Cao Tan, a researcher from the Heritage Section of the provincial Department of Culture, Sports and Tourism, said an excavation discovered a layer of red sediment containing animal bones and the shells of fresh-water molluscs such as mountain and stream snails. 

They show the presence of human beings living in the cave in the late Pleitocene period, more than 10,000 years ago, said Mr Tan. 

The findings included assorted shells of marine molluscs such as barnacles and oysters dating back 5,000 to 7,000 years. 

Based on this, archaeologists have surmised that the Son Cave since may have served as a shelter for prehistoric humans in a different living environment during two stages of history. 

The Son cave is located within the historic site of the ancient capital of Hoa Lu under King Dinh Tien Hoang, the founder of the second Vietnamese dynasty, from 968-979.

VNA