Atoll remains of an ancient atoll as a hill in a limestone area is called a reef knoll. The second largest atoll by dry land area is Aldabra with 155 km². The largest atoll in terms of island numbers is Huvadhu Atoll in the south of the Maldives with 255 islands. In 1842, Charles Darwin explained the creation of coral atolls in the southern Pacific Ocean based upon observations made during a five-year voyage aboard from 1831 to 1836. Accepted as basically correct, his explanation involved considering that several tropical island types—from high volcanic island, through barrier reef island, to atoll—represented
Palmyra Atoll the north, followed by Kaula Island in the south. The northern arch of islets is formed by Strawn Island, Cooper Island (or Cooper-Meng Island since former Cooper and Meng Islands were joined in 1940), Aviation Island, Quail Island, Whippoorwill Island, followed in the east by Eastern Island, Papala Island and Pelican Island, and in the south by Bird Island, Holei Island, Engineer Island, Tanager Island, Marine Island, Kaula Island, Paradise Island, the Home Islets and Sand Island (clockwise). Palmyra Atoll is in the Samoa Time Zone (UTC−11:00), the same time zone as American Samoa, Midway Atoll, Kingman Reef and Jarvis