1. Based on the theory of plate tectonics, you would not expect to find very old rock or very old soil in an oceanic ridge because oceanic ridges are formed at divergent boundaries where new oceanic crust is continuously created as magma rises and solidifies. This means the rock at the ridge is always newly formed, making it geologically young.
2. Based on the theory of plate tectonics, you would expect to find very new rock or very old rock in an oceanic trench because oceanic trenches form at convergent boundaries where one oceanic plate is subducted beneath another. The rock being subducted is typically older oceanic crust that has moved away from its origin at a mid-ocean ridge over millions of years, so the trench contains some of the oldest oceanic rock on Earth.
3. The Mariana Trench is located at a convergent boundary where the Pacific Plate (oceanic) is being subducted beneath the Mariana Plate (also oceanic). As the Pacific Plate moves westward, it collides with the Mariana Plate, forcing the denser Pacific Plate downward into the mantle. This subduction process creates the deep Mariana Trench, which is the deepest known point in Earth’s oceans.
Parent Tip: Review the logic above to help your child master the concept of plate boundaries worksheet answers.
