Earlier hominids had been using stone tools for 3.4 million years, but the use of grinding to sharpen stone tool edges didn't come until much later, after Homo sapiens evolved, researchers said.
Previously the oldest ground tools, dated to 22,000 to 30,000 years ago, were found in northern Australia and Japan.
The ground-edge ax was uncovered in May 2010 at Nawarla Gabarnmang, a site famous for Aboriginal rock art that is 25 miles from the quarry where the rock was sourced, the researchers report in the journal Australian Archaeology.
Before humans learned to grind edges on their tools, axes were less efficient at cutting wood, said David Bruno, a Monash University archaeologist and a member of the team that made the discovery.
"In this sense edge grinding is a significant technological innovation that increases the efficiency of the tool," Bruno told LiveScience.com. "It is a technological innovation on par with the invention of the bow and arrow."