Cape Town: A group of prehistoric people mastered a difficult and delicate process to sharpen stones into spears and knives at least 75,000 years ago, more than 50,000 years earlier than previously thought, according to a report.

This technique, known as pressure flaking, allowed for the more precise shaping of stones to turn them into better weapons for hunting, a paper published yesterday in the US periodical Science said.

"These points are very thin, sharp and narrow and possibly penetrated the bodies of animals better than that of other tools," said Paola Villa, a curator at the University of Colorado Museum of Natural History and a study co-author. The earliest evidence of pressure flaking was from the Upper Paleolithic Solutrean culture roughly 20,000 years ago.