An archaeologist searches for both treasures and trash -- the signs of our earliest ancestors, a lost civilization or our recent past. After intensive study, extensive mapping and a painstaking dig, an archaeologist discovers a find. It might be a fragment of bone, a shard of clay or an ancient coin. As the dust and dirt settle through the archaeologist's screen, an irregular clump of clay appears. The clump doesn't crumble under light pressure. The archaeologist knows it's actually a potsherd, clay pottery tough enough to withstand the stresses of millennia.

Years of studying taxonomy might help the archaeologist roughly date the fractured fragment on-site -- eliminating the possibility that it's actually just a grungy plate from the recent past. Other consultants are soon brought in -- geologists, biologists or art historians -- people who help create an accurate, complete context for the little shard of clay. Piece by piece, history emerges from the earth.

Archaeology is the study of humanity's material remains: its buildings, art, everyday objects, trash and even bodies. Archaeologists are scholars who study every facet of their scholarly realm. They're explorers who map out and chart excavation sites. They're scientists who document and verify their finds. And they're historians who flesh out the past.

Because archaeology is such a massive field, it's usually broken into periods, like Prehistoric or Industrial archaeology, or into geographical areas, like Classical or Mesopotamian archaeology. Sometimes archaeology's subfields are practically independent disciplines. For instance, forensic archaeologists work with law enforcement officers to locate evidence or study potential gravesites. Underwater archeologists study shipwrecks or other watery remains of human industry and must be proficient divers. Archaeologists are sometimes confused with paleontologists, scientists who study the remains of prehistoric plants and animals, but not humans or our hominid ancestors.

Today archaeology is a precise science. Archaeologists' tools include radioactive carbon dating and geophysical prospecting. The discipline is strongly influenced and even driven by humanities like history and art history. However, it is, at heart, intensely methodical and technical. But archaeology hasn't always been precise. In fact, it hasn't always been a science.

Archaeology originated in 15th and 16th century Europe with the popularity of collecting and Humanism, a type of rational philosophy that held art in high esteem. The inquisitive elite of the Renaissance collected antiquities from Greece and Rome, considering them pieces of art more than historical artifacts.

The desire for antiquities and an interest in the ancients soon led to sponsored excavations and the development of Classical archaeology. Herculaneum and Pompeii, the two famous cities destroyed and preserved by the A.D. 79 eruption of Mount Vesuvius, were excavated in part because the Queen of Naples longed for ancient statuary.

Scientific archaeology continued to develop in the 19th century with advances in the studies of geology and biology. Charles Lyell helped spread the modern geologic system of uniformitarian stratigraphy, which gave archaeologists a reliable timescale on which to date items. The work of Lyell and the publication of Charles Darwin's "The Origin of Species" soon popularized the idea of evolution. Belief in man's antiquity exploded the study of prehistoric archaeology.

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. Sometimes such thoroughness can cripple a city. Rome struggles to meet the demands of its 2.8 million citizens while preserving its history

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.