To determine the oldest layer in the rock cliff, we need to consider the principles of stratigraphy, particularly the Law of Superposition. According to this law, in undisturbed sedimentary rock layers, the oldest layers are at the bottom, and the younger layers are at the top.
If the scientist has a drawing of the rock layers, we would generally look at the arrangement of the layers. Assuming that layers are numbered from bottom to top in the drawing, the oldest layer would be the one with the lowest number.
Since the scientist noted that layers 3 and 7 were formed from cooled lava, this suggests these layers are volcanic in nature. However, we cannot definitively say which of these layers is older based solely on their composition without their positions relative to other layers.
Thus, if we assume that layers are arranged sequentially and layer 1 is at the bottom, then layer 1 would be the oldest. However, if layer 1 is younger than layers 3 and 7, then we could refine this answer by looking more closely at the drawing.
In conclusion, without viewing the actual drawing, the oldest layer is typically the lowest one, following the Law of Superposition, but specific identification depends on the arrangement of the layers as represented in the scientist's drawing.
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