Scientists theorize that the continents move across the surface of the Earth on plates. The places where these plates meet are often the sites of geological events such as volcanoes, earthquakes, and mountain ranges. In the Atlantic Ocean, an underwater mountain range known as the Mid-Atlantic Ridge has formed at the boundary between two plates. Hot magma breaks through the top of the ridge and hardens to form oceanic crust. In the Pacific Ocean, a boundary between two plates has created a trench. Oceanic crust slips into this trench and melts back into the Earth. Scientists theorize that the continents move across the surface of the Earth on plates. The places where these plates meet are often the sites of geological events such as volcanoes, earthquakes, and mountain ranges. In the Atlantic Ocean, an underwater mountain range known as the Mid-Atlantic Ridge has formed at the boundary between two plates. Hot magma breaks through the top of the ridge and hardens to form oceanic crust. In the Pacific Ocean, a boundary between two plates has created a trench. Oceanic crust slips into this trench and melts back into the Earth. Some scientists theorize that Earth's crust is formed at ocean ridges and recycled within the Earth at ocean trenches. Which of the following is the BEST supporting evidence for this theory?