Complex sentence: The existence of an offshore field was suspected for a long time, largely due to the persistent natural seepage of oil from the sea floor; the area around Coal Oil Point is now one of the most actively studied seep zones in the world.
Split into simpler sentences: The existence of an offshore field was suspected for a long time, largely due to the persistent natural seepage of oil from the sea floor. The area around Coal Oil Point is now one of the most actively studied seep zones in the world.