The International History Project

Archeology is the scientific study of past human culture and behavior, from the origins of humans to the present. Archaeology studies past human behavior through the examination of material remains of previous human societies. These remains include the fossils (preserved bones) of humans, food remains, the ruins of buildings, and human artifacts—items such as tools, pottery, and jewelry. From their studies, archaeologists attempt to reconstruct past ways of life. Archaeology is an important field of anthropology, which is the broad study of human culture and biology. Archaeologists concentrate their studies on past societies and changes in those societies over extremely long periods of time.

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With its focus on the ancient past, archaeology somewhat resembles paleontology—the study of fossils of long-extinct animals, such as dinosaurs. However, archaeology is distinct from paleontology and studies only past human life. Archaeology also examines many of the same topics explored by historians. But unlike history—the study of written records such as government archives, personal correspondence, and business documents—most of the information gathered in archaeology comes from the study of objects lying on or under the ground 

Archaeologists refer to the vast store of information about the human past as the archaeological record. The archeological record encompasses every area of the world that has ever been occupied by humans, as well as all of the material remains contained in those areas. Archaeologists study the archaeological record through field surveys and excavations and through the laboratory study of collected materials.

Many of the objects left behind by past human societies are not present in the archaeological record because they have disintegrated over time. The material remains that still exist after hundreds, thousands, or millions of years have survived because of favorable preservation conditions in the soil or atmosphere. For the most part, the only things that survive are durable items such as potsherds (small fragments of pottery), tools or buildings of stone, bones, and teeth (which survive because they are covered with hard enamel). Because many items disintegrate over time, archaeologists get an incomplete view of the past that they must fill in with other kinds of information and educated reasoning. On rare occasions, however, delicate objects have been preserved. For example, fabrics and flowers were found in the celebrated tomb of Tutankhamun, an Egyptian pharaoh who was buried in 1323 BC.

Archaeology became established as a formal discipline in the 19th and early 20th centuries. At that time, most archaeological work was confined to Europe, to the so-called cradle of civilization in southwestern Asia, and to a few areas of the Americas. Today, archaeologists study the great cultural diversity of humanity in every corner of the world.

Archaeological study covers an extremely long span of time and a great variety of subjects. The earliest subjects of archaeological study date from the origins of humanity. These include fossil remains believed to be of human ancestors who lived 3.5 million to 4.5 million years ago. The earliest archaeological sites include those at Hadar, Ethiopia; Olduvai Gorge and Laetoli, Tanzania; East Turkana, Kenya; and elsewhere in East Africa. These sites contain evidence of the first appearance of bipedal (upright walking), apelike early humans. Laetoli even reveals footprints of humans from 3.6 million years ago. Some sites also contain evidence of the earliest use of simple tools. Archaeologists have also recorded how primitive forms of humans spread out of Africa into Asia about 1.8 million years ago, then into Europe about 900,000 years ago.

The first physically modern humans, Homo sapiens sapiens, appeared in tropical Africa between 200,000 and 150,000 years ago—dates determined by molecular biologists and archaeologists working together. Dozens of archaeological sites throughout Asia and Europe show how people migrated from Africa and settled these two continents during the last Ice Age (100,000 to 15,000 years ago). Archaeological studies have also provided much information about the people who first arrived in the Americas over 12,000 years ago.

Archaeologists have documented that the development of agriculture took place about 10,000 years ago. Early domestication—the planting and harvesting of plants and the breeding and herding of animals—is evident in such places as the ancient settlement of Jericho in Jordan and in Tehuacán Valley in Mexico. Archaeology plays a major role in the study of early civilizations, such as those of the Sumerians of Mesopotamia, who built the city of Ur, and the ancient Egyptians, who are famous for the pyramids near the city of Giza and the royal sepulchers (tombs) of the Valley of the Kings at Thebes. Other sites that represent great human achievement are as varied as the cliff dwellings of the ancient Anasazi (a group of early Native Americans) at Mesa Verde, Colorado (see Mesa Verde National Park); the Inca city of Machu Picchu high in the Andes Mountains of Peru; and the mysterious, massive stone portrait heads of remote Easter Island in the Pacific.

Archaeological research spans the entire development of phenomena that are unique to humans. For instance, archaeology tells the story of when people learned to bury their dead and developed beliefs in an afterlife. Sites containing signs of the first simple but purposeful burials in graves date to as early as 40,000 years ago in Europe and Southwest Asia. By the time people lived in civilizations, burials and funeral ceremonies had become extremely important and elaborate rituals. For example, the Moche lords of Sipán in coastal Peru were buried in about AD 400 in fine cotton dress and with exquisite ornaments of bead, gold, and silver. Few burials rival their lavish sepulchers. Being able to trace the development of such rituals over thousands of years has added to our understanding of the development of human intellect and spirit.

Archaeology also examines more recent historical periods. Some archaeologists work with historians to study American colonial life, for example. They have learned such diverse information as how the earliest colonial settlers in Jamestown, Virginia, traded glass beads for food with native Algonquian peoples; how the lives of slaves on plantations reflected their roots in Africa; and how the first major cities in the United States developed. One research project involves the study of garbage in present-day cities across the United States. This garbage is the modern equivalent of the remains found in the archaeological record. In the future, archaeologists will continue to move into new realms of study.

Archaeology covers such an enormous span of time that archaeologists specialize in different time periods and different cultures. They also specialize in particular methods of study. Some archaeologists study human biological and cultural evolution up to the emergence of modern humans. Others focus on more recent periods of major cultural development, such as the rise of civilizations. Some study only the ancient or classical civilizations of the Middle East or Europe. Others research later historical subjects and time periods, using both written and archaeological evidence. Many archaeologists have expertise in other fields that are important to archaeological study, including physical anthropology (the study of human biology and anatomy), geology, ecology, and climatology (the science of weather patterns).

Prehistoric archaeology is practiced by archaeologists known as prehistorians and deals with ancient cultures that did not have writing of any kind. Prehistory, a term coined by 19th-century French scholars, covers past human life from its origins up to the advent of written records. History—that is, the human past documented in some form of writing—began 5000 years ago in parts of southwestern Asia and as recently as the late 19th century AD in central Africa and parts of the Americas. Because there are no written records for prehistory, prehistorians rely entirely on material remains for evidence.

Discoveries of early human ancestors have changed the way many people think about what it means to be human. For instance, researchers working in southern Ethiopia and northern Kenya have found evidence that some human ancestors who lived about 2 million years ago were scavengers. They used stone tools to butcher game taken from the kills of predators such as lions. In 1978 at Laetoli, Tanzania, paleoanthropologist Mary Leakey discovered a fascinating early human site: sets of hominid footprints left in now-hardened volcanic ash. This find provides some of the strongest evidence that hominids walked upright as early as 3.6 million years ago.

Some prehistorians specialize in studying various periods of the Stone Age. This period of human cultural development began about 2.5 million years ago, when humans learned to make simple stone tools. The Stone Age ended at different times in different parts of the world, roughly within the last 10,000 years.

Important Stone Age archaeological sites include the 30,000-year-old rock paintings of the Grotte de Chauvet cave in southeastern France (see Paleolithic Art) and Syria’s 10,000-year-old Abu Hureyra farming village in the Euphrates Valley. By analyzing plant remains at Abu Hureyra in the 1970s and 1980s, British archaeologist and botanist Gordon Hillman showed that the inhabitants of this village were among the earliest people to cultivate wild cereal grasses, ones that evolved into what we know today as wheat and barley.

At their height, ancient civilizations centered on magnificent cities with large buildings and tombs. Some of these cities also had roads and human-made waterways. Archaeologists who study this period of the human past investigate how sufficient political and economic power developed to create and maintain early civilizations, and what factors led to the decline of such large and powerful societies.

Archaeologists who study ancient civilizations also often concentrate on particular regions. Egyptologists, for instance, study the civilization of ancient Egypt. Generations of Egyptologists have studied the numerous finds from the well-preserved tomb of the pharaoh Tutankhamun. This tomb is located in the Valley of the Kings at Thebes and was found by British archaeologist Howard Carter in 1922. Other archaeologists have recorded architectural details, paintings, and inscriptions from the many other tombs in the Valley of the Kings. These works are in danger of eroding in Egypt’s harsh desert environment. Egyptological research projects also study numerous other important sites along the Nile River valley—including the city of Memphis and the Old Kingdom mortuary complex of Giza—as well as north to the Mediterranean Sea, east to the Sinai Peninsula, and south into the Nubian Desert.

Classical archaeology examines ancient Greek and Roman civilization. During the late 1800s German-born American archaeologist Heinrich Schliemann conducted expeditions in Greece and Turkey, near the coasts of the Aegean Sea. Schliemann first excavated in Hissarlik, Turkey, revealing what he claimed were several distinct periods of the great city of Troy, which is described in the Iliad, an epic tale by Homer. Schliemann also excavated in Mycenae, Greece, searching for the tomb of the Greek leader Agamemnon, who campaigned against Troy in the Trojan War. Schliemann conducted quick excavations, destroyed large portions of his sites, which earned him the suspicion and anger of the Turkish government.

Many other archaeologists followed Schliemann, conducting more methodical and scientific excavations of lands surrounding the Aegean. Recent archaeology of the classic civilizations of Europe has concentrated on the lives of common citizens. American archaeologist David Soren, for example, led a research team in the 1980s in southwestern Cyprus. Soren and his team reconstructed the events of a powerful earthquake that struck the Roman port of Kourion in AD 365. Soren’s team uncovered collapsed buildings in which entire families had been buried in their sleep.

Historical archaeology examines past cultures that used some form of writing. Although writing was invented thousands of years ago in some parts of the world, many historical archaeologists study only the past few hundred years. Historical archaeologists use written documents as part of their research, and they may work in collaboration with historians. This kind of archaeology first developed in North America and England. It continues to thrive in both of those places but is also practiced in many other parts of the world. Historical archaeologists have studied a wide variety of subjects, such as relations among settlers and Native Americans in colonial North America, Spanish religious missions in the southern United States, medieval villages in England, and early factories of the Industrial Revolution in Europe and North America.

Underwater archaeology uses special methods to study shipwrecks and other archaeological sites that lie beneath water. Archaeologists who work under water rely on sophisticated diving and excavating equipment and employ special techniques to preserve perishable materials that have been submerged for long periods. In an extensive underwater archaeological project from 1983 to 1994, a team led by American archaeologist George Bass and Turkish archaeologist Cemal Pulak recovered the cargo of a heavily laden Bronze Age ship at Uluburun, off the southern coast of Turkey. The ship, which was wrecked in a storm around 131O BC, carried enough copper and tin ingots to forge weapons for a military regiment of several hundred people.

Some archaeologists learn skills from other disciplines to form specialized fields of study. For instance, experts in zooarchaeology study animal bones found in and around human habitations, from which much can be learned about human subsistence methods. Archaeologists who specialize in paleoethnobotany study the plants used by ancient people for food, medicine, and other purposes. Some archaeologists also have expertise in such subjects as radiocarbon dating methods or the techniques used in ancient metallurgy (the making of metals from mineral ores).

Another archaeological specialty, geoarchaeology, determines what ancient environments and landscapes were like. Geoarchaeologists use many sources of information and specialized techniques to learn about environmental conditions of the past. For example, they learn about past global and regional temperature changes by examining changes in the composition of the air, water, and sediments in large cores of the earth taken from the deep-sea bottom or the polar ice caps.

Some geoarchaeologists also have expertise in zooarchaeology or paleoethnobotany. They may use this expertise to examine millions of tiny fossil pollen grains preserved in old layers of sediment. By noting the differences in the fossils, geoarchaeologists can chart how the earth’s vegetation changed over time.

The bones of some animals, including rodents and many invertebrates, can also provide clues about ancient climates. For example, in the 1950s and 1960s American archaeologist Hallam Movius gathered such data from the Abri Pataud rockshelter of the late Ice Age in the Dordogne Valley of southwestern France. His research showed how hunter-gatherer bands living there 18,000 years ago adapted to constantly changing climatic conditions, which alternated between bitter cold and warmer periods.

Archaeologists working with botanists have also learned about prolonged drought cycles that affected the Anasazi Pueblo peoples of the North American Southwest. Because of the effects of such drought cycles on food production, these peoples abandoned large towns and dispersed into small villages about 700 years ago. Since the 1960s, American tree-ring expert Jeffrey Dean has examined wooden beams from ancient pueblos (dense villages of adobe and stone houses). Dean has used dendochronology (the study of annual growth ring sequences in tree trunks) to determine when droughts occurred and how long they lasted.

Modern archaeological studies have three major goals: (1) chronology, (2) reconstruction, and (3) explanation. Chronologies establish the age of excavated materials. Reconstructions are models of what past human campsites, settlements, or cities—and their environments—might have looked like, and how they might have functioned. Explanations are scientific theories about what people living in the past thought and did.

Archaeologists carefully record their excavations in a way that allows them to piece together culture histories—chronologies (time perspectives)of past cultures. Excavations reveal the order in which remains were deposited, while laboratory analyses can give the actual age of remains. Archaeologists also document how each artifact or fossil lies in the ground in relation to other artifacts or fossils. This task involves careful recording of geological and artifact layers, or strata.

Chronological data can provide information such as how the use of a new style of pottery or type of weapon spread from one region to another over time. By analyzing this information for several related archaeological sites, archaeologists assemble long sequences of past human cultures.

For example, in the 1920s American archaeologist Alfred Kidder created a culture history at Pecos Pueblo, near Santa Fe, New Mexico. Kidder excavated human occupations at the pueblo going back more than 2000 years. (Occupations are clearly defined layers of artifacts and fossils created by people who lived at a site.) He also collected pottery passed down through many generations of pueblo inhabitants. From these collected items, he was able to establish a continuous record of pottery styles from 2000 years ago to the 1920s. Kidder then analyzed trends and changes in pottery styles through time. He associated each stylistic change in pottery with a change in the people’s culture, just as people today associate changes in clothing styles, for example, with changes in the culture. Archaeologists have since used the Pecos pottery sequence to assign approximate dates to dozens of sites throughout the Southwest and to determine cultural ties and differences among them.

Building on information about the chronology and composition of sites and their environments, archaeologists reconstruct how life might have looked in particular places at particular times. The reconstruction of past ways of life depends on interpretation of well-documented material remains and environmental remains in their chronological contexts. Environmental remains may include animal body parts—such as bones, skins, and feathers—as well as parts of plants, such as seeds, pollens, and spores.

In the 1960s American archaeologist Richard MacNeish and a group of archaeologists and scientists from other fields reconstructed the subsistence patterns (ways of obtaining and producing food) of people who once lived in Mexico’s Tehuacán Valley. In the 1980s teams of later researchers refined MacNeish’s reconstructions. These researchers analyzed the chemical composition of materials from MacNeish’s studies and newly collected samples, including human bones and plant and animal remains found near those bones. The analyses revealed a shift in subsistence patterns over a 9000-year period. During this time, the inhabitants of the valley shifted from a pattern of seasonal migration and a diet of wild plants and game animals to a more stable pattern of settlement and a diet based on cultivated maize (corn), beans, and squash.

In another classic study of an archaeological site in its ecological setting, British archaeologist Grahame Clark excavated a tiny Stone Age hunting site in 1949. The site at Star Carr in northeastern England dated as far back as 10,700 years ago. By analyzing animal bones and tiny pollen grains, Clark determined that the site was at one time set amid reeds at the edge of a glacial lake and had been surrounded by a dense birch forest. The site yielded a wide variety of tools made of stone, bone, and antler. In the 1980s and 1990s archaeologists have returned to the site with more refined methods of analysis. They have been able to reconstruct the details of a yearly springtime habitation of the site over many centuries.

Archaeologists commonly use theoretical models, experiments, and observations of the world as it is today to try to explain what happened in the past. They have attempted to explain, for example, why people first began to walk upright and why civilizations that once flourished suddenly collapsed. Good explanations come from well-thought-out theoretical models that propose ways in which the existing archaeological record might have been formed. Explanations can include factors such as environmental changes, demographic shifts (changes in population makeup and size), migrations, and patterns of thought and behavior. Whereas reconstructions use physical remains to create a picture of the past, explanations are attempts to answer questions about the past. For instance, the reconstruction of changes in settlement and subsistence patterns of the inhabitants of the Tehuacán Valley does not explain why these changes took place. They might be explained by any one factor or a combination of factors, such as a dramatic change in weather patterns, an increase in the population, or a conscious decision to take advantage of a new discovery—agriculture. To be persuasive, an explanation has to fit with the existing archaeological data and stand up to scrutiny over time.

It would be extremely difficult for archaeologists to interpret the archaeological record if they thought that people and cultures of the past bore no resemblance to those of today. Because they assume that there has been some continuity through time, archaeologists commonly use information from the present to interpret the past. One way they accomplish this is by doing archaeological research on present-day societies—studying the ways in which people live today and the material traces that their activities leave behind. This method is known as ethnoarchaeology. Archaeologists also try to experimentally recreate the patterns they find in their research—a technique known as experimental archaeology. Successful recreations can become plausible explanations for how the archaeological record was formed.

Artifact and fossil evidence reveals that humans lived by hunting and gathering until relatively recently in human evolution. Archaeologists have tried to understand this way of life by studying living groups of hunter-gatherers, including the Aborigines of Australia, Inuit and other Eskimo peoples of the Arctic, and the San people of Botswana’s Kalahari Desert. Through ethnoarchaeology, archaeologists cautiously deduce characteristics of past cultures based on their observations of living peoples. Archaeologists believe that present-day hunter-gatherers and people who lived throughout much of prehistory share some aspects of their ways of life.

To document the lives of living peoples, archaeologists do a brief type of ethnographic research, the method of study usually practiced by cultural anthropologists. In this method, the archaeologists spend time among the people they are studying, keeping detailed records of the people’s daily activities and behaviors. They also make precise records of the people’s abandoned campsites and settlements, including discarded food remains and artifacts, to compare with patterns they see in archaeological sites. Ethnoarchaeological research can provide valuable clues for deciphering accumulations of artifacts and other remains found in archaeological sites, particularly accumulations that resulted from such activities as toolmaking or animal butchering.

In an ethnoarchaeological study made from 1969 to 1973, American archaeologist Lewis Binford documented the caribou hunting methods of the Nunamiut Eskimo of Alaska. He followed the hunters, studied their butchering techniques, and mapped their kill and butchering sites. Binford collected information that proved extremely useful in interpreting distributions of animal bones in other archaeological sites.

Archaeologists may also try to recreate the artifacts and patterns they find in excavated sites in order to understand how artifacts were made and how patterns formed. In experimental archaeology, archaeologists perform controlled experiments to help interpret finds such as abandoned fire hearths, accumulations of waste from stone toolmaking, and collapsed buildings.

In experiments conducted in the 1980s, American paleoanthropologists Nicholas Toth and Kathy Schick reconstructed the simple stone toolmaking techniques of early humans through controlled replication. They and their research teams used the same types of stones that the first toolmakers used and even collected them from the same areas. They tried making tools in a variety of ways. By making tools using both their right and left hands, and then comparing the resulting patterns in their tools with those from prehistoric sites, Toth and Schick learned that some early humans were left-handed. In addition, the stone flakes left by ancient toolmaking allow an expert to reconstruct minute details of stone technology, such as whether (and even how many times) a tool was retouched to give it a new, sharp edge. Toth and Schick and their research teams also butchered animal carcasses with stone tools to see what the resulting cuts look like. This information has helped archaeologists determine the extent to which ancient peoples hunted or scavenged for meat.

Some of the most ambitious experimental archaeology projects have involved long-term trials with prehistoric farming methods in Europe. Since 1972 archaeologists have experimented with prehistoric agricultural methods at Butser in southern England. Using only ancient tilling implements, they plant and grow varieties of grains used in prehistoric times. Other research at Butser involves breeding animals that were bred in prehistoric times. Researchers also have experimented with storing food supplies in covered pits in the ground, a practice that was common around 300 BC during the Iron Age. Using this technique, ancient farmers could keep food supplies over long winters and store seed to plant each spring.

Before archaeologists excavate, they locate potential sites and test them to determine if the sites will yield artifacts and other remains. Until about the late 1960s, many archaeologists favored large-scale excavations, arguing that the more ground they cleared the more they would discover. Today, archaeologists know that any disturbance of an archaeological site, however scientific, actually destroys an irreplaceable record of the past. For this reason, modern excavations are usually done on a more limited scale.

Once excavated, archaeological sites are gone forever. Good survey techniques are crucial for minimizing damage to the record and for locating sites that contain objects of interest. Increasingly, archaeologists are also using less intrusive ways of investigating the past. Advanced technologies that can provide archaeological data without digging—such as various kinds of radar, magnetic sensors, and soil electric-resistance detectors—can keep actual excavation to a minimum.

How do archaeologists know where to find what they are looking for when there is nothing visible on the surface of the ground? Typically, they survey and sample (make test excavations on) large areas of terrain to determine where excavation will yield useful information. Surveys and test samples have also become important for understanding the larger landscapes that contain archaeological sites.

Some archaeological sites have always been easily observable—for example, the Parthenon in Athens, Greece; the pyramids of Giza in Egypt; and the megaliths of Stonehenge in southern England. But these sites are exceptions to the norm. Most archaeological sites have been located by means of careful searching, while many others have been discovered by accident. Olduvai Gorge, an early hominid site in Tanzania, was found by a butterfly hunter who literally fell into its deep valley in 1911. Thousands of Aztec artifacts came to light during the digging of the Mexico City subway in the 1970s. In Israel in 1947, two Bedouins discovered the Dead Sea Scrolls by accident in a cave.

Most archaeological sites, however, are discovered by archaeologists who have set out to look for them. Such searches can take years. British archaeologist Howard Carter knew that the tomb of the Egyptian pharaoh Tutankhamun existed from information found in other sites. Carter sifted through rubble in the Valley of the Kings for seven years before he located the tomb in 1922. In the late 1800s British archaeologist Sir Arthur Evans combed antique dealers’ stores in Athens, Greece. He was searching for tiny engraved seals attributed to the ancient Mycenaean culture that dominated Greece from the 1400s to 1200s BC. Evans’s interpretations of these engravings eventually led him to find the Minoan palace at Knossos (Knosós), on the island of Crete, in 1900.

To find their sites, archaeologists today rely heavily on systematic survey methods and a variety of high-technology tools and techniques. Airborne technologies, such as different types of radar and photographic equipment carried by airplanes or spacecraft, allow archaeologists to learn about what lies beneath the ground without digging. Aerial surveys locate general areas of interest or larger buried features, such as ancient buildings or fields.

Ground surveys allow archaeologists to pinpoint the places where digs will be successful. Most ground surveys involve a lot of walking, looking for surface clues such as small fragments of pottery. They often include a certain amount of digging to test for buried materials at selected points across a landscape. Archaeologists also may locate buried remains by using such technologies as ground radar, magnetic-field recording, and metal detectors.

Archaeologists commonly use computers to map sites and the landscapes around sites. Two- and three-dimensional maps are helpful tools in planning excavations, illustrating how sites look, and presenting the results of archaeological research.

Surveys can cover a single large settlement or entire landscapes. Many researchers working around the ancient Maya city of Copán, Honduras, have located hundreds of small rural villages and individual dwellings by using aerial photographs and by making surveys on foot. The resulting settlement maps show how the distribution and density of the rural population around the city changed dramatically between AD 500 and 850, when Copán collapsed. Archaeologists believe the people of Copán may have overfarmed the surrounding land, depleting their primary food supply and forcing them into the countryside in search of fertile land.

American archaeologists René Million and George Cowgill spent years systematically mapping the entire city of Teotihuacán in the Valley of Mexico near what is now Mexico City. At its peak around AD 600, this city was one of the largest human settlements in the world. The researchers mapped not only the city’s vast and ornate ceremonial areas, but also hundreds of simpler apartment complexes where common people lived. Million and Cowgill found evidence in distinctive potsherds that foreign merchants, from areas such as Veracruz on the Gulf of Mexico and the Valley of Oaxaca, lived in small enclaves, apart from the main community of Teotihuacán.

Achaeologists rely on a wide variety of aerial survey methods, all of which are commonly referred to as remote sensing. Remote sensing involves using photography, radar, and other imaging technologies to detect potential sites. The technology was developed largely as a tool for military reconnaissance. During World War I (1914-1918) American military pilots took photographs from the air that revealed previously unknown archaeological sites in France and the Middle East. Archaeologists have used aerial survey techniques ever since.

Aerial photography is especially useful for detecting archaeological sites that are difficult to see from the ground. Aerial photographs reveal human-made geographical features such as earthworks; these giant earthen mounds were erected by prehistoric peoples in many parts of the world, including Britain and North America (Mound Builders). Aerial photos have also revealed entire Roman road systems in northern Africa that are almost invisible from the ground. Some sites appear in aerial photographs as distinctive marks running through agricultural fields and deserts. For instance, at Chaco Canyon, New Mexico, a combination of aerial photographs and other techniques revealed the full extent of an elaborate road system that led to the pueblos and sacred sites of the Anasazi people whose society centered on the canyon between about AD 850 and 1130. The Chaco road system was almost invisible on the ground without the help of air photographs. See also Chaco Culture National Historical Park.

Archaeologists also use other airborne technologies that record information about the earth’s surface and subsurface. Aerial photographs of infrared radiation can detect minute differences in ground temperatures. Using infrared photography, archaeologists identify soils that have been disturbed or manipulated in the past, as well as other ground features that are normally invisible. Infrared photographs and thermal scanners also detect the presence of subsurface stone and variations in soil moisture. Subsurface stone may indicate the presence of buried buildings, and soil moisture differences can reveal ancient crop fields.

Sideways-looking airborne radar (SLAR) is an advanced aerial technology that sends and receives pulses of radiation. These pulses are used to form a detailed picture of the terrain below and around an aircraft’s flight path. SLAR is commonly used for geological mapping and oil exploration; archaeologists find it useful for locating sites under the dense canopy of rainforests.

The excellent imaging capabilities of SLAR helped archaeologists solve the mystery of how the Classical Maya civilization supported its enormous population. This civilization dominated the Yucatán Peninsula region—primarily in what are now Mexico, Belize, and Guatemala—from about the 4th to the 10th century AD. SLAR revealed formerly invisible, gray, crisscrossed grids in the swampy lowlands of the Maya region. Subsequent ground surveys identified these grids as ancient moat-and-field systems, called chinampas, which Maya farmers used to grow large quantities of maize and other staple crops.

Archaeological sites have also been located from space. Imaging radar systems carried on U.S. space shuttle flights in 1981 and 1994 revealed ancient river valleys buried under the sands of the Sahara in northern Africa. American archaeologist C. Vance Haynes discovered 200,000-year-old stone axes in the subsurface deposits of one of these valleys. These tools provide evidence of human habitation in the Sahara when it was a fertile area with plenty of vegetation.

Much archaeological research still takes place on the ground. Most ground surveys involve long days of walking and looking for telltale signs of ancient human habitation. Various objects may remain on the surface for long periods of time. Archaeologists may find pot fragments or stone tools, light-colored ash from ancient fires, and piles of shells accumulated by people who ate shellfish. Other objects come up to the surface when previously built-up sediments are eroded by weather, or they may be brought up by burrowing animals.

The ruins of a few ancient Asian cities—including Jericho in present-day Jordan, Nineveh in present-day Iraq, and Mohenjo-Daro in Pakistan’s Indus Valley—were easily visible above ground at the time of their discovery. Archaeological sites are usually inconspicuous, however.

When an archaeologist has reason to believe that there is something to be found in a particular area, systematic and patient searching sometimes pays rich dividends. British archaeologist Francis Pryor spent many months searching the banks of drainage canals in the flatlands of eastern England. In 1992 he finally found some waterlogged timbers at Flag Fen, a bog near the present-day city of Peterborough. These timbers were the remains of a submerged 3000-year-old Bronze Age settlement and field system. The marshland preserved a long set of posts, the remainder of 50,000 such posts that held up a platform stretching for 1 km (0.6 mi). Beneath the platform Pryor’s excavation team found bones, plant materials, and bronze implements that the inhabitants had thrown into the shallow water, perhaps as religious offerings. Researchers also retrieved the oldest-known wheel in England from the marsh.

Ground-penetrating radar can detect objects and impressions left by decayed remains beneath the earth’s surface. It is a powerful tool for examining buried features at archaeological sites. For instance, in 1989 American archaeologist Payson Sheets used such radar to locate hut floors at the Maya village of Cerén, in what is now El Salvador. The village was buried under volcanic ash in the 6th century AD. Using computers, researchers created a three-dimensional map of the landscape as it appeared before it was buried.

In recent years, many archaeologists have begun to use geographic information systems (GIS) to aid in mapping sites. These computer-based systems allow the collection, storage, and manipulation of environmental, geographic, and geologic data, together with archaeological information, in a single database. Using this technology, archaeologists can create maps that simulate different environments and ways in which people might have used land, living space, and material goods.

Italian archaeologists have used GIS technology to interpret life in the Roman city of Pompeii, which was buried by an eruption of Mount Vesuvius in AD 79. Researchers mapped thousands of computerized pictures of artifacts directly over floor plans of individual houses, matching specific artifacts to the exact locations where they were recovered. Using a database of artifacts, locations, and other information, archaeologists can quickly study a wide variety of interconnected topics about Pompeii, from relationships between people’s wealth and their lifestyles to differences among wall paintings from one dwelling to another.

Many 19th-century archaeological excavations proceeded unscientifically. Archaeologists commonly rushed through disorderly searches for spectacular art works and buried treasure. During the 20th century, archaeologists developed precise, detailed methods of excavation and statistical sampling (mathematical ways of answering questions using relatively small amounts of data). Archaeologists today can often obtain more information from a small trench than they could recover from a large dig a generation ago.

Archaeologists decide where and how much to dig based, in part, on what questions they want to answer; they must also determine the best ways to answer these questions. They must decide, for instance, how much and what types of statistical sampling to use. These choices, as well as time and money limitations, affect archaeologists’ excavation plans. In addition, archaeologists attempt to limit excavations to leave intact as much of the archaeological record as possible. A dig should answer planned research questions while disturbing the archaeological record as little as possible.

Between 1969 and 1988 British archaeologist Barry Cunliffe investigated a 2000-year-old Iron Age Celtic fort built on a hill (for defensive purposes) at Danebury in southern England (see Celts). Cunliffe conducted minimal and careful stratigraphic examination of the hill, observing the layers of earth and the objects contained within the earth. From this information he developed a chronology of the site, establishing what happened there through time. He then conducted a few larger excavations of open areas in the interior of the fort to study the crowded settlement that flourished there. By keeping to his carefully formulated research strategy, Cunliffe left large areas of the site undisturbed for later generations to investigate.

Because of the high costs of excavation and concerns about conserving the archaeological record, most archaeologists today work on small projects in relatively short periods of time. Only rarely do modern-day excavations cover large amounts of land and last many years, as did some earlier digs.

In the early years of scientific archaeology, grand excavations of important sites gave prestige to the archaeologists and institutions that conducted them. British archaeologist Sir Leonard Woolley’s excavation from 1922 to 1934 of the Sumerian city of Ur, in present-day Iraq, typified these expansive and highly publicized digs. Woolley employed hundreds of workers, unearthed entire quarters of the city, and probed to the bottom of the city mound (the accumulation of many generations of inhabitants), the level at which a small farming village had flourished in about 4700 BC. He also excavated a spectacular royal burial site where a buried prince lay entombed. The prince was surrounded by the members of his court, all of whom were executed for the burial.

In contrast, modern excavations can reveal significant amounts of information with a minimum of digging by a small team of people. For instance, in the 1970s and 1980s, American archaeologists Fred Wendorf and Angela Close excavated a series of tiny foraging camps by the Nile River in Egypt. These camps were occupied between about 16,000 and 15,000 BC. The researchers used a combination of wide but shallow excavations and small, narrow test pits to sample the densest concentrations of artifacts, fragments of animal and fish bones, and the remains of hearths. These small-scale excavations allowed the researchers to gain good insights into how foragers lived along the Nile at the end of the last Ice Age.

Archaeological study of large ancient cities and other historical settlements now often involves both scientific excavation and conservation work. For example, at the Maya city of Copán, in present-day Honduras, workers have excavated a temple complex in the city’s center as well as large areas around the center. The excavators have also participated in painstaking reconstruction of collapsed structures. Some buildings contain hieroglyphic accounts of the rulers who ordered their construction. The excavations have provided archaeologists with new information about the ruling dynasties of Copán. The accompanying conservation work has preserved the site for posterity and has created an attraction for tourism, a major part of the Honduran economy.

Archaeological excavation involves meticulous recording of the location of all artifacts, fossils, and other items of interest. How this information will be recorded is established at the beginning of a dig. Researchers commonly use a grid system to record the objects found in a site. A grid system is anchored to a baseline called a datum point. The datum point serves as the center of reference for the location of artifacts, other remains, and features of the terrain. By using such a system, archaeologists can record the precise horizontal position of any find, however small, with reference to other objects in the dig. They also record the precise vertical location of each object, according to the geological and occupation layers in which they are buried.

Using computerized recording equipment and three-dimensional plots, researchers can recreate a site on a computer screen for analysis. Computer-based mapping systems, such as GIS, aid archaeologists in creating precise surveys of major sites and in reconstructing the design of ruined buildings down to intricate architectural features.

The details of excavation methods vary from one site to the next, but the basic principles of careful recording and precise archaeological methods remain the same everywhere—on land or in water, for the excavation of a 2-million-year-old site or a 19th-century city neighborhood. Many archaeologists distinguish between three general forms of excavation: test pits, vertical excavations, and horizontal excavations. Test pits are small holes dug at spaced intervals to establish the extent of a site. Vertical excavations are trenches dug to the depth of sterile bedrock (bedrock that contains little or no organic or human-made material). Vertical excavations establish dates and sequences of human occupation of a site. Horizontal excavations cover large areas of land and provide information on the layout of entire campsites, villages, or city precincts. Modern horizontal excavations involve numerous small digs to reduce damage to the archaeological record.

Archaeologists rely on a wide variety of tools. These include bulldozers for removing sterile (empty) layers from the top of buried occupation layers, picks and shovels for removing smaller areas of sterile soil, hand adzes and trowels for careful excavation around buried materials, and delicate dental picks and brushes for cleaning skeletal remains and other fragile discoveries.

Archaeologists spend much of their time on digs identifying hard-to-recognize stratigraphic and occupation layers. They also locate inconspicuous site features, such as postholes, which are the filled-in indentations left by post beams used in houses and other structures; storage pits, where foods were once kept; and hearths. The diamond-shaped trowels used by archaeologists have blades that can scrape fine soil smoothly enough to reveal the precise edges of such features as postholes and buried remains.

Archaeologists also have specialized methods and tools for separating extremely small buried materials from the surrounding soil. They use fine mesh screens to search for items such as cereal grains and other plant remains, the bones of rodents and other small animals, and tiny artifacts such as beads. However, these screens are not delicate enough for the recovery of the tiniest plant remains, such as pollen grains and the smallest seeds. To recover these materials, archaeologists use a technique called flotation, in which sediments are mixed with water and the organic matter floats to the surface.

In a study in the 1970s at Abu Hureyra, in Syria’s Euphrates Valley, British archaeobotanist (specialist in ancient plant remains) Gordon Hillman ran large samples of deposits through water and fine screens. Using this method, he was able to recover thousands of cereal seeds. The seeds provided clues that the ancient village had suffered through drought. Hillman determined that the nut-rich forests that grew close to Abu Hureyra in 8500 BC must have retreated later during a long period of dry weather. The drought forced people to forage more for cereal grasses, including ancient forms of wheat and barley.

Until the second half of the 20th century, many archaeologists worked without the help of experts from other fields. Today, most archaeologists work with close-knit teams of trained excavators as well as with scientists from other disciplines who specialize in studying ancient environments.

For example, from the 1950s to the 1970s at Olduvai Gorge in Tanzania, an international team of scientists excavated a series of animal bone caches, places where early humans butchered animals and ate animal body parts. The researchers studied hundreds of stone tools and fragments found in the caches along with broken animal bones. They also gathered soil samples and freshwater shells in order to study the ecology of the area between 1.5 million and 2 million years ago, when the caches were in use. Microscopic analysis of the broken bones showed that some were stolen from predator kills, then broken up by hominids using stone tools, and later scavenged a second time by hyenas. Before this research, most anthropologists believed that humans became predatory hunters as soon as they had learned to make tools. The Olduvai research shows that humans were scavengers long before they began hunting on a regular basis.

Many excavations of Stone Age sites concentrate on base camps, places where small groups of generally nomadic foragers settled while they collected food resources from the surrounding area. Such projects involve excavation of the entire camp, including the careful dissection of hearths. Because hearths consist of ash and charcoal accumulations, they are important for radiocarbon dating.

Kill sites, places where hunters captured and butchered their prey, can also reveal valuable information. For example, in about 6000 BC, a group of hunters on the central plains of North America drove a herd of bison into a dry arroyo, or gully, near what is now Kit Carson, Colorado. In the late 1950s American archaeologist Joe Ben Wheat excavated the bones of about 190 bison jammed in the narrow arroyo. By carefully recording and studying the bones in their original positions, Wheat was able to reconstruct the hunting and butchering procedures used by the hunters.

Wheat found that the bison at the bottom of the pit, about 40 animals, remained unbutchered because the rest of the herd had fallen in on top of them. These untouched skeletons lay with their heads facing south, indicating the direction they were running when they fell into the arroyo. Because Wheat found projectile points lodged in the carcasses of only these lowest, inaccessible animals, he determined that the hunters had ambushed the herd, which then stampeded in the direction of the arroyo. Wheat also recovered numerous stone butchering and hunting tools among the top levels of butchered carcasses, also showing that this was a planned attack. The large number of bison meant that the hunters had ambushed a full herd. The herd included many juvenile and infant bison, which showed that the hunt had likely taken place in late spring.

There are various methods used to excavate sites that contain standing structures. The methods used depend on the size and complexity of the structures. Small structures such as mud-brick houses, adobe pueblos, and stone masonry dwellings are fairly easy to excavate, in part because of their size and the relative recentness of their burial. Sites of monumental architecture—large public and often sacred buildings—require special excavation methods. Evidence of religious activity may be particularly difficult to identify, so even large excavations must proceed carefully to preserve the smallest details. While excavations of masonry monuments such as the Egyptian pyramids or the Parthenon have been relatively straightforward, excavations of some ancient monuments have proved more difficult. For instance, sun-dried mud-brick temples built about 2800 BC by Sumerian architects, in what is now southern Iraq, had become almost undistinguishable from the clayey soil and sand that surrounded them. Archaeologists had to use air compressors to carefully blow away the surrounding soil and reveal the structures of the temples.

Excavation has been even more difficult for sites that contain arrangements of megalithic structures. At these sites, archaeologists have sought to understand the significance of the alignments of the stones and the relationships between individual stones. For instance, the multiple stone circles and arcs of Stonehenge in southern England were erected at different times during the Bronze Age, with construction culminating around 1800 BC. To establish the chronology of Stonehenge’s construction, numerous archaeological excavations since the early 1900s have removed earth and buried objects from around the bases of the structure’s rough, massive stone columns. Radiocarbon datings of charcoal fragments and precise stratigraphic excavations at the structure’s base show that Stonehenge was constructed in multiple architectural phases.

"How old is it?" While archaeologists seem to answer this question with ease, the answer is based on difficult science. Accurately dating an archaeological site requires the application of two distinct methods of dating: relative and absolute. Relative dating establishes the date of archaeological finds in relation to one another. Absolute dating is the often more difficult task of determining the year in which an artifact, remain, or geological layer was deposited.

Relative dating relies on the principle of superposition. This principle states that deeper layers in a stratified sequence of naturally or humanly deposited earth are older than shallower layers. In other words, the uppermost layer is the most recent, and each deeper layer is somewhat older. Relative chronologies come from two sources: (1) careful stratigraphic excavation in the field, noting the precise location of every artifact and remain within layers of earth; and (2) close study of the characteristics of artifacts themselves.

Archaeologists commonly use clay potsherds to develop chronological sequences for cultures of the Neolithic and later periods. Pottery was invented during the last Stone Age period, known as the Neolithic, which began about 10,000 years ago in the Middle East. Potsherds occur in such large numbers in most sites that researchers can collect only small samples of them in a single excavation. Using statistical sampling methods, archaeologists can use smaller numbers of artifacts, such as potsherds, to make accurate estimations of the total numbers of each type of artifact. Archaeologists use such statistical estimates to reconstruct sequences of past cultural change, as follows.

When studying potsherds or other artifacts, archaeologists record variations in characteristics such as material composition, form, style, and decoration. This information forms the basis for developing seriations (artifact sequences), which chronicle artifact evolution over hundreds or thousands of years. Pottery characteristics, like modern automobile designs and clothing fashions, changed over time, growing and then diminishing in popularity. By noting these changes, archaeologists can establish long sequences of artifact styles.

In the 1960s on an ancient village site in the Tehuacán Valley of present-day Mexico, Richard MacNeish examined hundreds of broken potsherds from dozens of sites. From these fragments, MacNeish documented a shift from plain to richly decorated vessels over a period of several occupations of the village. He developed a complete sequence of pottery styles across the entire valley from before 3000 BC to recent times. MacNeish also gave absolute dates to his sequence using radiocarbon analysis from charcoal found near and around potsherds.

Absolute dating, sometimes called chronometric dating, refers to the assignment of calendar year dates to artifacts, fossils, and other remains. Obtaining such dates is one of archaeology’s greatest challenges. Archaeologists who specialize in prehistoric periods use a variety of both well-established and experimental methods for absolute dating of ancient cultures.

Dating to Objects of Known Age  One of the simpler ways to determine the absolute age of an object is to find historical documents or objects of known age that confirm the date, or both. The earliest recordings of dates, documented in writing or some other form of decipherable notation, come from about 3000 BC in southwestern Asia. In other areas, people did not begin to record dates until far more recently. In the Americas, for instance, writing did not exist until after the 1st century AD; the civilizations of Mesoamerica, such as the Olmec, Aztec, and Maya, were the only civilizations in the Americas to have writing—the Inca of South America left no evidence of writing.

Artifacts with known dates, such as coins or pottery of a well-known period, provide archaeologists with comparisons that allow them to assign dates to other sites and cultures that did not have writing. For example, during his excavations of Knossos in the early 1900s Sir Arthur Evans also studied pottery vessels found in Egypt that were made by the Minoan inhabitants of Bronze Age Crete. Knowing the dates of the sites in Egypt where the vessels were found, Evans determined that the Minoan civilization, one of several to rule the island of Crete, flourished between 2000 and 1250 BC. Because of its dependence on writing, the method of using historically dated artifacts to date new finds can only be used on archaeological sites that existed after the advent of written records.

Dendrochronology, or tree-ring dating, was originally developed in the Southwest United States using the annual growth rings on long-lived trees, such as bristlecone pine. These growth rings fluctuate in width from year to year, depending on annual rainfall. By studying the growth patterns of many ancient trees that lived for long periods of time, researchers can create so-called master tree-ring patterns. These master patterns can be compared with pieces of wood found in archaeological sites. Thus, archaeologists can use wooden objects, such as house posts, to determine the age of artifacts and other remains. Since the 1920s, archaeologists doing research in the Southwest have used dendrochronology to date wooden beams from pueblos. The wooden beams have been well preserved in the dry heat of the area and have been used to precisely date sites such as Mesa Verde, Colorado, and Pueblo Bonito in Chaco Canyon, New Mexico.

In recent years, researchers have applied dendrochronology to European oaks and a variety of Mediterranean trees. Dendrochronologists have established tree-ring chronologies that extend to as early as 6600 BC in Germany. Using these tree-ring chronologies, archaeologists have been able to date the earliest farming in central Europe to between 6000 and 5000 BC. Tree-ring dating has also allowed scientists to date drought cycles that may have been important in the rise and fall of cultures in the Mediterranean and Aegean regions. At the site of one of the world’s earliest farming villages, Çatal Hüyük in Turkey, British archaeologist Ian Hodder used a tree-ring sequence to date individual houses within the settlement that existed in about 7000 BC.

Radiocarbon dating was developed by American chemist Willard Libby and his colleagues in 1949, and it quickly became one of the most widely used tools in archaeology. Radiation from space produces neutrons that enter the earth’s atmosphere and react with nitrogen to produce the carbon isotope C-14 (carbon 14). All living organisms accumulate this isotope through their metabolism until it is in balance with levels in the atmosphere, but when they die they absorb no more. Because the nucleus of C-14 decays at a known rate, scientists can determine the age of organic substances such as bones, plant matter, shells, and charcoal by measuring the amount on C-14 that remains in them. See also Dating Methods: Carbon-14 Method.

Radiocarbon methods can date sites that are up to 40,000 or 50,000 years old. These methods have revolutionized archaeology over the past half-century. For instance, radiocarbon testing of materials from early farming settlements at Jericho, in what is now Jordan, dated these settlements to as early as 7800 BC, indicating that they are more than 3500 years older than was once thought.

In recent years, scientists have developed a new approach to radiocarbon dating using a device called an accelerator mass spectrometer. This device directly counts C-14 atoms, rather than counting rates of disintegration. Accelerator mass spectrometry (AMS) can date a sample as small as a single kernel of grain or a fleck of wood preserved inside a bronze axe socket. This method can date items that are up to 90,000 years old.

Since AMS dates can come from very small, isolated objects, the resulting chronologies can be much more accurate than those from standard radiocarbon dating. For example, American archaeologist Bruce Smith used AMS to date individual maize cobs from caves in the Tehuacán Valley. His results indicated that domesticated corn was grown there by about 2500 BC, much later than earlier radiocarbon dates had suggested.

Radiocarbon dates are approximations, and they are published with statistical margins of error. For instance, a date may be given as 30,000 BC ± 2000 years. However, the radiocarbon dates of objects less than about 8000 years old are also compared with and calibrated to dates from tree-ring analysis. These estimates can pinpoint the age of an object with great precision, often to within 100 years.

Potassium-argon dating provides approximate dates for sites in early prehistory. Geologists use this method to date volcanic rocks that may be as much as 4 billion to 5 billion years old. Potassium is one of the most abundant elements in the earth’s crust. Many minerals contain radioactive K-40 (potassium 40) isotopes, which decay at a known rate into Ar-40 (argon 40) gas. Scientists use a device called a spectrometer to measure the accumulation of Ar-40 in relation to amounts of K-40. The ratio of these elements can indicate the age of a geologic layer, generally since it last underwent a metamorphosis, such as melting under the heat of molten lava from a volcanic eruption. Thus, geologic layers rich in volcanic deposits lend themselves to potassium-argon dating.

Prehistoric archaeological sites such as the Koobi Fora area of East Turkana, Kenya, and Olduvai Gorge in Tanzania, both of which formed during periods of intense volcanic activity, have been dated using the potassium-argon method. However, such dates commonly have a high margin of error. For instance, in the 1960s British archaeologist Glynn Isaac studied a site in a layer of Koobi Fora in which it appeared early humans had butchered animal carcasses. Isaac dated the site at 2.6 million years old, with a margin of error of over 250,000 years.

Archaeologists also use more experimental methods of absolute dating. Electron spin resonance (ESR) measures the electrons captured in bone or shell samples up to 2 million years old. ESR testing on human tooth enamel from Skhul Cave in Israel dates some of the earliest anatomically modern humans in southwestern Asia to about 100,000 years ago.

Uranium series dating measures the radioactive decay of uranium isotopes in rocks made up of calcium carbonates, such as limestone and calcite. This technique may be used to date bones and tools embedded in these rocks. For instance, in 1994 archaeologists Allison Brooks and John Yellen used uranium series dating to determine the age of early African fish spears made of animal bone. The spears, which came from Katanda in the present-day Democratic Republic of the Congo, are thought to date to about 20,000 years ago.

Thermoluminescence is a technique that measures electron emissions from once-heated materials, such as pottery or rocks that were once exposed to solar or volcanic heat. Many thermoluminescence tests have produced unreliable results. Archaeologists are attempting to refine the technique.

Once a site has been documented, mapped, and dated, the archaeologist tries to integrate all the data into a coherent and understandable picture of the past. Archaeologists draw from what is already known of the archaeological record to develop their interpretations. Their new interpretations then add to that body of knowledge.

Everyone classifies objects—we know the difference, for example, between eating utensils and automobiles. We also make choices among objects—we choose a spoon to eat soup and a fork for salad, and we use large trucks to carry loads but small cars to save gas. The objects that archaeologists study were all once classified in similar ways by the people who originally made or interacted with those objects. Thus, archaeologists classify their finds to help them understand past cultures.

In archaeology, classification is a research tool that is used to distinguish among different artifacts and other material objects. Archaeologists use various systems of classifying artifacts to organize data into understandable units. Archaeological classifications describe artifact types, such as different forms of pottery, as well as relationships among different objects of a common type, such as clay vessels. Archaeologists call this system typology—a hierarchical classification based on artifact types and groupings.

When studying thousands of stone tools or potsherds, archaeologists search for patterns in them, such as of shape, color, and material composition. These patterns become the variables that define each category of object. For example, the category "containers" may include such objects as shallow bowls and round-based pitchers with curved handles.

After grouping the artifacts from an excavation into specific types, archaeologists determine the sequence in which those artifact types existed in the past. The process of determining this sequence is called seriation. Archaeologists believe that sequences of artifact types, or seriations, illustrate how past cultures changed over long periods of time.

Archaeologists often analyze artifact type sequences from many sites covering large areas of land. The comparison of multiple type sequences can show how particular types of artifacts spread from one group of people to another in the past. For example, during a period of over 1000 years beginning in about 1500 BC, a distinctive shell-ornamented pottery known to archaeologists as Lapita ceramics spread widely from one island to another in the southwestern Pacific. The continual evolution of Lapita pottery and other items across islands shows that the people maintained an extensive canoe trade in volcanic glass and other materials.

From the earliest times, human societies have exchanged raw materials and manufactured items with their neighbors and even with people living in other areas. People have traveled particularly far for valued materials—such as the best toolmaking stones, metal ores, and seashells—or for artifacts not manufactured locally, perhaps mirrors or wrought metal tools. When archaeologists find known artifact types far from their place of origin, they can begin to piece together ancient patterns of trade. For example, Celtic tribes in central and western Europe imported wine in Greek vessels from Mediterranean lands sometime around 200 BC. Several archaeological studies have traced the extent of this trade by plotting the distribution of such vases along the Rhine and Rhone river valleys.

Increasingly, archaeologists are turning to techniques that allow them to trace the source of materials in ancient trade. For example, analyses by George Bass and Cemal Pulak of the copper ingots they recovered from the Uluburun shipwreck off southern Turkey showed that the copper came from mines in Cyprus. Numerous analyses of this type have revealed that trade assumed increasing importance over time during the ancient past, especially with the rise of early civilizations in Egypt and Mesopotamia after 3000 BC.

Until the 1950s, archaeologists were concerned mainly with the study of artifacts and cultural sequences. However, the increased use of radiocarbon dating and of computers and other high-technology scientific methods in archaeology led to a major theoretical revolution in the 1960s. This new approach to archaeology placed a major emphasis on environmental reconstruction, the study of ancient ways of life, and the use of advanced analytical tools. Above all, researchers practicing this new form of archaeology stressed the importance of explaining how past cultures developed and changed. Because they were primarily interested in cultural process, these archaeologists came to be known as processual (process-oriented) archaeologists and their work as processual archaeology.

Processual archaeologists think of human cultures as systems that interact with their surrounding ecosystems—interdependent systems of plants, animals, landscapes, and the atmosphere (see Ecology: Ecosytems). Processual archaeologists collect large amounts of environmental data in order to understand these relationships. To processual archaeologists, major cultural developments, such as the origins of agriculture and civilization, are highly complicated sequences of events that involve a series of interacting and constantly changing factors. Many earlier archaeologists, by contrast, believed that such developments were the result of single causes, such as a change in weather patterns or an increase in human populations.

For example, British archaeologist Barry Kemp took a processual approach to explaining how ancient Egyptian chiefdoms became a single unified state. In 1989 Kemp suggested that a number of interacting developments gave rise to the unified state along the Nile River valley, which he dated to within a few centuries of 3000 BC. His analysis of Egyptian ceramics, religious art, and trade routes has shown that a variety of factors—including population growth, the development of new religious beliefs, and expanded trade—contributed to this important change.

Many archaeologists now support the processual approach to research and interpretation, but others have criticized it and developed new approaches. Critics say processual archaeology is too impersonal and too focused on scientific methods. Many archaeologists have begun to use their research to tell stories about the people of the past, and about how those people interacted with one another in large and small groups. These new approaches to interpretation are loosely called post-processual archaeology. This name covers many types of research, but all of it focuses on what people in the past did and thought from day to day.

Post-processual archaeologists seek to reconstruct past people’s beliefs and value systems. They believe that most archaeology has incorrectly presented societies as homogenous. Post-processual archaeology focuses on how past societies, like living ones, were made up of many smaller groups. Past societies comprised different types of families, ethnic groups, gender groups, age groups, and social classes. All of these groups interacted with one another, and this interaction drove much cultural change. For this reason, understanding the everyday lives of ordinary people has become as much of a concern for archaeologists as understanding the larger processes of cultural change and evolution.

Post-processual archaeology’s focus on the lives of small, specific groups of people—especially those not well documented in historical records—relies on both meticulous excavation and careful analysis of often seemingly insignificant artifacts. For instance, in excavations in the 1980s of slave quarters on President Thomas Jefferson’s late-18th-century estate of Monticello in Virginia, American archaeologists William Kelso and Diana Grader found discarded animal bones of cows and pigs. The researchers determined that some of Jefferson’s slaves had higher status and ate good cuts of beef, while other, lower status slaves ate poorer cuts of pork.

Archaeologists in the United States have excavated thousands of African American residences from the 18th, 19th, and early 20th centuries. Excavated sites include buried neighborhoods once occupied by black residents in Philadelphia, Pennsylvania, and slave quarters on South Carolina plantations. In most of these excavations, distinctive clay vessels and other artifacts, as well as the structure and arrangement of houses, reveal an African American culture that had strong ties to its West African roots. Recent studies by American archaeologists have also examined the lives of textile workers in New England, Catholic missionaries in the desert Southwest, residents of Midwestern frontier forts, and Chinese fishing villagers in San Francisco, California.

Even recent eras in history lie buried under the streets and buildings of present-day cities and towns. Excavations under the streets of New York City, for example, have uncovered a hitherto undocumented 18th-century African American cemetery. Research in Annapolis, Maryland, has revealed a far more ethnically diverse population than many historical accounts suggest; multiple excavations around the port of Annapolis have recovered artifacts from many parts of the world.

Historical archaeologists studying small and diverse groups of people often check their interpretations of the past against written and even spoken accounts that have been passed down over generations. In some cases, historical accounts give archaeologists ideas about what to look for in excavations and clues to the meaning of what they find. In other instances, differences between the historical record and the archaeological record tell researchers much about what is hidden in or omitted from historical accounts.

The study of gender is a combination of many archaeological approaches. It involves processual perspectives, comparative observations from living societies, and new interpretations of the archaeological record. Many studies have focused on relationships between men and women, and on how gender roles developed and changed in the past.

An example of how archaeology can provide information about gender comes from Syrian farming villages of 8000 BC. Archaeologists know that women in these villages ground the grain because the knee bones of their skeletons show scars caused by the constant stress of kneeling and pushing on grinding stones. This relatively straightforward study is based on bone pathology. Other research into past gender roles and relations involves detailed analyses of such artifacts as potsherds and food remains found in people’s homes. For instance, Classic Maya figurines of males and females differ in style. Maya figurines of men are much more ornate than those of women, indicating that Maya women had relatively low status compared with Maya men. The plain, unadorned style of Maya female figurines persisted over time, which indicates to archaeologists that women had very fixed gender roles.

The archaeological record is an exhaustible resource. For centuries, people have dug up the record with impunity, destroying it while plowing or mining, quarrying it for stone, or looting it for valuable treasures. Archaeologists themselves have, in the past, excavated thousands of sites with little concern for long-term conservation of the sites. Since World War II ended in 1945, the pace of destruction has accelerated due to a massive expansion of activities such as road building, transit and sewage system construction, and strip-mining. A thriving international trade in antiquities of all kinds has also fueled widespread destruction.

At the same time, archaeology has expanded dramatically. A century ago there were a handful of professional archaeologists throughout the world. Now there are thousands. The development of passenger jet airplanes and the growth of tourism have transported thousands of people around the world to visit archaeological treasures such as the pyramids in Egypt; the Parthenon in Athens, Greece; and the ruins of the ancient cities of Mesoamerica. Many sites are wearing down due to excessive visitation. Archaeologists have become increasingly concerned about the future of the past, and many have turned their attention to problems of conserving and managing the archaeological record.

Archaeologists today use the term cultural resource management (CRM) to refer to all efforts to preserve and repair damage to the record, and to repatriate artifacts and remains—that is, to return them to their rightful owners. A large part of CRM is concentrated on examining and modifying archaeological survey and excavation techniques. CRM also works toward conducting careful analyses in advance of activities such as road construction. CRM seeks to record and salvage sites that are in danger of being destroyed and to minimize the impact of modern disturbance, while managing archaeological resources for future generations. CRM now accounts for most U.S. archaeological research, but this effort still has not prevented the destruction of thousands of unidentified or uninvestigated sites.

Since the beginning of the 20th century and increasingly since the 1960s, both federal and state authorities in the United States have enacted antiquities and historic preservation legislation aimed at protecting the archaeological record. For instance, the U.S. Historic Preservation Act of 1966 set up a national framework for the preservation of historic sites, including archaeological sites. The National Environmental Policy Act of 1969 established a requirement to conduct archaeological surveys in response to proposed federal use of land and natural resources. The Archaeological Resources Protection Act of 1979 also laid down stringent protections for archaeological sites over 100 years old. All of these acts are still in force. Countries throughout the world have passed similar legislation.

Recent legislation in some countries—such as Australia, Canada, and the United States—has also established the right of indigenous peoples to exercise some control over the remains of their own pasts. For instance, the U.S. Native American Graves and Repatriation Act was passed in 1990. This act establishes the rights of Native Americans, whose ancestors occupied the lands of the Americas for thousands of years, to make decisions about excavations and the study, display, and storage of artifacts and remains. This legislation requires the return of human remains and sacred artifacts to living groups that have direct ancestral ties to the original owners. Native American groups may rebury repatriated items or dispose of them as they wish.

Present-day societies can learn much from their predecessors. Applied archaeology refers to archaeological research that is designed to have practical and educational significance for modern societies. In the highlands of Bolivia and Peru, for instance, archaeologists have reconstructed systems of elevated fields and canals that once allowed ancient farmers to grow potatoes without losing them to frost. Farmers in these regions today have learned to use this same technique with great success.

Since the 1960s, urban archaeologists have dug deep under modern cities such as London, Paris, and New York City, uncovering earlier cities that lie beneath streets and skyscrapers. These excavations help explain much about urban life today and also provide important information for city planning. For instance, they have provided information about the origins of social classes and the foundations of modern infrastructure, such as sewage systems.

American archaeologist William Rathje has taken urban archaeology a step further and excavated modern municipal garbage dumps in Tucson, Arizona, and many other U.S. cities. Rathje analyzes people’s trash to determine things about their income, class, race, age, and health status. His work has led to a better understanding of the consumption and waste patterns of our own society. It has also provided comparisons for gaining new insights on the historical archaeological record.

Through the study of human evolution, archaeology fosters an appreciation of our common ancestry. The discovery of thousands of unique cultures in the archaeological record also highlights the amazing scope of human diversity. Recent genetic research, in tandem with an accumulation of archaeological research, indicates that all people descended from a single human stock that originated in tropical Africa between 100,000 and 200,000 years ago. Archaeology also documents the origins and development of diverse cultural patterns, the continuity of traditions, and the exchange of ideas and beliefs across cultures.

Archaeology was once a predominantly academic science that was conducted in universities and colleges; today, archaeology is increasingly becoming a profession. Until recently, becoming an archaeologist meant obtaining a doctoral degree and a university professorship or a position as a museum curator. Many archaeologists now earn master’s degrees and work for government agencies or for private environmental monitoring companies and organizations. In the future, archaeology will be more concerned with monitoring the archaeological record than with making sensational discoveries. The archaeologist’s main concern will be to preserve the world’s human cultural and biological heritage for future generations.