Final answer:
At a divergent plate boundary like a mid-ocean ridge, one should expect the formation of new ocean floor through volcanic activity, creation of basaltic lava, formation of underwater mountain ranges, and volcanic eruptions that bring material from the Earth's mantle to the surface.
Step-by-step explanation:
At a divergent plate boundary such as a mid-ocean ridge, you should expect to find new ocean floor being formed as a result of volcanic activity. This involves molten rock, or basaltic lava, rising from below to fill the space between the receding plates, which forms a new crust. This basaltic lava is a type of igneous rock that constitutes most ocean basins. Besides the creation of new seafloor, one can also observe underwater mountain ranges like the Mid-Atlantic Ridge, which is a hallmark of such divergent zones.
Not only does this process form new igneous rock, it also provides material for volcanoes at the mid-ocean ridges. Volcanic activity at these locations is a significant way to sample material from deeper within Earth’s mantle. Additionally, the pattern of magnetic reversals found in rocks near mid-ocean ridges sheds light on the history of Earth’s magnetic field and can be used to estimate the rate of seafloor spreading.