrada
Onychophora
Pogonophora
Sipunculida Rhizopoda
Ctenophora
Mesozoa
Sporozoa
Without hard skeleton With hard skeleton
Hard skeleton infrequent
Fossils Fossils
Unknown
Unknown
Rare
Rare
Unknown
Unknown
Rare
Unknown
Rare
Unknown
Rare
Unknown
Unknown
Unknown
Often
Often
Often
Often
Often
Often
Some taxa often
Some taxa often
Some taxa often
Some taxa often
Often
Mollusca Often
How complete is the fossil record?
Under what conditions do organisms fossilize?
Volcanic ashesAnaerobic conditions(moorlands)
River sediments
Moisture gradient
Nutrient rich soils
Probability of fossilization
Salinity gradient
How complete is the fossil record?
Neogene Iberian mammals The completeness of the fossil record PT can be calculated from the probability R that a fossil species is preserved at least in one
geological layer:n
T qT 1 qTT
T 1
P [1 (1 R )(e e )]
Species level: 77%
Genus level: 91%
00.10.20.30.40.50.60.7
0 5 10 15 20 25 30
Met
rics
PZ PZ/MZ MZ/CZNZ CZOlder ------ Younger
RCI
GER
SCI
Speciesy = -0.88x + 6.5
Generay = -0.37x + 5.03
0
1
2
3
4
5
6
7
0 2 4 6 8 10 12 14
Actual range
ln R
SCI: Quotient of consistent to inconsistent nodes
RCI: Relative completeness index
GAP: Gap excess index
Divergence time inferred
from cladogram
Divergence time inferred from fossils
Benton MJ, Willis MJ, & Hitchin R. 2000. Quality of the fossil record through time. Nature 403: 534-537.
Alba DM, Jordi A, Moya-Sola S. 2001. Completeness of mammalian fossil record in the Iberian neogene. Palaeobiology 27: 79-83
Continental drift
Alfred Lothar Wegener (1880-1930)
The tectonic plates (from David Sanfwell, Scripps Inst. Oceanography)
Evidence for plate tectonics:
Fit of coastlines
Distribution of mountains
Continuity of fossils
Continuity of geological features
Isostasy: Earth acts like a fluid
From Press et al.. 2004. Understanding earth, http://www.whfreeman.com/presssiever/con_index.htm?99iex
From C. R. Scotese: http://www.scotese.com/future.htm
Continental drift
How to match phylogeny and plate tectonics
Tinamou
Moa
Rhea
Ostrich
Kiwi
Emu
Cassowary
New Guinea
Australia
South America
New Zealand
Africa
79
69
65
62
35
100
82
55
0.1
Relative dating methods
Relative dating uses geological strata to infer whether fossils are older or younger than a given stratum
Layer 1
Layer 2
Layer 2
Time
Older
Younger
Stratigraphy
Morphological primitivism
Fossil dating
Absolute dating methods
Radiometric dating
0
0.2
0.4
0.6
0.8
1
0 3.4657 6.9314 10.3971 13.8628 17.3285 20.7942
Time [half times]
Dec
ay
y
Surviving atoms
Daughter atoms
y=e-kt
t = ln(y)/kHalf time
Radioactive Element Stable element Half timePotassium 40 Argon 40 1.25 billion yrsRubidium 87 Strontium 87 48.8 billion yrsThorium 232 Lead 208 14 billion yearsUranium 235 Lead 207 704 million yearsUranium 238 Lead 206 4.47 billion yearsCarbon 14 Nitrogen 14 5730 years
Most minerals which contain radioactive isotopes are in igneous rocks.
The dates they give indicate the time the magma cooled.
Potassium 40 is found in: potassium feldspar (orthoclase)
muscovite amphibole glauconite
Volcanic rocks Sometimes in sediments
Uranium may be found in: zircon
urananite monazite apatite sphene
Volcanic rocksCarbon 14 is used for bones
How to use radiometric dating?
The Rb/Sr System 87 8737 38Rb Sr 87 87 t
t 0Rb Rb e l
t 0 t
t tt t t t
P N N
P N e N N (e 1)l l
b-decay
l = 1.42 x 10-11 a-1, t1/2 = 4.8 x 1010 a
87 87 t 87t t 0Sr Rb (e 1) Srl
87 87 87tt t 0
86 86 86t t t 0
Sr Rb Sr(e 1)Sr Sr Sr
l
87t
86t
SrSr
87t
86t
RbSr
tslope (e 1)l
870
86t 0
SrSr
4x x3 xe 1 x ... 1 x;x 1
3! 4!
87 87t 0
87 87 87 86 86t t 0 t t 0
8786 86 86tt t t 0
86t
Sr SrSr Rb Sr Sr Sr1t t
RbSr Sr SrSr
l
l
tt 0N N e l
Pt: Amount of daughter atoms through decay
Total OriginalDecay
86Sr is an isotope that is• not radioactive• not radiogen
Modified from Andy MacRae: Radiometric Dating and the Geological Time Scale. http://www.talkorigins.org/faqs/dating.html
Raw dataRecognition of
unique events to subdivide time
Radiomtric dating of layers
Calibrating geological
time
Stratigraphy Relative time scale
Absolute time scale
Geological time scale
Radiometric dating
Fission track Dendrochronology
Fission Tracks (FT) are micrometer-sized, linear damage tracks that occur in insulating
minerals and that are caused by the spontaneous fission of heavy, unstable
nuclides (mostly 238U in natural minerals).
Dendrochronology analyses tree-ring growth patterns.
History of the earth
Nicolas Steno (1638-1686)
Steno founded stratigraphy by stating that
geological layers are horizontal and superposed.
Deeper layers are older.
The Red Rock Canyon, California
The geological time scale
Eon Era Period Age at Base (Mya) Duration (Mya)Phanerozoic Cenozoic Quaternary 1.6 1.6
Tertiary 65 63.4 Mesozoic Cretaceous 140 75 Jurassic 205 65 Triassic 250 45 Paleozoic Permian 290 40 Carboniferous 355 65 Devonian 410 55 Silurian 440 30 Ordovician 510 70 Cambrian 540 30
Proterozoic Neoproterozoic Ediacaran (Vendian) 630 90 Cryogenian 850 220 Tonian 1000 150 Mesoproterozoic 1600 600 Palaeproterozoic 2500 900
Archean 3800 2950Hadean 4550 750
History of palaeontology: http://en.wikipedia.org/wiki/History_of_paleontologyHistory of earth: http://wiki.cotch.net/index.php/History_of_the_EarthRadiometric dating details: http://www.tulane.edu/~sanelson/eens211/radiometric_dating.htmGeological time scale: http://en.wikipedia.org/wiki/Geologic_time_scale
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