Gilbert and Ellice Islands atolls and coral islands in the western Pacific Ocean that are recognised as part of the Micronesia subregion of Oceania. The Gilbert Islands are the main part of what is now Republic of Kiribati ("Kiribati" is the Gilbertese rendition of "Gilberts") The atolls and islands of the Gilbert Islands are arranged in an approximate north-to-south line. In a geographical sense, the equator serves as the dividing line between the northern Gilbert Islands and the southern Gilbert Islands. The Ellice Islands are south of the Gilbert Islands. The Ellice Islands comprises three reef islands and six true atolls spread out between
Geology of the Pacific Ocean . The Pacific Ocean developed from the Panthalassa, a vast global ocean, following the breakup of the supercontinent Pangaea in the Mesozoic Era, gradually forming Gondwana and Laurasia, which in turn divided. There is no firm date for when the changeover occurred, as the replacement of the sea bed is a continuous process, though reconstruction maps often change the name from Panthalassic to Pacific around the time the Atlantic Ocean began to open. The Panthalassic Ocean first opened around 750 million years ago at the breakup of Rodinia, but the oldest Pacific Ocean floor is only around 180 Ma old.