The South China Sea has long been widely known for its messy mix of rival territorial claims. Less is understood about its geology and how it formed.

Recently, a group of Chinese scientists returned to the country after collecting data from a depth of more than 4,000 meters in the South China Sea.

"This is the first time for us to record the sea basin from such a deep position. Great findings have already been seen from initial analysis, which will substantially promote the scientific understanding of the deep South China Sea," says marine geophysicist Li Chunfeng from Shanghai-based Tongji University. Li is also the co-chief scientist on the expedition project of the International Ocean Discovery Program, an international marine research collaboration that explores the Earth's history and dynamics using ocean-going research platforms to recover data recorded in seafloor sediments and rocks and to monitor subseafloor environments.

The expedition was designed and conducted by Chinese scientists to determine the age of the South China Sea, and how it was formed.

The international team of 32 scientists from 11 countries and regions, including 12 scientists from China, set sail from Hong Kong on board the research vessel JOIDES Resolution on Jan 28, and pulled ashore at Keelung City in Taiwan on March 30, completing the expedition.

During the two-month mission, the team drilled at five sites in the seabed to collect rock samples of different ages within different magnetic zones of the sea. The deepest drilling site was more than 4,300-meters below the surface.

Scientists will study the drilling samples, which will provide critical information on how the crust and mantle evolved during various stages of basin evolution. So far, there is no definite conclusion, Li says, but based on the initial findings scientists estimate that the age is between 16 to 17 million years.

"Researchers will determine these volcanic rocks' ages and characteristics through geochemical and geophysical analyses," says Lin Jian, a marine geophysicist from the Woods Hole Oceanographic Institution in the United States and the other co-chief scientist on the drilling project.

In addition to getting the direct evidence of when the sea was formed, scientists during the expedition also discovered evidence of periodic great volcano eruptions during the formation of the sea. Large amounts of muddy sediment can help to reveal how the sea has evolved.

Li Chunfeng says a detailed report about this expedition will be published in two months.

This is the second time China has participated in the South China Sea discovery project. The first was in 1999, when scientists cored up to 850 meters of sediment at a site 2,000 to 3,000 meters deep. The work offered new insights in the study of the climatic environment history of the sea.

Chinese scientists have already submitted a proposal to the International Ocean Discovery Program for the third expedition in the South China Sea in early 2016, which will help the research in global warming, disaster alleviation and oil exploitation.

wanghongyi@chinadaily.com.cn