Transcript How We Discover the Past Power Point

• Archeologists and
Paleoanthropologists
rely on four kinds of
evidence to learn about
the past:
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Artifacts
Ecofacts
Fossils
Features
• Together they provide a
detailed story about
human life long ago.
• Anything made or modified by humans is an artifact.
• Most of the artifacts that archeologists look for and
examine to reconstruct what was daily life like long ago
are accumulated garbage of daily life – This is called
archaeological records.
• The most common artifacts from the past are stone tools,
which archeologists call Lithics
• Humans first starting stone tools more than 2.5 million years
ago.
• Used for almost every purpose.
• Another common artifact is ceramic (pots and other
items of baked clay).
• Humans started making ceramics about 10,000 years ago.
• Because they are both fragile and relatively easy to make,
ceramics show up frequently in the garbage that makes up the
archeological record.
• Wood and bone artifacts are common as well.
• Used to make hide-working, cooking, hunting and even
butchering tools.
• Unlike stone tools they tend not to survive well in the
archeological record.
• Ecofacts are natural objects that have been used or
affected by humans.
• For example: bones from animals that people have eaten.
• These bones are somewhat like artifacts, but they haven’t been
made or modified by humans.
• Rare but particularly informative about human biological
evolution.
• A fossil may be an impression of an insect or leaf on a
muddy surface that is now a stone.
• Sometimes it is consist of the actual hardened remains of
an animal’s skeletal structure.
• When an animal dies, the organic matter that made up its body
begins to deteriorate.
• The teeth and skeletal structure are composed largely of inorganic
mineral salts, and soon they are all that remains.
• We don’t have fossil remains of everything that lived in
the past, and sometimes we only have fragments from
one or few individuals.
• Robert Martin established that the earth has probably
seen 6,000 primate species. Remains of only 3% of these
species have been found.
• Features are a kind of artifact, but archaeologist
distinguished them from other artifacts because they
cannot be easily removed from an archaeological site.
• Hearths are good example, when humans build a fire on bare
ground the soil becomes heated and is changes.
• When archaeologists finds
a hearth, they find an
area of hard, reddish soil
often surrounded by
charcoal and ash.
• The most common features are called pits.
• Pits are simply holes dug by humans that are later filled with
garbage or eroded soil.
• Living floors are another common type of features.
These are the places where humans lived and worked.
• A large or very deep area of such debris is called a
midden.
• Midden are often the remains of garbage dumps or areas
repeatedly used over long periods of time, such as caves.
• Buildings are a common feature on archaeological sites.
• Evidence of the past is all around us, but finding them is
not always easy.
• Archaeologists and paleoanthropologists usually restrict
their search to what is called sites.
• Sites are know or suspected locations of human activities in the
past that contain a record of that activity.
• Sites are created when the
remnants of human activity are
covered or buried by some
natural process.
• The most dramatic one is
volcanic activity.
• The records of human behavior or
humans themselves can be totally
buried within seconds.
• The most impressive example of this
must be Pompeii – an entire city that
was buried in the eruption of Mount
Vesuvius in A.D. 79.
• Today archaeologists are digging out
the city and finding the remains of
ancient life just as it was left in the
moments before the eruption.
• Less dramatic means of burring the record of human
behavior are the natural processes of dirt accumulation
and erosion.
• Wind and water-borne soil and debris can cover a site either
quickly (as in a flood) or over a long period of time.
• The processes through which soils are built up can also
bury artifacts in a way that allows archaeologists to
uncover them later.
• Since good locations to live and work in are often reused
by humans, many sites contain the remains of numerous
human occupations.
• Stratified: each layer, or stratum, of human occupation is
separated like a layer in a cake.
• Not only do stratified sites allow the archaeologist or
paleoanthropologists to distinguish the sequence of site
occupations, but the strata themselves provide a way to
know the relative ages of the occupations – earlier
occupations will always be below later ones.
• The very processes that create sites can often damage or
destroy them.
• Wind and water for example.
• Harold Dibble and his colleagues, for example, have argued that the
Lower Paleolithic site of Cagny-L’Epinette in France does not
actually contain locations where Lower Paleolithic people lived and
worked. What looks like locations of human activities were created
by water running across the site
and accumulating artifacts in
low-lying places.
• The study of the processes of site
disturbance and destruction is
called Taphonomy.
• There is no single methods
of finding sites, and indeed
many sites are found by
happenstance.
• Archaeologists and
paleoanthropologists
employ one of two basic
methods:
• Pedestrian Survey: Walking
around and looking for sites.
• Remote sensing: Much more
high-tech way of finding sites.
• A number of techniques are used to enhance the
effectiveness of pedestrian survey.
• Use of sampling and systematic surveying methods to reduce
the area to be covered by foot.
• By focusing their search on places humans are likely to have
occupied.
• Archaeologists find archaeological deposited by sensing
their presence from a remote location, usually the current
surface of the ground beneath which the archaeological
deposits are buried.
• Most remove sensing techniques are borrowed from
exploration geology, and are the same ones geologists use
to find mineral or oil deposit.
• Only one way to recover artifacts and fossils –excavation.
• Excavation is a complex process with two goals:
1. To find every scrap of evidence.
2. To record the horizontal and vertical location of that evidence
with precision.
• Few sites can even be fully excavated. The cost involved
would be tremendous, and most archeologists feel it is
important to leave some archeological deposits
undisturbed for future archaeologists using new
techniques.
• As a result archaeologists
usually use some method
of sampling.
• Sampling however
requires that
archaeologists
carefully plan where
excavations will be
conducted so that all
areas of the site have
an equal likelihood of
being examined.
• To date, no one has figured
out a way to recover
artifacts and fossils without
destroying the site in the
process.
• For this reason most
excavation by professional
archaeologists today is
done only when a site is
threatened with
destruction.
• Once archaeologists have found a site and recovered
artifacts and other materials from it, they are ready to
begin “reading” what they have found to learn the story of
the past.
• The reading of the archaeologists is called analysis.
• Much of what is lost and discarded by humans never
survive. Much of what does survive comes to us in
fragments and in a fragile, deteriorated state.
• Before doing analysis, then, archaeologists and
paleoanthropologists must first conserve and reconstruct
the materials they have
found.
• Conservation is the process of treating artifacts to stop
decay and if possible, reverse the deterioration process.
• Some conservation is very simple, involving only cleaning
and drying the item.
• Some conservation is highly complex, involving longterm chemical treatment and
long-term storage under
controlled conditions.
• The 5,000 year-old “Ice Man”
found in 1993 has to be kept
permanently in glacial-like
conditions.
• Reconstruction is like building a three-dimensional
puzzle where you’re not sure which pieces belong and you
know not all of the pieces are there.
• First, archaeologists typically examine the form or shape of an
artifact.
• For most common artifacts, such as ceramics, forms are known well
enough to be grouped into a typology or set of types, which is the
primary purpose of formal analysis.
• Typology provide a lot of information about the artifact,
including:
• Its age
• Species and culture where it comes from.
• Sometimes, how it was made, used, or
exchanges.
• Reconstruction is like building a three-dimensional
puzzle where you’re not sure which pieces belong and you
know not all of the pieces are there.
• Second, archaeologists often measure artifacts, recording their
size in various, often strictly defined, dimensions. This is called
metric analysis.
• Third, archaeologists, often attempt to understand how an
artifact was made.
• By examining the materials the
artifact is made from and how that
material was manipulated,
archaeologists can learn about the
technology, economy, and exchange
system of the people who made the
artifact.
• Reconstruction is like building a three-dimensional
puzzle where you’re not sure which pieces belong and you
know not all of the pieces are there.
• Finally, archaeologists attempt to understand how an artifact
was used.
• Knowing how an artifact was used gives the archaeologist a direct
window onto ancient life.
• For stone, bone and wood tools, there is a technique called usewear analysis which can
determine how a tool was
used through the careful
examination of the kind of
wear on its edges.
• Knowing how an artifact was made allows the archaeologists to
understand the technology and technical abilities of people in
the past. For example: Thomas Wynn analyzed both the final
forms and the methods used by early humans – Homo erectus
– to make stone tools roughly 300,000 years ago. He found
that manufacturing these tools was a multistage process,
involving several distinct steps and several distinct stoneworking techniques to arrive at the finished product. He then
took his information and evaluated it in term of measure of
human cognitive ability developed by Jean Piaget, and
concluded that the people who made these tools probably had
organizational abilities similar to those of modern humans.
• Knowing how an artifact was
used allows the archaeologists
to know something of people’s
behavior and activities.
Lawrence Keeley conducted
detailed use-wear analyses on
Acheulian hand axes made by
Homo erectus peoples and
found that they had a variety of
uses.
• Some cut meat.
• Others for wood
• To dig in the group (probably for
edible roots).
• Therefore hand axes appear to have
been multipurpose tools for our Homo
erectus ancestors – something like a
Swiss Army knife.
• Ecofacts are diverse, and
what archaeologists and
paleoanthropologists can
learn from them is highly
diverse as well.
• Paleontologists (studying
humans or other species)
can tell a great deal about
an extinct animal from its
fossilized bones or teeth,
but that knowledge is based
on much more than just the
fossil record itself.
• Paleontologists rely on comparative anatomy to help
reconstruct missing skeletal pieces
• New techniques, such as electron microscopy, CAT scans
and computer provide much information about how the
organism may have moved about.
• Chemical analysis of fossilized can suggest what the
animal typically ate.
• Paleontologists are also interested in the surroundings of
the fossil finds
• Much of the evidence for primate evolution comes from
teeth, which are the most common animal parts (along
with jaws) to be preserved as fossils.
• Animals vary in dentition – the number and kinds of
teeth they have, their size, and their arrangement in the
mouth.
• Dentition provides clues to evolutionary relationships
because animals with similar evolutionary histories often
have similar teeth.
• For example, no primates, living or extinct, has more than two
incisors in each quarter of the jaw. That feature, along with
others, distinguishes
the primates from
earlier mammals,
which had three
incisors in each
quarter.
• Dentition also suggests the relative size of an animal and
often offer clues about its diet.
• For example, comparison of living primates suggested that
fruit0eaters have flattened, rounded tooth cusps, unlike leafand insect- eaters, which have more pointed cusps.
• Paleontologists can tell
much about an animal’s
posture and locomotion
from fragments of its
skeleton.
• Arboreal quadrupeds have
front and back limbs of about
the same length; because
their limbs tend to be short,
their center of gravity is close
to the branches on which they
move. They also tend to have
long grasping fingers and
toes.
• Paleontologists can tell much about an animal’s posture
and locomotion from fragments of its skeleton.
• Terrestrial quadrupeds are more adapted for speed so they
have longer limbs and shorter fingers and toes.
Disproportionate limbs are more characteristics of vertical
clingers and leapers and brachiators (species that swing
through the branches).
• Vertical clingers and leapers
have longer, more powerful
hind limbs, branchiators
have longer forelimbs.
• Because we cannot remove features to the lab, we cannot
subject them to the same range of analyses as artifacts,
ecofacts, and fossils.
• Archaeologists developed a number of powerful tools to
analyze features in the field.
• The primary one is detailed mapping, usually using a surveyor’s
transit.
• Geographic information system
(GIS) allow the archaeologist to
produce a map of the features
on a site and combine that map
with information about other
archaeological materials found
there.
• Archaeologists do not study fossils and artifacts as
individual objects.
• They put all the materials discovered in one site in
context. This means how and why are the artifacts and
other materials are related – This is what archaeology is
all about.
• Fossils and artifacts maybe beautiful or interesting by
themselves, but it is only when
they are placed in context with
the other materials found on a
site that we are able to “read”
and tell the story of the past.
• An important part of putting artifacts and other materials
into context is putting them in chronological order
• Dating methods include:
• Relative dating is used to determine the age of a specimen.
• Absolute dating or chronometric dating is used to measure how
old a specimen or deposit is in years.
• Stratigraphy
• The study of how different rock and
solid formations are laid down in
successive layers or strata.
• Oldest layers are generally deeper or
lower than more recent layers.
• The earliest, and still the most
common used.
• Indicator artifacts or ecofacts are
used to establish a stratigraphic
sequence.
• If a site has been disturbed,
stratigraphy will not be a satisfactory
way to determine relative age.
• Many of the absolute dating methods are based on the decay of
a radioactive isotope. Because the rate of decay is known, the
age of the specimen can be estimated, within a range of
possible error.
• Radiocarbon Dating or Carbon 14 dating
• The most popular known methods of determining the absolute age
of a specimen.
• All living matter possesses a certain amount of radioactive form of
carbon (Carbon 14). After an organism
dies, it no longer takes in any of the
radioactive carbon. Carbon-14 decays
at a slow but steady pace and reverts
to nitrogen-14. The rate at which carbon
decays –its half life – is known: C-14
has a half life of 5,730 years
• Thermoluminescence Dating
• Many minerals emit light when they
are heated.
• This cold light comes from the release,
under heat, of “outside” electrons
trapped in the crystal structure.
• Thermoluminescence dating makes
use of the principle that if an object is
heated at some point to a high
temperature it will release all the
trapped electrons it held previously.
The amount of Thermoluminescence
emitted when the object is tested
during testing allows researchers to
calculate the age of the object.
• Thermoluminescence dating is well
suited to sample of ancient pottery,
brick, tile, and other objects that are
made at high temperatures.
• Electron Spin Resonance
Dating
• Measures trapped electrons
then expose them to magnetic
fields.
• Paleomagnetic Dating
• When rock of any kind form, it
records the ancient magnetic
field of the earth. Since the
earth’s magnetic field has
reversed itself many times, the
geomagnetic patterns in rocks
can be used to date the fossils
within the rocks.
• Potassium-Argon Dating
• Potassium-40 decays at an established rate and forms argon40. The half-life of K-40 is a known quantity, so the age of a
material containing potassium can be measured by the amount
of K-40 c0mpared with the amount of Ar-40. Potassium-Argon
Dating us used to date samples from 5,000 years up t0 3 billion
years old
• Uranium-Series Dating
• The decay of two kinds of
uranium U-235 and U-238
into other isotopes.
• Used especially in caves
where stalagmites and
other calcite formations
form, because water
usually contains uranium
but not thorium.
• Fission-Track Dating
• It entails counting the
number of paths or tracks
etched in the sample by the
fission-explosive divisionof uranium atoms as they
disintegrate.
• One goal is the description or reconstruction of what happened in the
past.
• Archaeologists attempt to determine how people lived in a
particular place at a particular time, and when and how their
lifestyle chance
• Another goal is testing specific explanations about human evolution
and behavior.
• Understand general trends and patterns in human biological and
cultural evolution.
• Archaeology does not simply describe past cultures. It
can also have a profound effect on living people.
• For example, many people find the idea of archaeologists
excavating, cleaning, and preserving the remains of ancestors
to be offensive. Therefore, archaeologists must be sensitive to
the desires and beliefs of the populations that descend from the
ones they are researching.
• Artifacts from some ancient cultures are in great demand by art and
antiquities collectors, and archaeological digs can lead to
uncontrolled looting if archaeologists are not careful about how and
to whom they report their discoveries.
• Archeologists must report all their findings to the public. Since by
excavating a site, they damage it, they must document everything for
future archaeologists who are excavating the same site.