Written by Jessie Yeung, CNN

On a desert plateau 36 miles from the tiny South Australian town of Marree lies one of the country's greatest unsolved modern mysteries.

Lines run through the barren earth, carved one foot deep and over 115 feet wide. Stretching over 2.6 miles, the lines join together to form an image of an Aboriginal figure wielding a stick or boomerang.

This is the Marree Man, one of the world's largest geoglyphs. In the 20 years since it first appeared in 1998, nobody has stepped forward to claim responsibility, giving rise to countless theories and investigations.

Now, an Australian entrepreneur is offering $3,712 ($5,000 AUD) for information regarding its creation.

Entrepreneur Dick Smith at a 2017 press conference in Sydney, Australia. Credit: Mark Kolbe

Dick Smith, founder of Dick Smith Electronics and Dick Smith Foods, decided to tackle the mystery in 2016.

In the last two years, he and his team have pored over images and videos, investigated the various theories, and reviewed the few pieces of evidence available -- to no avail.

He believes a group was responsible, and is now hoping that a sizable cash award will help bring forward new information.

"I can't see how it was done by one person, you'd have to have three or four to do it, and it would take weeks to put in. In that case, how has it been kept secret for 20 years?"

American origins?

The most popular theory is that an American (or a group of Americans) were behind the geoglyph.

Immediately after it was discovered, a series of press releases were anonymously faxed to the Marree Hotel and to newspaper The Advertiser, describing "the world's largest work of art." However, people quickly noticed that the writing used American spelling and language, including the use of miles instead of kilometers.

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More evidence emerged pointing to an American creator, including a buried plaque bearing the image of an American flag and the Olympic rings.

However, many Australians, including Smith, believe these clues to be red herrings.

An alternative theory credits Aboriginal artist Bardius Goldberg with the work. Goldberg, who lived in Alice Springs, had apparently told friends he was responsible for the Marree Man. However, this was never confirmed, and Goldberg died in 2002.

Some have theorized that it was done by the Australian army. Others yet insist it was the US Air Force, leaving a parting gift after they left Woomera in the late 1990s.

The harsh desert environment took its toll on the Marree Man, and with little maintenance, its lines began fading. However, locals plowed the lines back in 2016, keeping the Man and the mystery alive.