4. Scientists often use the relative positions of fossils in sedimentary rock layers to draw conclusions about the sequential nature of groups of organisms in the fossil record. Why are scientists able to
use such observations as a key to the relative ages of fossils?
a. Sedimentary rocks are laid down in layers, so the oldest layers in an undisturbed
rock bed will be located beneath upper layers.
b. Even when sedimentary rock layers are disturbed, the oldest layer is always
deposited on top of the youngest rock layer.
c. Younger rock layers are always deposited under older layers.
d. Weathering and erosion expose fossils making them easier to examine.