Human Evolution Midterm: Paleoanthropology

taphonomy

processes that affect an organism after death

relative dating

• determines whether an object or layer is older or younger than other objects or provides an approximate age bracket

• stratigraphy (principle of superposition, biostratigraphy, tephrostratigraphy), paleomagnetism, FUN dating (Piltdown hoax)

stratigraphy

teh study of the layers of the earth

principle of superposition

• a lower stratum (or layer) is older than a higher stratum.

  • Limitation: disturbances shift strata and objects, making it difficult or impossible to reconstruct the geologic history

biostratigraphy

• sediments that were deposited far apart but contain the same index fossil species (extinct animal species whose dates are known) are interpreted to represent the same time period

  • Limitation: limited to specific geography areas​​

tephrostratigraphy

•  volcanic eruptions can be dated by studying layers of tephra (products of volcanic eruptions: lava, ash, pumice, and volcanic rock debris). Rocks with the same composition can be traced to the same eruption.

paleomagnetism

•  using the sequence of the reversals o the Magnetic North and Magnetic South poles, samples of sediments containing magnetically charged particles are dated

FUN dating (flourine, uranium, nitrogen)

• applied to bones to assess the amount of fluorine, uranium, and nitrogen in groundwater incorporated during fossilization; the longer a bone is in the ground, the more of these elements will be present in the fossil

  • Limitation- only useful with bones found at same location

piltdown hoax

• Charles Dawson; fabricated the “discovery” of a new hominin claiming it was the oldest extinct hominin found in Piltdown, England. Debunked through FUN dating

Chronometric (absolute) dating

provides a specific chronological age in years (or range in years)

• radiometric, non-radiometric

radiocarbon dating (C-14)

• rate of decay of the unstable isotope of Carbon-14 into the stable isotope Carbon-12. C-14 has a half-life of 5730 years, so it can be used on organic material that is between 300-50,000 years old

  • Limitation: need well preserved organic materials, materials has to be less than 50,000 years old

Potassium-Argon (K-Ar) dating

• the age of volcanic material (rock and ash). Can date material between 2,000-4.5 billion years

  • Limitations: can only be used on volcanic materials and age range can have a large margin of error

Uranium-Series Dating

• the age of limestone materials and other materials containing calcium carbonate (shell, bone, tooth enamel, etc.) Can be used on materials between 10,000-500,000 years old

  • Limitations: can only be used on calcite materials and must have careful stratigraphic sequences

Thermoluminescence (TL)

• when a material (clay, stone) is heated, minerals store energy in the form of electrons. The material continues to store more energy after it is heated as well. More light=older age. 100-200,000 years old

  • Limitation: Reheating destroys the material 

Electron Spin Resonance

• measures the amount of energy released from bones and teeth from microwave radiation. Dates material to 60,000-2 million years ago

  • Limitation: less accurate than TL

Fission Track Dating

• the age of natural (volcanic) and man-made glass based on the splitting of uranium when it is heated to high temperatures. Can date materials to 10,000-20 million years ago

  • Limitations: limited to glass, mica crystals (silicate minerals) and meteors

obsidian hydration analysis

• the age of obsidian can be determined by the amount of water that is absorbed by the edge of the flake. Can be dated up to 100,000 years old

  • Limitation: rate of water absorption depends on local temperatures and humidity levels, which are site specific

amino acid racemization

• when an organism dies, certain amino acids change (racemize) from L to D form at a steady rate until there are equal amounts of L and D types. ~100,000 years old

  • Limitation- temperature significantly affects the rate of racemization