Presentation on theme: "Early Humans: Meet the Ancestors 2. Archaeological Evidence and the Limits of Knowledge."— Presentation transcript:
Early Humans: Meet the Ancestors 2. Archaeological Evidence and the Limits of Knowledge
Objectives Look at the scientific investigative tools Stratigraphy Archaeological dating methods Comparative Anatomy of Fossils DNA and Isotope analysis Artefact and Ecofact Evidence Consider the security of our interpretations.
Charles Darwin Origin of Species, 1859 The Descent of Man, 1871 Cartoon from The Hornet satirical magazine 1871
Stratigraphy Provides relative dating – separating the remote past into horizons of greater and lesser age. Boxgrove, England
Fauna Assemblages – Environmental Dating Boxgrove excavation era of strata indicated by animal bone assemblages Extinct rhinocerous, Stephanorhinus hundsheimensis Period when Britain had a climate like modern Africa Sites can be given sequence relative to each other but not a date by this method.
Radio Carbon Dating Invented c Based on the principle that C14 decays at a predictable rate Age calculation made by examining ratio of C14 and C12 Relatively short half life c years makes it accurate, but limits its range to about the last 40,000 years
Lascaux, S France Accelerator Mass Spectroscopy – very small samples. C14 dating of cave painting, targeting carbon based pigments Images date to kya Some images refreshed over thousands of years
Potassium - Argon Dating Less accurate but much greater dating range – suitable for the earliest hominids Used to date layers of volcanic rock Noble gas Argon 40 released when rock molten Any Argon 40 present must have derived from Radio Decay of Potassium
Uranium Series Dating Based on ratios between radio active Uranium isotopes and daughter products Uranium products are soluble in water. Thorium and Protractium products are insoluble in water. Calcareous deposits like limestone therefore start their existence with no Thorium or Protractium present.
Uranium 238 Series Uranium billion years Uranium ,000 years Thorium ,200 years Radium years Radon days Lead years Polonium days Lead 206 stable
Uranium 235 Series Uranium million years Protractium ,400 years Thorium days Radium days Lead 207 stable
Vartop Cave, Romania Limestone cave Neanderthal occupation dated to 62kya to 97kya by U-series. Footprints Suggests an individual 1.46 m tall
Cave Art Creswell Crags, Derbyshire Engraving Church Hole Creswell Crags U-series sampling of flowstone suggests pre- 12,800 BP
Equilibrium Level As levels of Thorium 230 increase rate at which it is destroyed approaches rate at which Thorium 230 is created by decay of Uranium 234.
Comparative Anatomy of Fossils Comparison of cranial capacity
Incompleteness Australopithecus Afarensis Best specimen Lucy Only 40 % complete No formal burials from this period. Most bodies dismembered and scattered by scavengers
Turkana Boy H. erectus, 1.5 mya Very narrow spinal column Lacked fine control of diaphragm Implications for speach Other specimens fall with range of modern humans Might be an individual with genetic defect.
New Species or or Diseased Individual Recent discovery of a new hobbit species contested H. floresiensis skull compared to modern human with the genetic disorder microcephaly. H. floresiensis frontal and temporal lobes highly developed
Dimorphism in Australopithecine Suggested Australopithecine dimorphism as compared to modern humans Hominids of different sizes now thought to represent different contemporary species
Ancient DNA Cheddar Gorge Late Palaeolithic skull 1911 DNA recovered 1990s Adrian Targett – descendant living few miles from find site Fears of contamination from modern DNA
Age Estimation Tooth Eruption can give age at death in modern humans very accurately Age can also be estimated from the state of fusion of bones of the skull and limbs
Errors in estimating age Australopithecene infant Taungs Child Age by comparison with humans 7 years Age by comparison with chimps 3 years
Comparative Anatomy - Teeth Nakalipithecus nakayamei jaw, Kenya, c 10mya Homo erectus c. 1 mya Broad grinding teeth indicate a fibrous plant diet, smaller teeth of H. erectus indicate an omnivore's diet – high value foods like fruit and meat.
Isotopes and Diet Fractionation of stable isotopes can idicate the origin of food sources. Ratios of C13 and C12 different for terrestrial and marine diets Mesolithic shell midden with human remains, Oronsay, Inner Hebrides Suggest protein almost entirely from fish, shellfish and marine mammals
Butchered animal bone, Boxgrove Homebase site – resources brought back to a central base. Sequence of cuts and knaw marks suggests human kill later scavenged by other large predators, Assessing Prey Species
Tool Use Modern chimps demonstrating tool use. Baringo Basin tools, Kenya 2.6 mya Earlier tools almost certainly being used but impossible to distinguish from naturally broken material
Inorganic Artefacts Clacton-on-Sea spear Sharpened and fire hardened shaft Earliest wooden artefact, 290 kya Associated with Homo heidelbergensis. Earlier artefacts simply have not survived.
Problems Interpretation rests on very partial survival of evidence. Measuring errors – complex procedures to measure very small differences in composition Sampling errors – contamination Most interesting statements rest on chains of inference All data is subject to a degree of doubt
Piltdown Man Hoax Discovered 1908 gravel pit East Sussex by museum Charles Dawson Published in the Journal of the Geological Society 1912, named Eoanthropus dawsoni Exposed by fluoride absorption test 1949, published 1953 in Time Medieval human skull Orang-utan jaw and chimpanzee teeth