Presentation on theme: "2. The discovery of the past"— Presentation transcript:
1 2. The discovery of the past 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)Charles LyellGeorges CuvierEarly paleontology mainly described ancient life within the Linnean frameworkModern paleontology tries to reconstruct ancient life.It links therefore ecology and taxonomy.Mary Anning ( )Richard Owen ( )
2 How do animals fossilize? Taphonomy (Greek: tafos: burial; nomos: law)Immediate burialLiving organismDeathFossilRemainsBuried remainsMineralizationDecomposition Decay BleachingDelayed burialExposed remainsStratinomyGinkgo bilobaGinkgo adiantoidesMuch less than 1% of all organisms fossilizeCoral fishCoral fish from JuraBioerosion
3 Fossilized Cyanobacteria (stromatolites) from South Africa A fossil forest in Dorset, England formed by fossilized bacteria around old tree stumps.Fossilized Cyanobacteria (stromatolites) from South AfricaA fossilized dinosaur footprint from New MexicoA mammoth coprolith (fossilized excrements)
4 Immediate and delayed buriages From B. Ziegler: Allgemeine Paläontologie. Thieme, 1975.
5 What fossilizes? Hard body materials Soft body materials Substance ExamplesCalcite (CaCO3) Octocorallia Bryozoa Brachiopoda Polychaeta Ammonita Belemnita EchinodermataAragonite (CaCO3) Hydrozoa GastropodaCalciumphosphate Vertebrata (Ca5(OH)(PO4)3) Trilobita CrustaceaOpal (SiO2.H2O) Radiolaria Diatomea PoriferaChitin Algae Fungi Arthropoda Cnidaria Priapulida AnnelidaCellulose Plantae TunicataSoft tissues very seldom fossilizeExceptions areFast drying out in very arid climatesPermanent frozenPreservation in amber or asphaltA feathered Dinosaur:Sinosauro-pteryx
6 How complete is the fossil record? Without hard skeletonFossilsWith hard skeletonFossilsCephalochordataUnknownVertebrataOftenTunicataRareEchinodermataOftenChaetognathaRareTentaculataOftenPentastomidaUnknownArthropodaOftenTardigradaUnknownMolluscaOftenOnychophoraRareCnidariaOftenPogonophoraUnknownPoriferaOftenSipunculidaRareRhizopodaOftenEchiuridaUnknownHard skeleton infrequentNematodaRarePlathelminthesUnknownBranchiotremataSome taxa oftenCtenophoraUnknownAnnelidaSome taxa oftenMesozoaUnknownCiliataSome taxa oftenSporozoaUnknownFlagellataSome taxa often
7 Under what conditions do organisms fossilize? Probability of fossilizationMoisture gradientNutrient rich soilsRiver sedimentsAnaerobic conditions (moorlands)Volcanic ashesSalinity gradient
8 How complete is the fossil record? Benton MJ, Willis MJ, & Hitchin R Quality of the fossil record through time. Nature 403:Divergence time inferred from cladogramDivergence time inferred from fossilsSCI: Quotient of consistent to inconsistent nodesRCI: Relative completeness indexGAP: Gap excess indexAlba DM, Jordi A, Moya-Sola S Completeness of mammalian fossil record in the Iberian neogene. Palaeobiology 27: 79-83Neogene Iberian mammalsThe 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:Species level: 77%Genus level: 91%
9 The tectonic plates (from David Sanfwell, Scripps Inst. Oceanography) Continental driftAlfred Lothar Wegener ( )The tectonic plates (from David Sanfwell, Scripps Inst. Oceanography)Evidence for plate tectonics:Fit of coastlinesDistribution of mountainsContinuity of fossilsContinuity of geological featuresIsostasy: Earth acts like a fluidFrom Press et al Understanding earth,
12 Relative dating methods Fossil datingRelative dating methodsRelative dating uses geological strata to infer whether fossils are older or younger than a given stratumLayer 1YoungerLayer 2TimeLayer 2OlderStratigraphyMorphological primitivism
13 Absolute dating methods Radiometric datingMost 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)muscoviteamphiboleglauconiteVolcanic rocksSometimes in sedimentsUranium may be found in:zirconurananitemonaziteapatitespheneCarbon 14 is used for bones
14 How to use radiometric dating? The Rb/Sr System= 1.42 x a-1, t1/2 = 4.8 x 1010 ab-decayPt: Amount of daughter atoms through decayTotalDecayOriginal86Sr is an isotope that isnot radioactivenot radiogen
15 Recognition of unique events to subdivide time Radiometric datingStratigraphyRelative time scaleAbsolute time scaleGeological time scaleRecognition of unique events to subdivide timeCalibrating geological timeRadiomtric dating of layersRaw dataModified from Andy MacRae: Radiometric Dating and the Geological Time Scale.
16 Dendrochronology analyses tree-ring growth patterns. Fission trackDendrochronologyFission 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.
17 History of the earth Steno founded stratigraphy by stating that geological layers are horizontal and superposed.Deeper layers are older.Nicolas Steno ( )The Red Rock Canyon, California
18 The geological time scale EonEraPeriodAge at Base (Mya)Duration (Mya)PhanerozoicCenozoicQuaternary1.6Tertiary6563.4MesozoicCretaceous14075Jurassic205Triassic25045PaleozoicPermian29040Carboniferous355Devonian41055Silurian44030Ordovician51070Cambrian540ProterozoicNeoproterozoicEdiacaran (Vendian)63090Cryogenian850220Tonian1000150Mesoproterozoic1600600Palaeproterozoic2500900Archean38002950Hadean4550750
19 Today’s readingHistory of palaeontology:History of earth:Radiometric dating details:Geological time scale: