Science Olympiad Dynamic Planet Practice Test 2026 – Your Comprehensive Guide to Success!

The correct answer is tension, which refers to the type of stress that acts to stretch a material. When rocks experience tension, the forces exerted on them pull away from each other, leading to elongation and thinning, particularly in the middle of the rock. This can result in features such as valleys and rift zones, which are indicative of extensional environments.

In contrast, compression involves forces that push materials together, often resulting in thickening and folding rather than thinning. Shearing stress occurs when forces slide past one another, which can lead to lateral displacement but not necessarily thinning of materials. Normal stress, while it can involve tension or compression depending on the orientation of the stress, does not specifically describe the stretching action that causes thinning in the middle of rock. Thus, in the context of the question, tension is the most accurate description of the type of stress that stretches rock.