Archeologists work by digging into sites and collections. When they excavate, archeologists use tools you might recognize.

Putting together a story from archeology is like doing a big puzzle without the box lid. Artifacts are some of the pieces, but only part of the total picture. Keep going to find out how archeologists put the puzzle together.

"Where do we start?" An archeologist scans a field. A glint of white catches her eye. She bends down to see a piece of ceramic and some rusty nails. Marking the cluster of artifacts with flags, she keeps looking, but this looks like a good spot to excavate.

A site survey helps archeologists narrow down where to start. They mark likely places and dig small, but controlled, test pits to get a preview of what they might find. Sometimes computer-driven equipment helps them to see into the ground.

Who cares about being a professional maker of measurements? Archeologists do. Careful measurements are important to make a good record of a site.

Archeologists use geometry to lay out excavation units and triangulate the locations of features. They start from a datum point. Peering through a transit measures across sites. A plumb bob weighs down the string to make measuring depth easier.

Excavation is the way archeologists look below the surface. Excavation destroys an archeological place, so archeologists are very careful about how and where they dig.

Archeologists grid a site before excavating. Then, layer by layer, unit by unit, they use different tools to dig, photograph, and draw what they see. They also take soil samples and bag up artifacts. If they're lucky, they find features like ancient cookstoves or wells or even buildings.

• Try it: Peanut Butter and Jelly Archeology (Hopewell Culture NHP)

Each new layer of soil, or stratum, signals a different cultural time period. See how the soil layers change color? A stratum might be a few centimeters or many feet thick. Soil layers usually get older the deeper they go. Archeologists dig until they hit subsoil, a layer without artifacts.

Sometimes archeologists name and date the layers from the artifacts, the texture of the soil, and careful mapping. They put this information into a timeline for the site.

• Try it: Mapping and Excavating a Jello Mold (.pdf) (www.texasbeyondhistory.net)

Buckets and shovelfuls of dirt are dumped in a screen held by a wooden frame. Shaking the screen really hard leaves behind artifacts, stones, and debris. The artifacts go in labeled paper bags to study later. Sometimes archeologists take samples of soil for analysis.

For tiny objects, like beads and seeds, archeologists shoot water through a fine mesh screen in a process called waterscreening.

Good recordkeeping is really important. Archeologists make notes and draw interesting finds the entire time they excavate. The records describe what the archeologists saw in the units. Photographs and maps are another kind of documentation. They show what archeologists saw.

If you've visited an archeological site, then you have seen how old archeological photographs and records help us learn about the past.

A sheep is a sheep is a sheep, right? Perhaps. Remember the different kinds of archeologists? Each one uses what they know to look at sheep in a different way.

During a dig, they pool ideas to find all the possible sheepish meanings. Maybe they see sheep images on rocks. Or excavate a historic sheep farm. Or study how grazing sheep change landscapes. Or wonder about the uses for sheep. Or head to collections to compare the faunal finds to another site.