During the Dig
Archaeologists have the very important task of preserving the past in order to increase our knowledge of human society and past cultures. That actually is a very difficult task... because the archaeological process is very destructive. Several levels of human activity can be located atop one another and in order to reach the oldest one (the one at the bottom), the top layers have to be removed. The removal of these layers means that they will be destroyed. Forever.
Archaeologists are aware of this problem and, for this very reason, we keep detailed records, make copious notes, take several photographs, and make drawings and plans so that later generations can still study these layers even if they are gone. We also leave unexcavated areas so that future archaeologists with newer techniques and different equipment can dig on site as well.