Final answer:
The largest ocean on Earth is the Pacific Ocean. Oceanic crust is subducted and recycled into the mantle, and regions where continents have collided may be termed 'suture zones' due to the presence of ophiolites. So, the correct answer is option a.
Step-by-step explanation:
The ocean basins have indeed seen significant changes over Earth's geological history. At present, the largest ocean on Earth is the Pacific Ocean. This is followed by the Atlantic Ocean, the Indian Ocean, and the Southern Ocean.
The Southern Ocean, interestingly, doesn't border a land mass at its northern boundary; instead, it meets the Atlantic, Pacific, and Indian Oceans near the 60° latitude. Over time, due to tectonic plate movements, ocean basins expand and contract and new ones can form, such as with the breakup of Pangea and the formation of the Atlantic Ocean.
The oceanic crust that once existed between continental tectonic plates is typically subducted and recycled back into the mantle. Ophiolites, which are sections of the Earth's oceanic crust and the underlying upper mantle that have been uplifted and exposed above sea level, serve as evidence of past ocean basins.
Some geoscientists suggest using the term 'suture zone' for regions where continents have collided and ophiolites can be found, such as in the Himalayan Mountains, signifying where two land masses have joined together.