100 meters — without human intervention.Indeed, up and down, over and over, if you believe the fossil records and modern science.
No doubt about that. Sea levels have changed considerably over time (and at geological rates) in paleohistory. They had to, when a lot of water was locked up in continental ice caps. As for highstands, all the phosphate deposits in Florida were created when most of Florida was underwater (for a considerable time), and the limestone underlying Florida is also a marine formation.
But human activities are helping the process along right now.