Question

the diagram below represents a cross section of the earths crust showing rock units and a fault. the rock layers are not overturned. which rock unit is the youngest? sandstone basalt limestone shale

Explanation:

Step1: Apply the principle of superposition

In undisturbed sedimentary rock layers (shale, sandstone, limestone here), the lower layers are older. So shale is older than sandstone, and sandstone is older than limestone.

Step2: Consider the principle of cross - cutting relationships

Basalt (a volcanic rock) cuts through shale, sandstone, and limestone. According to the cross - cutting relationships principle, the rock that cuts through other rocks is younger.

Answer:

Basalt