ASBOG Practice Exam

Both the law of superposition and the law of horizontality explain the original placement of which types of rocks?

1. Metamorphic rocks

2. Intrusive igneous rocks

3. Sedimentary or extrusive igneous rocks

4. Volcanic rocks

The correct answer is: Sedimentary or extrusive igneous rocks

The law of superposition states that in an undeformed sequence of sedimentary rocks, the oldest layers are at the bottom, and the younger layers are on top. The law of original horizontality states that layers of sediment are originally deposited horizontally under the action of gravity. Together, these laws help explain the deposition and arrangement of sedimentary rocks. Sedimentary rocks are formed from the accumulation of sediment, which can be derived from the weathering and erosion of pre-existing rocks or from biological processes. As sediment layers settle and accumulate over time, the laws guide geologists in interpreting the geological history of an area, including changes in environment and time. While igneous rocks, particularly intrusive ones, form from the cooling and solidification of magma beneath the Earth's surface, their formation is not governed by these laws in the same way as sedimentary layers, which are specifically shaped by deposition. Metamorphic rocks, formed from existing rocks that undergo a metamorphic process due to heat and pressure, also don't directly relate to these deposition laws. Therefore, the combination of these principles primarily applies to sedimentary and extrusive igneous rocks, which are deposited in horizontal layers. Thus, the correct answer highlights that the laws provide crucial insights into understanding sedimentary