Study GuideGeology–Geologic Structures1. InterpreƟng StructuresUnderstanding how geologic structures form helps scientists piece together thegeologic historyof aregion. In simple terms, the more structures we see in an area, the more complicated its history islikely to be. These structures can shift, break, or bury blocks of bedrock, which makes interpreting therock record more challenging—but also more interesting.Geologic structures are important for more than just classroom study. They play a major role inreal-world applications. For example, engineers and geologists need to understand structural historywhen searching forpetroleum and metallic ores. The same knowledge is also critical when decidingwhere to build large structures likedams or nuclear reactors, which must be placed on stablebedrock.1.1 Using Rock Movement to Understand the PastGeologists often figure out structural events by looking athow rocks have moved. One key idea theyuse is thelaw of original horizontality. This law states that sedimentary rocks are originallydeposited in flat, horizontal layers.•If sedimentary layers are still flat today, it suggests that the rockswere lifted upwardevenly by tectonic forces.•If the layers are tilted, it means the uplift was uneven. One side experienced more stressthan the other, causing the layers to lean in one direction.1.2 When Rock Layers Are Upside DownSometimes, things get even more surprising. In rare cases, sedimentary layers appear horizontal, butfossils and age relationshipsshow that the top layer is actually theoldest. Normally, older layersare found at the bottom. When this order is reversed, it tells us that powerful tectonic forces haveoverturned the entire sequence of rocks. What was once the bottom layer is now on top.Preview Mode
This document has 18 pages. Sign in to access the full document!