Complex sentence: The Holocene Impact Working Group think that it was created about 5,000 years ago during the Holocene epoch when a comet impacted in the ocean, and that enormous megatsunamis created the dune formations which later allowed the crater to be pin-pointed.
Split into simpler sentences: The Holocene Impact Working Group think that the crater was created about 5,000 years ago during the Holocene epoch when a comet impacted in the ocean. Enormous megatsunamis created the dune formations which later allowed the crater to be pin-pointed.