BOB HIRSHON (host):
Archaeology’s hidden layers. I’m Bob Hirshon and this is Science Update.
David Schwan of Fremont California wrote with this question: When archaeologists uncover ancient cities, why do they have to dig so deep? For the answer, we turned to archaeologist Kathryn Bard of Boston University.
KATHRYN BARD (Boston University):
Often, they are digging through centuries of buildup of houses and other structures. And so, frequently, when a house collapses for one reason or another, then another house is built on top of it; the same is true of ancient temples, so this accumulates a lot of deposits over centuries. And if you want to go to the early part of the site, you have to dig down through much later parts.
And natural processes such as decomposition, plant growth, and weather can all contribute to the decay of earlier structures and the layering of archaeological sites. If you have a science question, call us at 1-800-why-isit. I’m Bob Hirshon, for AAAS, the science society.