The islands of North Carolina's Outer Banks are the children of the sea. A series of low-slung sand islands stretching in a thin line from the Virginia border to Cape Lookout, they were born at the end of the last Ice Age when huge continental glaciers began to melt and the ocean began to rise. Since they formed ten thousand years ago, they have raced the rising waters westward, migrating as much as fifty miles to their present location.

The Outer Banks were formed by the force of moving water and moving water shapes them still. The islands were created when rivers and streams carrying silt- and sand-laden glacier meltwater flowed out into the ocean, creating deltas on either side of their main channels. These deposits grew as more silt and sand built up the upstream side. The ocean added sand as it washed over the top of the sandbar during high tides and storms. Steady winds blew sand that accumulated even more. A small, shallow lagoon began to form on the west side and a pair of young islands slowly rose out of the sea.

As they grew, prevailing ocean currents slowly ground away the face of the young islands, transporting sand particles down the line; increasing the material at one end as it robbed the same amount from the other. Gradually, the islands began to elongate, stretching into ribbons riding far out into the water. The island chain was broken in points by inlets, which allowed the water still flowing from mainland rivers to empty into the sea, but the island building process continued, with sand building up on the top of the islands while the ocean pulled away on the front of them.

This combination of replenishment and erosion has allowed the barrier islands to move as fast as they do for as far as they do. The vital supply of sand provided by the ocean overwash ensures the western side of the islands will be growing even as the eastern side is being washed away. The process is called island migration, and it's key to the survival of the barrier island chain.

The current set of barrier islands known as the Outer Banks are only one is a series of similar landforms that have existed along the North Carolina coast in the past two million years. In all, sixteen other sets of barrier islands have moved across the ocean to the mainland shore as, far to the north, glaciers ebbed and flowed across the northern latitudes. Most of these earlier landforms are gone now, absorbed into the low-lying mainland or under the rising sea. But remnants do remain. Lower Currituck county near Powell's Point and Roanoke Island are parts of earlier barrier island chains. A line connecting the two is visible on aerial maps, cut in two by Albemarle Sound, the flooded mouth of the Albemarle River, which flowed through the area during the last Ice Age.

There's other evidence of island migration. All along the ocean beaches of the Outer Banks, oysters -- animals that only live in the brackish waters of the sound -- wash up among the other shells in the surf line. The oyster shells are the remains of animals that lived in the same spot when the island was further to the east and the oysters were alive on the sound floor. Covered with sand carried by ocean overwash, the oysters were slowly buried as the island moved over them. As the island continues sliding slowly towards the south and west, the oysters are revealed. Recent estimates say the average age of the oyster shells found on the beaches of the Outer Banks is about eight thousand years old.

More clues can be found. Along certain sections of the beach, brown dinner-plate sized chunks of debris -- marsh peat -- wash up in loose clusters. Like the oysters, the peat chunks are the remains of the early salt marsh plants that once rimmed the western side of the island. And, like the oysters, they too were covered by the moving island, only to be revealed by the pounding surf. But, unlike the oysters that have long ago lost any of their pearls, the peat chunks can sometimes contain a hidden trophy. Inside some of the chunks are prehistoric potsherds and points from the Native Americans who lived along the shores of the Outer Banks for more than a thousand years. Their traces, like the relict barrier island land forms, oysters shells and peat chunks, are just part of the changing nature of the Outer Banks.