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ANT203H5 Lecture Notes - Electron Paramagnetic Resonance, Racemization, Atomic Number

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Esteban Parra

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ANT203Y5 – Biological Anthropology
Lecture 26 – February 27, 2014
Paleoanthropology: An Introduction
- Different fossils, where they are, many classifications of fossils and questions of fossil hunters.
What is Paleoanthropology?
-Paleoanthropology can be defined as the study of early humans. It is important to
mention that this comprises both their biology and their culture.
A Multidisciplinary Science
-Scientists from many disciplines join their efforts to obtain the most complete perspective
of human origins possible….
- Biological anthropologists, archeologists, paleontologists, paleobotanists, and geologists,
among many others.
Windows into our Past…
-Important clues about the evolution of our species can be obtained by analyzing fossil
- Here is some more information about fossils and how they form…
About Fossilization
-Fossilization is a rare phenomenon, and it is dependent of a number of important factors
affecting preservation after death, including….
-Geological factors: Nature and composition of sediments.
-Temporal factors: Variation of preservation conditions through time.
-Biological factors: Role of organisms after death
-*Taphonomy is the study of the processes affecting an organism after death that result in
its fossilization.
Differential Preservation
-Plants and animals from humid tropical forests, or mountain areas are rarely preserved
due to high rates of decay or erosion.
-This is one of the reasons for the lack of fossils for the chimp or gorilla lineages.
-Also, hard parts (bones, teeth) of the body tend to be preserved, while soft parts are
usually lost.
Hominid Fossils
-Most of the hominid fossils have been found in:
oVolcanic deposits.
oLake (lacustrine) or river (fluviatile) sediments.
The Fossilization Process
-There are several ways in which fossilization can occur. Below, we indicate three
common forms.
oOrganic or inorganic material is replaced by soil minerals (e.g. calcium
carbonate, calcium phosphate).
o“The Black skull” - Early robust estrolopithises (ehtiopia). The black skull name
comes the black and blue color of the skull because of the skull preserved in soil
with manganese.
-Cast and mold
ANT203Y5 – Biological Anthropology
Lecture 26 – February 27, 2014
oCaused by deposits of sediment in cavities of the organism, resulting in a three
dimensional model.
oThe Taung Child –Estolopithicus Africanus; discovered by Raymond Darke.
When he saw this fossil in S. Africa, the skull was primate like, whereas the face
was human like.
oTwo-dimensional imprints most commonly found in silt or clay, without organic
material present.
oLitalie footprints: are around 3 million years ago. We know that hominids were
walking bipedially as far back as 3.6 million years ago
Dating the Fossils
-Finding a fossil (lucky you!) is just the first step of a long process, and there are many
other things to do.
-The next key step is to determine the age of the fossil. This is critical to put together the
complicate puzzle of human evolution
Dating Methods
-Two main categories:
-Relative methods: They give the time of a fossil or artifact with reference to another
fossil, artifact, or event. They don’t provide absolute dates.
-Chronometric (or absolute) methods: They provide estimates of the actual age of the
Relative Dating Methods
-Stratigraphic dating: Based on the geological principle of superposition: The deeper the
layers of deposits, the older.
-Problems with Stratigraphic Dating
oMethod is only relative.
oNot valid for sites with different stratigraphy.
oPossible problems due to disturbance of the layers (for geological reasons, or
human or animal action)
Fluorine Analysis
-Based on chemical changes of skeletal remains buried in the earth
-Fluorine is an element that is found in ground waters
-With time, the amount of fluorine in the bone increases (and the amount of nitrogen
-Problems with Fluorine Analysis
oRelative method doesn’t provide absolute dates.
oDifficult to compare bones from different sites, because fluorine content can
vary in the water.
Fluorine Test and Piltdown (not part of the slides)
-As we have seen, Fluorine analysis can indivate if different bones from the same site
correspond to animals that ived approx.. at the same time
-The fluorine test was used by Oakley to uncover the Piltdown hoax: cranium and jaw had
different fluorine context. Other animal bones were much older than the skull or jaw.
ANT203Y5 – Biological Anthropology
Lecture 26 – February 27, 2014
oWas used to unconver the famous Piltdown hoax
Biostratigraphy (Index Fossils)
-Relative dating of hominid fossils can be carried out using as a reference fossils of
animals that lived only during a specific period of time in the past.
-This method has been very useful in places where it is difficult to obtain absolute dates,
such as South Africa.
-Paleomagnetism: When lava cools down, the iron particles become magnetized
according to the position of the North pole at the time.
-It is known that the earth magnetic pole has been reversed several times during the last
2.5 million years.
-Hominid fossils can be roughly dated by the location of the hominid site with respect to
the known magnetic reversals
Other Relative Dating Methods
-Pollen Analysis: Use of microscopic pollen grains or spores to date human sites.
-Seriation: Dating method based on how artifacts change with time.
Chronometric (Absolute) Dating Methods
-Radiometric methods: This category comprises several widely used dating methods, all
of which are based on the decay of radioactive isotopes with time.
oThey are unstable, and will decay over time
-Isotopes are forms of chemical elements that have the same atomic number (number of
protons) but differ in mass (different number of neutrons).
More on Radiometric Methods
-Some isotopes (radioactive isotopes) are unstable, and with time will be transformed
into other elements. Each radioactive isotope has a different rate of decay, which is
measured as its half-life (the time required for half the original atoms to decay).
oThese are used for dating
Potassium-Argon Method
-This method can be used to date very old sites (several million years old). It is based on
the transformation of potassium-40 into argon-40.
-The half-life of potassium-40 is around 1.26 billion years (1.26 109).
-Usually, the Potassium-Argon method is used to date volcanic rock or ash deposits,
because they have comparatively large amounts of potassium. This method has been
widely used in East African sites.
-Example of the application of the Potassium-Argon method
Radiocarbon Method
-Widely used to date relatively young sites. It’s based on the decay of Carbon-14, which
has a half-life of approximately 5,730 years.
-Carbon-14 is produced in the atmosphere, and is absorbed by animals and plants. When
they die, the process of decay begins.
-The Carbon-14 method is normally used to date sites younger than 60,000 years old.