Between 1606 and 1770, European adventurers and explorers made the land that would become Australia their own, imprinting their languages, names and cultures indelibly on the world's most remote inhabited continent.

Willem Jansz, Luis Vaz de Torres, Dirk Hartog, Abel Tasman and, of course, James Cook, all left their mark until, in 1787, the British finally despatched the First Fleet to claim and colonise Cook's New South Wales in the name of the British crown.

So much for accepted history. But what if Australia and its indigenous peoples had in fact been discovered by outsiders centuries before Cook and the others had even been born - and how different might world history have been had it been Arabs, rather than Europeans, who had settled and colonised Australia, as early as 900AD?

This is the extraordinary scenario that has been seized upon by the Australian media, based on feverish speculation surrounding impending fresh archaeological investigation of a small stash of Arabic-minted coins found 70 years ago on an island in northern Australia.

And, although the full story of how those coins came to be in northern Australia has yet to be told, the tale at which they hint speaks intriguingly of a time when it was Arabic and Persian sailors who ruled the ocean waves.

To the surprise of Australian archaeologist Ian McIntosh, professor of anthropology at Indiana University in the United States, his announcement this month of an expedition to visit the site of the find "has gone viral - it's absolutely astonishing".

"I had to call in the Indiana University head of public relations to discuss this, because it was the leading story in Australia and I'm still getting television requests," he says. "Australia is one thing - but Voice of Russia?"

Everyone loves a treasure story, of course, and the university's PR department has hinted at a cave of aboriginal legend, supposedly "close to the beach where [the coins were] found and ... said to be filled with doubloons and weaponry of an ancient era".

"I didn't write that," says Prof McIntosh. "That was a PR person at the university. But I do have a map, and it does have an X on it."

The map was drawn 70 years ago. In 1944, at the height of fears of a Japanese invasion, an Australian soldier, Maurie Isenberg, was stationed in the far north of the windswept Wessell Islands, part of Australia's Northern Territory.

Manning a radar station, he was on the lookout for Japanese aircraft, but what found instead while fishing one day on the shore of Jensen Bay on Marchinbar Island were nine coins, including five that would later turn out to have been minted by a lost Islamic civilisation from the east coast of Africa.

He drew a map to remember where he had found them, took them home and, for the next 30 years, forgot about them.

The story first surfaced in academia in 1979, when Isenberg rediscovered the coins among his possessions and had them assessed by experts. They found he had dug up four coins minted by the Dutch East India Company in the 17th and 18th century - nothing too unusual there - but that alongside them he had scooped up five copper coins from the city state of Kilwa, founded on an island south of Zanzibar, barely a kilometre off the coast of modern-day Tanzania, in about 900AD.

Only one such coin, unearthed during an excavation in Oman, had been found outside east Africa, yet the coins were fated to languish for years in a museum drawer.

During the 1990s, Prof McIntosh, who was pursuing his doctorate on the Wessel Islands, located the site where they had been found, but at the time was unable to raise funding to mount an expedition.

He is now going back with a team from the University of Indiana amid hopes that the myths of Jensen Bay might finally be resolved into historical fact.

Although the coins bear the name in Arabic of a ruling Sultan of Kilwa, it remains unclear whether he was the founding ruler or a later descendant. Depending on which, the coins could be from 900 or 1300AD - but, either way, they were minted much earlier than the first European excursions into the waters of northern Australia.

The origins of Kilwa remain unclear, although it is generally accepted that it was founded by a Persian merchant prince who established a trading base on an island within a natural harbour and safely cut off from warring Swahili tribes on the mainland.

Kilwa thrived for almost 600 years, says Prof McIntosh, as "the most prominent port on the east African coast from about the late 900s right through to the 1300s. It controlled the trade in gold, ivory and slaves out of Zimbabwe, up into Arabia, into Persia and across to India.

"The Swahili ships weren't equipped to go further than [Arabia and India]. They could travel up to Arabia on the Monsoons - these were sewn boats, sewn together by coconut fibre. But once you got to Arabia, and of course to India, those big dhows coming out of there would travel all the way to Tang China and down into the Spice Islands."

Kilwa's end was sudden, complete and at the hands of the Portuguese at the beginning of the 16th century, as described by an officer of the British Royal Navy who visited the island in 1824 as part of an expedition to chart the coast of east Africa.

Captain WFW Owen found what he called "the fallen state of Quiloa ... called by the natives Keelwa ... which at the time of the first arrival of the Portuguese upon the coast, appears to have been one of the most considerable of the Arab possessions, holding sovereignty over Sofala, Mozambique and the intervening ports".

So low had Kilwa fallen, "that even the Imaums of Muskat, who appear ever to have been greedy of dominion over those of their own faith on this coast, did not think it worthy of their notice until the French, about 40 years since, attempted to form a settlement there for the slave trade. Since that period it has been under the control of the Muskat government."

So how did coins, minted in east Africa possibly as early as 900AD, find their way to a beach in northern Australia?

"There's as many theories as there are members of my team," says Prof McIntosh. "And I've got about 15 people."

In Life and Death on the Wessel Islands: The Case of Australia's Mysterious African Coin Cache, shortly to be published in the journal Australian Folklore, Prof McIntosh suggests that while "the argument for the involvement of Kilwa traders and also the Portuguese is quite compelling", his own view is that the Kilwa and Dutch coins were probably brought together as lucky charms or gifts for the natives or by sailors from Makassar in Indonesia, who set out in fleets to harvest sea cucumbers in the waters off northern Australia during the 1700s.

But there is another theory, that the coins may have found their way to northern Australia in an Arab dhow, which quite possibly was wrecked on the Wessel Islands, "a type of barrier, or a great catching mitt, for all the Arafura Sea traffic blown south of their intended course".

The suggestion that Arab traders and explorers might have passed this way so long ago might have been dismissed as fantasy until 1998, when the wreck of an Arab-style dhow was found off the Indonesian island of Belitung - puzzlingly far south of known Arabic-Chinese trade routes and complete with 60,000 items of gold, silver, ceramics and other produce made in Tang Dynasty China and lost during the return journey to Arabia.

The date of the wreck, confirmed by carbon dating, was indisputable: one bowl recovered bore the date of manufacture, July 16, 826AD.

So did Arabs "discover" Australia? For the present, Prof McIntosh will go only this far: "We think that this find is some kind of evidence that northern Australia wasn't as isolated as we have come to see it as, and was somehow implicated in this broader Indian Ocean trade linking southern Africa with the Arabian peninsula and on to India and China."

When Prof McIntosh and his team arrive on Marchinbar Island in mid-July they will have two missions.

"One is to use it as a training exercise for Aboriginal Sea Rangers," he says, "because they are the ones who manage this coastline and we want them to have the knowledge and the skills to identify those things which might be invisible to the untrained eye as they go about their business."

Secondly, and together with the Rangers, the team will walk the site at low tides, "looking for any telltale signs that would warrant a bigger expedition in a second stage". Such signs might include non-indigenous rocks, such as basalt, often used as ballast.

"We've got people looking closely at the Belitung wreck, to see just what was there and what we should be looking for if it is an Arab dhow - as quite a lot of our team think it is."

If they do find a wreck associated with the coins, and if it is the remains of an Arab dhow, it will be only the second such find after the Belitung wreck - and all historical bets regarding the "discovery" of Australia will be off.