Question

1. how were we able to predict which rocks were underneath the supai sandstone at mile 20? (refer to rock correlation model as needed)

Explanation:

Geologists use rock correlation, which involves matching rock layers (strata) across locations by their lithology (rock type), fossil content, and relative age principles (like superposition, where older rocks lie beneath younger ones). At Mile 20, the Supai Sandstone is a younger layer, so by correlating exposed sequences at other sites where rocks below the Supai are visible, and using consistent stratigraphic patterns, we can predict the underlying rock units. This relies on the principle that sedimentary rock layers form in predictable, sequential order that can be traced across regions.

Answer:

We predicted the rocks beneath the Supai Sandstone at Mile 20 using rock correlation, applying stratigraphic principles (like superposition, which states older rocks underlie younger ones) and matching lithology, fossil records, and known sequential rock layer patterns from exposed outcrops in nearby areas where the full stratigraphic sequence is visible. This allows extrapolation of the consistent, ordered rock layers to the Mile 20 location.