When viewing the image of Sam's backyard, we can see the occurrence of chemical and physical weathering. Physical weathering is caused by the impact of water on rocks, which promotes the breakdown of rock particles. The chemical weathering is also caused by the water that I contact with the rock react with its elements causing chemical reactions that modify the rock.
Regarding erosion, we can consider the erosion by gravity that is common in mountainous regions, like the one shown in the photo. This type of erosion promotes the loss of mass of the rock due to the detachment and rolling of rock particles, due to gravity. We can also notice the rain erosion, created by the impact of water on the rock that detaches the fragments and transports them to other places.
Index fossils represents the fossils of the organisms that lived in a particular geological time zone. The index fossils defines a geological time of a dead organisms. Index fossil ensures that a correct order of geological time appears in a fossil record. The index fossils of organisms that lived for a short period, were abundant and widespread geographically.
When the moths camouflage with their surroundings, they are less likely going to be eaten by their predators. So therefore, more moths are going to want to mate with the darker moths that blend with their surroundings.