Chinese and American fossil hunters say stone implements discovered in northern China are the earliest evidence of human habitation in eastern Asia.

The tools are around 1.36 million years old, which also indicates early man ventured farther north earlier than previously thought, they report in the British scientific journal Nature.

The artifacts comprise scrapers and borers found in the Nihenwan Basin, near the Sanggan River in northern China, an area of thick lake silt that has been a treasure trove of mammal fossils.

A team from Chinese Academy of Sciences, the Smithsonian Institution in Washington and California Polytechnic State University carried out a dating analysis of the soils.

Their principal technique was magnetostratigraphy, which is based on the idea that the Earth's magnetic field changes directions at irregular intervals.

It is possible to date the strata of ancient geological deposits, such as lava and mud, according to the magnetic field that prevailed when the layer solidified.

The Nihenwan Basin lies on the latitude of 40 degrees north, which suggests that Homo erectus -- an early forebear of modern Man -- was quite resilient and able to withstanding climate change.

At the time, the world's climate was going through a cycle of variability, in which northern China suffered spells of aridity.

(China Daily 09/28/2001)