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 A105 Human Origins and Prehistory
A105 Taphonomy and Dating Activity
 

Question 1. Laetoli footprints.
      The Laetoli footprints were made in volcanic ash by an early human ancestor.  Other sections of this ash contain footprints made by a variety of other animals.
        Part 1: What method would you use to get an absolute date for these footprints?
              K/Ar or Ar/Ar: these footprints were made in volcanic ash, a datable material.

        Part 2: How could you use the footprints of other animals to get a date for the human ancestor's footprints?  Would this be an absolute or relative date?
              You could use biostratigraphy/faunal correlation. This would be a relative date.
 

Question 2.  Upper Palaeolithic site.
      Materials recovered from this European Upper Palaeolithic site include flint artifacts, animal bones, hearths, and several human burials. There were no bone tools, pottery, or metals.  Some of the flint artifacts show signs of burning, and the sediments do not contain volcanic materials.
        Part 1: What would be your first choice of dating method and material for this site?
            You'd probably want to start with radiocarbon on the hearth or maybe on the animal bones -- it's more reliable than the other radiometric methods you could use here.  (You'd use ash from the hearth, not human bone, because the technique is destructive.)

       Part 2:  What other dating techniques and materials could be used at this site?
           You could use thermoluminescence (TL) on the burned flints or electron spin resonance (ESR) on the animal teeth.
 

Question 3. Paleomagnetism.
      Imagine yet another site, containing fossil animal bones, artifacts, and hominid fossils.  These materials were found in an archaeological layer that had volcanic ash layers above and below it.  The archaeological sediments themselves are water-lain deposits that contain iron-rich particles.
        Part 1: What material and method would you use to obtain an absolute date on the archaeological layer?
            You would use K/Ar or Ar/Ar on the volcanic ashes above and below the archaeological layer.  This would let you bracket your site between two ages.
       
        Part 2: What dating technique could be used to get a relative date using the archaeological sediments?
          Since there are iron-rich (magnetic) particles in the sediment, you could use paleomagnetism.

Question 4. "What would you expect?"
      Carefully examine the bones in piles A and B and discuss which group of bones you think would be the most likely to be found in the fossil record (hint: think about physical features of the bones and how that might relate to their durability).
        Part 1: Pick the pile of bones most likely to fossilize and provide three observations that support your answer.
          Pile A would be the most likely to fossilize.  It contains very hard, dense parts such as teeth, horns, and jaw bones.  Teeth are the most durable part of the body, and dense elements with a lot of cortical bone are more durable than those with more cancellous (spongy) bone.  Shape and size also are factors; bones that are flat are more prone to be broken up than those with more compact shapes.

Question 5.  "To fossilize or not to fossilize?"
      Assume two hominids die, one on the open savanna, and the other on an ancient lakeshore.
        Part 1: Which hominid do you think stands the best chance of being fossilized (entirely or partially)?  Part 2: Why do you think this?
          The hominid that dies on the lakeshore will have a better chance of being fossilized, because sedimentation proceeds faster there -- the quicker a bone gets buried, the better the chance it will become a fossil.  Also, the hominid on the open savanna will be more exposed to carnivores and scavengers, which tend to break, digest, and scatter bones.  Lake shores can be more protected environments.