Halong Bay has experienced at least 500 million years in various geological states of orogeny, marine transgression and marine regression. During the Ordovician and Silurian periods (500-410 million years ago), Halong Bay was deep sea. During the Carboniferous and Permian periods (340-250 million years ago), it was at shallow sea level. The present landscape of sea-islands was formed around 7 or 8 thousand years ago by the sea invasion during Holocene transgression.
Particularly about 11,000 years ago, Cat Ba – Halong area has began to develop ancient cultures such as the Soi Nhu and Halong cultures. Many artifacts and antiques have been found such as rock tools, stone jewelries, ceramic products, harvesting and hunting kit, fishing tools, copper arrows etc – all dated from different periods in ancient time.
