For an artifact to have meaning and relevance, an archeologist must be able to assign it a date. Archaeologists have used a variety of techniques to make sense of the past:
- Self-dating: An item like a coin already comes with a date -- no questions asked.
- Relative dating: The date of an unknown item can be interpreted by the known dates of surrounding items.
- Clay-varve counting: Man's written chronology only goes back 5,000 years but by counting layers of varves, laminated sediments that accumulate annually, geologists and archaeologists can extend this chronology significantly.
- Dendrochronology: By counting the growth rings of trees, archeologists can compile a chronology or historical record and precisely date wood.
- Radioactive carbon dating: By measuring the activity of radioactive carbon, or carbon-14, archeologists can establish a chronology that dates back about 50,000 years.
- Potassium-argon dating: Archaeologists can establish the date of minerals and rocks by comparing rates of radioactive argon to radioactive potassium. Potassium-argon dating can set a chronology that dates back at least 2,000,000 years. This type of dating helped determine the age of the earliest man's remains.
- Thermoluminescence: By measuring the intensity of light energy, archaeologists can determine how long a substance was exposed to radiation
An Archaeologist's Work: Fieldwork and Excavation
It's easy to imagine the archaeologist in the field -- a modern-day adventurer discovering the mysteries of the past before whisking off to a new, even more fascinating site. The archaeological process, however, begins long before the spade hits the dirt. Every excavation involves years of study, scouting and planning.
Some archaeologists consider fieldwork the entire outdoor archaeological process, from scouting to digging. Others consider fieldwork the pre-dig activity and differentiate it from actual excavation. This preliminary work includes everything from consulting aerial photographs, old maps and physical references in literature, or even using high-tech methods like geophysical prospecting, a technique that measures electrical conductivity in soil.
This type of meticulous fieldwork prepares archaeologists for planned excavations. However, not all excavations are planned; there are also accidental excavations and rescue excavations. Some of the greatest archaeological finds are simply fortunate discoveries. In 1940, four French schoolboys found themselves in a chamber ornamented in Upper Paleolithic masterpieces. They had simply been exploring a tunnel exposed by an uprooted tree. In 1947, a Bedouin shepherd discovered the first Dead Sea Scrolls, the earliest copies of any Biblical books, while searching for a stray animal.
Sometimes, accidental finds become rescue excavations. Construction projects often unearth archeological sites that must be explored and recorded quickly so that business can continue. When a city has as many layers of history as Rome, archeological finds are inevitable; every request for a building permit -- all 13,000 annually -- requires an archaeological evaluation [source: National Geographic]. Sometimes such thoroughness can cripple a city. Rome struggles to meet the demands of its 2.8 million citizens while preserving its history [source: U.S. Department of State].
But because excavation inherently destroys a site, an archaeologist must record the placement of every artifact. This record ultimately becomes a primary source for other archeologists and historians to consult since the actual primary source -- the site itself -- no longer exists in its original form. The archaeologist also brings in experts from other disciplines like geology or metallurgy to help analyze the finds.
In the next section, we'll learn about archeology's dark side: smugglers, robbers and bungling amateurs.