China on Wednesday began a rescue excavation in Zhoukoudian Caves in a suburb of Beijing, where the skulls of "Peking Man," or Homo erectus, were found in the 1920s and 1930s.

Paleoanthropologists will excavate 20 square meters along the western wall of Locality 1, said Gao Xing, deputy director and research fellow of the Chinese Academy of Sciences (CAS) Institute of Vertebrate Paleontology and Palaeoanthropology (IVPP), at a press conference on Wednesday.

Locality 1, where the first complete skull of "Peking Man" was found, used to be a 20-meter-wide, 140-meter-deep cave but the ceiling has collapsed.

The four-month excavation aims to protect the western wall from threats of collapse, he said. "We found a wide longitudinal crack from the top and rocks in the wall are loose. It could collapse in any moment. Once it collapses, it will cause serious damage to the relic deposit in the cave."

This section remained the most complete sequence of stratum settlement with rich relic deposits of great significance, he added.

Scientists will first work on the crack areas over the next month and on the whole section between August and October.

In addition to the excavation, paleoanthropologists will try to reinforce the cave wall and install more detailed introductions for visitors.

Paleoanthropologists began preparing for the evacuation in May. They have mapped the section with laser 3-dimension scanning technology, which offered reliable data for the excavation, Gao said.

"Peking Man," the tool-making "erect man," was previously believed to have lived in Zhoukoudian Caves about 400,000 to 500,000 years ago. But in March Chinese scientists revealed that using a new radioactive dating method, they found they were actually 200,000 years older.

Chinese Archaeologist Pei Wenzhong found the first complete skull in December 1929, together with a large number of stone tools and evidence of fire used by humans.

In 1936, technician Jia Lanpo, who later became an archaeologist, unearthed three skulls.

Fossils unearthed in the caves were found to belong to 40 individuals, with more than 100,000 stone tools. Large scale excavation ceased in 1937 when the Japanese army invaded China.

Paleoanthropologists carried out several small-scale excavations over the past 72 years but never a project of this scale, Gao said.

Zhoukoudian Caves was listed by UNESCO as a World Heritage site in December 1987.

China had reinforced the other 13 caves in Zhoukoudian between 2004 and 2006 at a cost of 5.5 million yuan (US$797,000),but not including Locality 1.

(Xinhua News Agency June 24, 2009)