Archaeology is the science of finding and studying evidence of human life in the past. Some of this evidence, such as old buildings and ruins, is still visible today. But most of the evidence is now buried under fields or beneath modern buildings. As a result, archaeologists spend a lot of time carefully digging in search of old objects and other evidence.
Archaeologists study a very wide variety of objects. Sometimes they find things that were deliberately buried underground, such as the treasures in the tomb of the pharaoh Tutankhamen. Sometimes they find things that were lost accidentally, such as coins fallen from somebody’s purse or pocket. But most of what they find is rubbish—objects that people threw away because they were broken or worn out. Objects made of wood, leather and textiles decay fairly quickly, and these are rarely discovered. Objects made from metal also decay, only more slowly, and these are quite rare. Objects made from stone, glass and pottery survive the best, and these are what archaeologists usually find when they dig.
LAYERS OF THE PAST
Archaeology is based on stratigraphy, which is the idea that newer objects are found closer to the surface, and older objects are found deeper in the ground. Almost anything left out in the open will eventually decay or become buried in the ground through natural processes. Over hundreds and thousands of years the wind and rain cover everything with a layer of dust and soil. In desert lands, entire buildings have been buried beneath wind-blown sand. In towns and cities the burying process is part of human activity. People knock down old houses and build new ones on top. In some cities this has been going on for thousands of years, and modern buildings sit on top of a mound of many layers of flattened old buildings.
WHERE DO ARCHAEOLOGISTS DIG?
Sometimes it is easy for archaeologists to know where to dig. There may be bits of stone wall still sticking out of the ground. Or there may be a mound of earth that does not look like a natural feature. In the past, people were sometimes buried beneath small mounds. A large mound might be the remains of an old fortress or even a whole town. Other discoveries are made by accident. Farmers ploughing a field might find bits of broken pottery, or workers making a new road might uncover the foundations of an old house. Then they call in the archaeologists.
HOW DO ARCHAEOLOGISTS DIG?
A place where archaeologists are working is usually called an excavation or ‘dig’. They first measure the site and mark it out into a network of squares. They only work in a few squares at a time. Archaeologists work by digging a trench. Everything that comes out of the trench is examined very carefully. The soil is sieved to see if there are any plant seeds or tiny fragments of bone or pottery. Even the colour of the soil is important. Places where the soil changes colour might show where there used to be a wooden post that supported the roof of a hut. The wood has long rotted away, but it has left a stain in the soil.
Buried objects are often very delicate and fragile because they have been weakened by decay. Archaeologists have to learn to dig very gently, and they often use soft brushes to patiently remove the soil from a buried object. They photograph and measure every object, both before and after they remove it from the ground. Every detail is carefully recorded. By itself, the evidence from a single dig can only reveal a very limited amount of information. But by comparing the results of many different digs, archaeologists have been able to put together a picture of life in the past.
THE THREE AGES OF ARCHAEOLOGY
The first archaeologists were sometimes little more than treasure-hunters. They excavated ancient temples and palaces searching for impressive objects to put in museums. During the 19th century, archaeology became a science, and archaeologists began to study everyday objects and the remains of ordinary settlements. In 1836, after studying old tools found in local fields, the Danish archaeologist Christian Thomsen was able to divide early human history into three ages, one after the other, according to the material they used to make knives. The earliest was the Stone Age, then the Bronze Age and the Iron Age. In Western Europe, the Iron Age ended with the coming of the Roman Empire.
Other archaeologists began to use Thomsen’s three-age system to describe the date of objects and other evidence that they discovered, and this system is still used today. As they gathered more evidence of the past, archaeologists tried to develop more precise methods of dating objects. They studied the way that the decoration of pottery and other objects changed over time, as different styles came in and went out of fashion. These studies enabled them to say which styles were earlier and which were later, but they did not provide any actual dates.
HOW DO ARCHAEOLOGISTS GET THE EXACT AGES OF OBJECTS?
In the 20th century archaeologists were able to use radiocarbon dating to get precise dates for the first time. Radiocarbon dating can only be used on substances that were once living, such as bone, natural fibres and plant remains (including wood and charcoal). Radiocarbon dating works by measuring the amount of a substance known as carbon 14 that is produced by all living things. After death, the amount of carbon 14 starts to decline at a steady rate. By measuring the carbon 14 in old bones or charcoal, scientists can tell how long they have been buried. Archaeologists often find bones and charcoal buried alongside pottery and metal objects, and so they can date these items too.
Archaeologists often have to work in difficult conditions, at the bottom of deep trenches that keep filling with water, in rivers and even under the sea. Modern technology, such as scuba breathing apparatus, has enabled archaeologists to excavate shipwrecks on the sea bottom. Some wrecks have been lifted to the surface and placed in museums. Wrecks that are too deep for people to visit easily are explored using underwater robot cameras and remote-controlled submarines.