The bank covers an area of , and is composed of two separate structures, the smaller North Bank (also called Ritchie Bank), and the huge South Bank. If the South Bank were recognized as a submerged atoll structure, it would be the largest of the world, almost three times the size of the Great Chagos Bank, commonly considered the largest atoll structure of the world. Even smaller North Bank would be one of the largest atolls worldwide. The North Bank and the South Bank appear to have different origins, since they are separated by a fault. The South Bank and the Great Chagos Bank were one single feature until about 64 to 69 million years ago, when an ocean ridge opened between them and started pushing them apart.