How were the oceania formed?

Question

How were the oceania formed?

Answer 1

Some of the islands are known in geologic terms as “continental” islands because they are made up of geologically ancient rock which dates from the folding process which formed the Southeast Asia area. The island group of New Guinea is an example of this type. The remaining islands are either high volcanic islands or low coral atolls. The high islands were formed by volcanic activity, the low islands are composed of coral sand.