ASBOG Practice Exam

What does the law of original horizontality emphasize?

1. The relationship between rock types

2. The original orientation of sediment layers

3. The effects of erosion

4. The processes of sedimentation

The correct answer is: The original orientation of sediment layers

The law of original horizontality emphasizes that sedimentary rocks are initially deposited in horizontal layers due to the influence of gravity. This principle, first formulated by Nicolaus Steno in the 17th century, suggests that unless disturbed by geological events, such as folding or faulting, sediment layers will remain relatively flat and parallel to the Earth's surface. Understanding this law is crucial in geology, as it provides a foundational concept for interpreting the geological history of an area. When geologists observe sedimentary rock layers, they can infer that any deviations from horizontal alignment are results of later geological processes, such as tectonic activity or erosion. This principle serves as a starting point for sedimentology and stratigraphy, allowing geologists to reconstruct past environments and depositional settings. By recognizing that sediment was originally laid down in a horizontal manner, scientists can better understand the chronological sequence of geological events and the dynamic processes that affect rock formations over time.