A scientist is studying a section of exposed sedimentary rock layers that are near a fault line (a
place where the crust is actively moving and broken). Using the geologic principles discussed
in this lesson, name the principle that you think could explain this observation and give a
reasonable explanation as to why you think so.

Observation:
Layer A - top layer - contains fossils dated at 20,000 years old.
Layer B - next layer down - contains fossils dated at 100,000 years old
Layer C - third layer down, contains fossils dated at 400,000 years old
Layer D - bottom layer contained fossils 800,000 years old.

Principle of cross-cutting relationships

Explanation:

The geologic principle that will provide the most profound explanation to this problem is the principle of cross-cutting relationships.

It states that "features that cross-cuts rocks are younger than the layer they cut through".

Some of these features are intrusions, faults and joints.

The logic behind this reasoning is that without the rock in place, the cross-cutting event wouldn't have been recorded.

We can liken this to a fracture on the wall of a building. If the wall is not erected, there wouldn't be any fracture. Therefore, the fracture is far younger than the wall.