An igneous intrusion cuts through three layers of sedimentary rock. Which rock is the youngest?

Well, this sounds like quite the rocky situation! In terms of the sedimentary rock layers, the youngest rock would be the one closest to the surface. However, it seems like the igneous intrusion had other plans and decided to make an entrance! So, in this case, the igneous intrusion would be the youngest, as it cut through the sedimentary layers like a hot knife through butter. Don't worry, though, rocks may be old, but they'll never pass up an opportunity to rock out with some spicy geological action!

To determine which rock is the youngest, we need to apply the principles of relative dating.

The principle of cross-cutting relationships tells us that any feature, such as an intrusion or fault, that cuts across other rocks must be younger than the rocks it cuts through.

In this case, the igneous intrusion cuts through three layers of sedimentary rock. Therefore, the rock that the intrusion cuts through most recently would be the youngest.

So, the sedimentary rock layer that is immediately above the igneous intrusion would be the youngest rock layer.

To determine which rock is the youngest in this scenario, you need to understand the principles of relative dating in geology. Relative dating involves determining the order of events or objects based on their position within the rock record.

In this case, the igneous intrusion, which is an igneous rock that has penetrated the sedimentary layers, is younger than the rocks it has intruded upon. This is because igneous rocks form when molten material (magma) cools and solidifies, which means the intrusion must have occurred after the sedimentary rocks were already in place.

Therefore, the youngest rock would be the one immediately adjacent to the igneous intrusion. This rock would have been formed before the intrusion but after the deposition of the older sedimentary layers it cuts through. The two sedimentary rocks below the intrusion would be older.

So, to answer your question, the sedimentary rock adjacent to the igneous intrusion is the youngest in this scenario.