Final answer:
The presence of the same fossil clam in layers of limestone associated with sandstone both in Europe and North America indicates these layers were deposited during the same geological period, following the principle of superposition. This aids in the relative dating of the rock layers.
Step-by-step explanation:
The question pertains to the relative dating of rock layers and the age of fossils. By observing that the same fossil clam is found in a layer of limestone above sandstone in Europe and below sandstone in North America, we can make inferences about the relative ages of these rock layers. This is grounded in the principle that in undisturbed sequences of sedimentary rocks, layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top.
Given that the same fossils are present in both continents, it indicates that these layers were formed during the same geological time period. This reflects the concept of correlation, which geologists use to match rocks and fossils from separate locations. In sedimentary environments, where limestone, silt, clay, and sand are deposited simultaneously in a continuous layer, the presence of the fossil clam helps us to establish a time marker across vast geographic areas.