What is known about Adam's Bridge between India and Sri Lanka, and why does it still matter?
Short answerIt is a very shallow limestone formation that large ships avoid, with uncertainty in this answer about when it became permanently submerged.
NotesAdam's Bridge, also known as Rama's Bridge, lies between India and Sri Lanka. Its shallow limestone formation obstructs navigation even where the former land connection is underwater. Large ships therefore avoid the passage. The date when it became permanently submerged remains uncertain in this initial answer.