What are two ways rock layers can change after they are deposited horizontally?

The answer is unconformity and folded

Sedimentary rocks is deposited in flat layers. Over years, the sediment becomes deeply buried, hardens, and changes into sedimentary rock. At the same time, remains of organisms in the sediment may become fossils ... According to the law of superposition, in horizontal sedimentary rock layers the oldest is at the bottom.