Archaeologist Mike Hermes found an ancient coin lying on a beach last year in the Wessel Islands, which are part of the Northern Territory.
The Kilwa coin from more than 10,000km away here in Tanzania, dates from before the 15th century when European explorers reached various parts of the world, including Africa.
Its surface is eroded, obscuring identifying features, but Hermes is confident.
“We’ve weighed and measured it, and it’s pretty much a dead ringer for a Kilwa coin,” he said at the weekend, adding: “Well, that could change everything.”
In 1944, five coins were found in the Wessel Islands that were later proven to be 1000-year-old Kilwa coins, opening up the possibility that sailors from distant countries landed in Australia much earlier than thought.
During World War II the Wessel Islands — an uninhabited group of islands off Australia’s north coast — were an important place for defending the mainland from attack.
Australian soldier Maurie Isenberg was stationed on one of the islands to operate a radar station and spent his spare time fishing on the beaches.
While sitting in the sand with his fishing rod, he discovered a handful of coins in the sand.
He didn’t have a clue where they came from but pocketed them anyway and later placed them in a tin.
In 1979 he rediscovered his “treasure” and decided to send the coins to a museum to get them identified.
The coins proved to be 1000 years old.
Aboriginal Australians are thought to have first arrived on the mainland by boat from the Malay Archipelago between 40,000 and 60,000 years ago.
Captain James Cook declared Australia “terra nullius” (empty land) and claimed it for the UK in 1770.
But Captain Cook wasn’t the first European to step on Australia’s shores.
In 1606, a Dutch explorer named Willem Janszoon reached the Cape York Peninsula in Queensland, followed a few years later by another Dutchman Dirk Hartog.
According to a team of Australian and US historians, archaeologists, geomorphologists and Aboriginal rangers, the five coins found in 1944 date back to the 900s to 1300s.
They are from the former Kilwa sultanate, now a World Heritage historical site in Kilwa district, Lindi region.
Kilwa once was a wealthy trade port with links to India in the 1200s to 1500s.
The trade with gold, silver, pearls, perfumes, Arabian stoneware, Persian ceramics and Chinese porcelain made the city one of the most influential towns in East Africa at the time.
The copper coins were the first coins ever produced in sub-Saharan Africa, and have only twice been found outside Africa: once in Oman and the Australian find in 1944.
Archaeologists have long suspected there may have been early sea trading routes that linked East Africa, Arabia, India and the Spice Islands even 1000 years ago.