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Introduction
The methods used by archaeologists to gather data
can be applied to any time period, including the very
recent past. One archaeologist in the U.S. has become
known for his study of the garbage discarded by the
people of Tuscon, Arizona in the 1970s! This “garbology”
project proved that even recent artifacts can reveal
a lot about the people who used and discarded them.
Over the past 150 years archaeologists have developed
many effective methods and techniques for studying the
past. Archaeologists also rely upon methods from other
fields such as history, botany, geology, and soil science.
In this section of Methods of Gathering Data you will
learn how archaeologists gather and analyze information
by utilizing historical research techniques, field methods
for data recovery, and laboratory analyses.
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Historical Research Techniques
Every archaeology project begins with a research design
–a plan that describes why the archaeology is
being done, what research questions it hopes to answer,
and the methods and techniques that will be used to
gather and analyze the artifacts and other archaeological
materials. It will also outline where artifacts recovered
from the project will be stored, and how the research
will be reported and shared with the public.
Archival research
Archival research is often the first step in archaeology.
This research uncovers the written records associated
with the study area. If the area was inhabited during
historical times (in the past several hundred years
in North America) the archaeologist will look for primary
historical documents associated with the study area.
This archival research may take the archaeologist to
public or university libraries, the local historical
society or courthouse—or even into people’s
homes! Primary historical documents that archaeologists
may consult before beginning their field research include:
maps and/or photographs of the area, newspapers, land
and tax records, and diaries and letters. Open this
History
Toolkit to learn more about investigating the past
with primary sources.
In addition to primary historical documents, archaeologists
will look for site reports that have been prepared by
other archaeologists who have studied this area. These
reports will describe what was found in this area during
any previous archaeological investigations and will
help guide the new research. Documentation files for
all of the recorded prehistoric and historic sites in
each state are maintained in the State Historic Preservation
Office, along with archaeological research reports pertaining
to sites in the state.
Oral History
Oral history is another research method that archaeologists
and historians may use to gather information. It includes
any kind of information passed down by word of mouth,
like stories you have been told about your family history,
as well as traditions that your family observes. Archaeologists
today collaborate with descendants of Native American
peoples, and with African American communities who are
only a few generations removed from the lives of their
enslaved or free ancestors, to better understand the
cultural traditions of their pasts. Archaeologists working
on the 19th century Levi Jordan Plantation in Texas
have interviewed descendants of both the plantation
owners and the enslaved plantation workers as part of
their research. These archaeologists hope to include
the “voices’ and perspectives of all of
the past peoples who lived and worked on this plantation
into their research. They have created the Levi
Jordan web site
to share this information with the public and to allow
the public to communicate with the archaeologists.
At Castle Rock Pueblo in southwestern Colorado archaeologists
have learned about the past culture of the Anasazi peoples
through both the objects left behind, and the oral traditions
of modern Puebloan people. Now get ready to take an
electronic field trip back in time to Castle
Rock Pueblo in AD 1200 and solve a mystery while
you are there.
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In the Field
While historians and archaeologists both use written
documents to learn about the past, only archaeologists
are trained to find and interpret archaeological sites.
Here you will learn about some of the field methods
archaeologists use to find sites and, when necessary,
to excavate them.
Tools of the Trade
You may think of shovels when you think of digging,
but the most important piece of equipment in the archaeologist’s
toolkit is actually the trowel. A trowel is used to
carefully remove thin layers of soil from test units.
Of course, many other tools are used by archaeologists
in the field and lab to dig, sift, measure, and analyze
artifacts. View some of these computer
animations of tools and equipment that archaeologists
use. Some, like the Scanning Electron Microscope (SEM)
are very specialized and high tech. Others, like tape
measurers, toothbrushes, brooms and dustpans, are household
objects! You can also view photographs
of archaeologists using some of these tools on sites.
How Do You Find Sites?
Archaeologists use a number of different methods to
find sites—and sometimes they are found just by
accident! The prehistoric burials at Low
Hauxley on the coast of England were discovered
by an observant beach walker who noticed a stone box
sticking out of a sand dune after a storm. A burial
ground with remains of more than 400 17th and 18th century
Africans was discovered during building construction
in New York City. The
African Burial Ground was made a National Monument
because of its importance and significance.
An archaeological predictive model is a tool that
indicates the probability that an archaeological site
will occur in a certain area. It helps determine where
you look for sites based on factors like distance from
water, ground steepness, soil type, and other factors
that influence where people settle or perform certain
tasks. The methods used to find sites will depend upon
the kind of research questions that the archaeologist
is trying to answer. If highway or housing construction
is planned, archaeologists may need to know of any archaeological
sites on the property. First they will check if any
previous surveys have been done in the area and, if
so, what was found. If no previous sites have been recorded,
the archaeologist will conduct an archaeological survey
to determine if the area contains any sites.
If sites are found, the archaeologist will want to
know how many, their location, and how the sites relate
to each other. Usually, to save time and money, only
a sample of the area is tested.
Surface Surveys
A surface survey is a systematic examination of the
land. A team of archaeologists will walk in straight
lines back and forth across the study area looking for
evidence of past human activity, including stone walls
or foundations; artifacts made of stone, ceramics, or
metal; color changes in the soil that may indicate features
such as hearths, middens (garbage pits), or storage
pits They will use a compass and long tape measure to
make sure they walk in a straight line and will record
the exact location of all evidence they find. Artifacts
are collected and put in bags with a label of their
exact location. Features, which cannot be removed, are
photographed and drawn. This technique is useful in
plowed fields.
Shovel Test Pits
Shovel test pits (or “STP’s”) are
a series of shallow pits dug in an area that archaeologists
believe to be a potential site, revealing artifacts
or features. Usually test pits are done where the ground
has not been farmed or plowed and it contains a lot
of surface vegetation. The soil may be screened (sifted)
to recover small artifacts and often profiles (pictures)
of the test pits are drawn to record what the soil looks
like in each unit.
Geophysical Surveys
There are a number of non-invasive techniques archaeologists
can use to find sites without having to dig. Examples
of geophysical surveys that do not involve disturbing
the soil include are magnetometry,
resistivity
and ground
penetrating radar or GPR.
Evaluating Site Significance
After conducting a survey an archaeologist will have
enough information to determine if any significant archaeological
resources are located in the study area. If no sites
are found, or if the sites are not determined to be
“significant” as defined by the law in the National
Historic Preservation Act then construction may
proceed. The archaeologist will write and file a site
report in the State Historic Preservation Office, which
describes their research. If significant sites were
found, an excavation may be planned. In the next section
we will discuss how important data is recovered from
archaeological sites through excavation.
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Data Recovery
Believe it or not archaeologists do not often excavate
(dig) entire sites! Archaeology is a destructive science—meaning
that once a site is excavated it is gone forever. The
artifacts and information gathered remain, but the site
itself can never be recreated. Excavating sites is also
costly and time consuming. Once the dig is done, archaeologists
have a professional responsibility to analyze all of
the artifacts and information obtained, to report on
their research in scholarly journals and to the public,
and to curate the collections. For all of these reasons,
archaeologists generally excavate sites only when they
are threatened by destruction from construction or development
or when they may reveal important information about
past cultures. And they usually excavate only a small
portion of any site.
Although archaeologists work on all kinds of sites
and in all parts of the world, the same basic process
is followed everywhere when an excavation is planned.
Research Design
Before an excavation begins, archaeologists write
a research design. This outlines “who, what, where,
when, how, and why ” the fieldwork is being carried
out. This important document is reviewed before archaeologists
are granted permission to excavate a site. In the U.S.
this plan must be reviewed by the State Historic Preservation
Office (SHPO) where the work will be carried out. If
an American archaeologist wants to work in a foreign
country, permission must be granted by the appropriate
agency in that government. Tribal (Indian) lands in
the U.S. have their own review processes and some tribes
have their own archaeology programs that control access
to sites on tribal lands. Once a research design is
approved and permits area granted, a team is put together
and the necessary tools and materials are gathered.
Gridding the Site
Once a site has been excavated, it is gone forever.
Because of this, archaeologists must record exactly
where all of the artifacts and features on a site are
located. Before any soil or artifacts are removed from
a site, a site grid is created. A datum point, or fixed
reference point from which all measurements are taken,
is established and a rectangular grid is superimposed
over the whole site. Each square in the grid is precisely
measured and assigned a number. These squares are often
referred to as units. This system allows the archaeologist
to create a precise map of the site and to record the
exact location of all the features and artifacts on
the site.
Excavating a Unit
Archaeologists use a statistical sampling method to
select which squares or units they will excavate. To
begin they will collect surface artifacts, then remove
any ground cover using a shovel and trowel. All soil
removed from a unit is screened (sifted) to recover
small artifacts and ecofacts whose exact location, both
horizontally and vertically, is recorded. Artifacts
from each unit are stored in plastic bags that are labeled
with the site and excavation unit numbers and level.
The unit may be dug in arbitrary levels (such as every
10 cm) or by following the natural stratigraphy (layers)
of the unit. These
short video clips show how to prepare a test unit
for excavation. Phil Harding--of the popular British
archaeology series “The Time Team”-- demonstrates
the proper way to use a trowel to remove soil from a
unit.
Stratigraphy
Over time both natural processes like the decay of organic matter, and cultural (caused by humans) processes, create soil layers. In cross section these soil layers resemble a layer cake, with the oldest layers on the bottom and the most recent layers on the top. This is called the Law of Superposition and is one of the most important principles in archaeology. Stratigraphy is the study of geological or soil layers that is used to determine the relative age of each layer. There are many factors that can disturb the stratigraphy on a site and make it hard to determine the relative ages of the layers. Look at how 4,000 years of natural and cultural processes can combine to create and disturb the stratigraphy on an archaeological site. Stratigraphy is one clue used by archaeologists to determine the relative age of an artifact or site. In the next section we will look t other ways of determining how old something is.
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In the Lab
Archaeologists spend much more of their time in the
laboratory analyzing artifacts and data than they do
in the field. In this section, you will learn how archaeologists
analyze artifacts, features, and other information recovered
in the field to help answer their research questions.
During the investigative process, they also seek to
learn when site was occupied, the purpose of the objects
recovered, what the people ate, the kinds of structures
they lived and worked in, with whom they traded, and
much more. They may also look at how the site they are
analyzing relates to other sites that are nearby or
quite distant. The analysis will depend upon what research
question the archaeologist began the project with.
“How old is it?”
There are a variety of techniques that can be used to find out how old an artifact or an archaeological site is. Stratigraphy can determine the relative age of soil layers and artifacts and can help us understand the order in which events occurred. However if an artifact of known age such as a coin with a mint date is found in a soil layer it can tell us when something occurred. Tree-ring dating, or dendrochronology is one of the oldest dating methods used by archaeologists. It is based on the principle that trees produce growth rings each year and the size of the rings will vary depending upon rainfall received each year. Archaeologists have built up long sequences of rings from tree trunks that extend back centuries. In the American Southwest tree ring dating goes back to 59 BC. Radiocarbon (C14) dating is the most widely used method to date objects made of organic matter. Potassium-argon dating can be used to date extremely old – up to 100,000 years old. Obsidian hydration dating is used on artifacts made from volcanic glass. This is just a sample of the many physical and chemical dating methods that archaeologists have used to date archaeological sites.
Analyzing Artifacts
Artifacts are important sources of information for
archaeologists. Artifacts can tell us about the diet,
tools, weapons, dress, and living structures of people
who made and used them. Recovered artifacts are washed,
sorted and catalogued, and stored after they are brought
back from the field. Archaeologists analyze individual
artifacts but also may sort them into groups to see
patterns. For example, they might weigh all of the oyster
shells together or count all of the nails and consider
them as one unit. Where artifacts are found on the site
provides a clue to the kinds of activities that occurred
such as stone tool or weapon production or food preparation.
The type of material the artifact is made of is another
important piece of information that can inform whether
the materials were obtained locally or by trading with
another group. Artifacts provide a window into the lives
of peoples who lived before.
Analyzing Features
A feature shows human activity but unlike most artifacts
it cannot be removed from the archaeological site. A
feature might be a stain in the soil that is evidence
of a former fence post. Photographs, drawings, and soil
samples of the fence post collected by the archaeologist
are part of the scientific record of that feature and
are just as important as the nails and other artifacts
that might be found nearby. Features like soil stains
can reveal the outlines of prehistoric or historic structures
such as houses and barns, or longhouses and earthen
lodges. Other types of features include hearths (fire
pits), storage pits, and middens –what archaeologists
call garbage dumps! Privies (outhouses) are important
features in historical archaeology sites because people
used to dump their garbage as well as broken pottery
and other housewares into them.
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Resources
Historical Research Techniques
In the Field
Data Recovery
- Gridding
An Archaeological Site
In this activity students establish a grid over an
archaeologialsite and determine the location of artifacts
within each grid.
- What’s in the Soil?
Students cut out and identify illustrations of artifacts, and paste them into layers of soil to illustrate the stratigraphy found on an archaeological site.
How Old Is It?
Analyzing Artifacts
Analyzing Features
Click here for more Lesson Plans and Activities
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