This ordinary-looking piece of aluminium could actually be proof that aliens are real and have visited Earth, according to experts.

The piece of metallic aluminium is estimated to be around 250,000 years old - a long time before mankind ever started producing it.

Builders found the 20cm-long chunk on the shores of the Mures River in Aiud, Romania, about 33 feet underground in 1973, with the details only just surfacing.

Archeologists enlisted to study the aluminium initially thought it might be the end of an ace, but further study found it was an extremely lightweight metal that had been manufactured.

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Mystery: The object predates when mankind produced aluminium (CEN)

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Tests showed that the object is made of 12 metals, 90% aluminium, and it was dated by Romanian officials as being 250,000 years old.

More experts brought in to conduct tests said the dates were far later, ranging between 400 and 80,000 years old - but even at 400 years old it would still be 200 years earlier than when aluminium was first produced.

The object has concavities that suggest that it was part of a more complex mechanical system - and possibly alien in origin.

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Discovery: Experts are still puzzled as to the origin of the chunk of metal (CEN)

Gheorghe Cohal, the Deputy Director of the Romanian Ufologists Association, told local media: “Lab tests concluded it is an old UFO fragment given that the substances it comprises cannot be combined with technology available on Earth.”

Local historian Mihai Wittenberger has tried to claim that the object is actually a metal piece from a World War II German aircraft - but this does not explain the age of the artefact.

The metal object has now gone on display in the History Museum of Cluj-Napoca with a sign alongside that reads “origin still unknown”.

Top pic: CEN