It has been almost 80 years since she vanished, and still they are trying to find her.

Amelia Earhart was on her way to becoming the first woman pilot to circumnavigate the globe when she and the navigator, Fred Noonan, set off from Lae, New Guinea, in a Lockheed Electra twin-engine airplane on July 2, 1937.

But something went wrong en route to Howland Island in the central Pacific Ocean, and both of them seemed to vanish.

It was sensational news at the time. Earhart, then 37, was known not only as an accomplished pilot but also as a writer, a speaker and even a fashion designer during the 1930s, when it was still politically correct to refer to her as an aviatrix.

Today, some people insist that traces of the pilot have been found and that they are growing closer to proving a disputed theory about her disappearance. To that end, a new mission is underway. Researchers are now cruising toward Nikumaroro, a coral atoll that is part of the Phoenix Islands of Kiribati. With them are four dogs adept at sniffing out human remains — even decades-old remains that may be several feet underground.

The canines are an exciting a new twist, but the context is sobering: This is just one more expedition in a search that has spanned decades, costing millions of dollars and sparking serious rivalries among researchers.

This mission, which set off from Fiji on Saturday, is a collaboration between National Geographic, the tour company Betchart Expeditions and The International Group for Historic Aircraft Recovery, a nonprofit organization based in Pennsylvania. It is better known by its acronym TIGHAR, which is pronounced “tiger.”

TIGHAR has been at this for decades. This will be its 12th expedition to Nikumaroro.

“It’s been a long process. It’s like building a jigsaw puzzle,” said Ric Gillespie, the organization’s executive director. He sees his past 11 trips not as a string of failures, but as a slow and steady accumulation of evidence that will lead him, one day, to the smoking gun he’s looking for.

National Geographic has sponsored the four forensic canines — Berkeley, Piper, Marcy and Kayle, all Border collies — but it would not share details about the cost of this week’s expedition. Gillespie said that TIGHAR’s own expeditions in past years, which were funded mostly through member contributions, have cost anywhere from $500,000 to around $2 million.

Andrew McKenna, a diver who is a member of TIGHAR, said in a phone interview from Fiji last week that he would be looking for the Electra at sea, while the dogs do their work on land.

Their stay on the remote atoll of Nikumaroro will last for eight days, he said. And even though the island is very hot, covered in thick vegetation and populated by massive coconut crabs, he was already wishing for more time. “Frankly,” he said, “you always leave just when you were beginning to feel productive.”

According to TIGHAR’s hypothesis, Earhart and Noonan veered south of their planned flight path and landed on Nikumaroro (then referred to as Gardner Island). They sent out distress signals using power from the Electra’s engine, until a high tide washed the plane away. Navy planes then flew over the island in their search for the Electra and, not seeing it, passed by.

“The drama really is in that moment,” McKenna said. “You just imagine Amelia waving her arms frantically at the airplanes overhead, and then they fly away, and she’s literally marooned. What do you do then?”

But not everyone agrees with that version of events.

Some have argued in support of more outlandish ideas, claiming that Earhart was a spy who was captured by Japanese operatives. There was also a theory that she somehow made her way back to the United States and lived a long, quiet life under a different name in New Jersey.

But historically, the most widely accepted idea has been the so-called crash-and-sink theory — the one originally endorsed by the U.S. government — which holds that Earhart’s plane plunged straight into the ocean.

The incompatibility between the Nikumaroro narrative and the crash-and-sink hypothesis sparked a decades-long rivalry between opposing teams of researchers and historians. Books and articles have been written, harsh words have been exchanged, and expensive expeditions have been launched in support of both major theories.

“They just want to believe it so desperately, that we can find her,” said Dorothy Cochrane, a curator in the aeronautics department at the Smithsonian National Air and Space Museum. “I hope we find her some day, but it’s not that important to me. What’s important to me is her legacy.”

Cochrane said she believes with near-certainty that Earhart never reached Nikumaroro.

Gillespie said there are various other hints in support of his theory, citing documents of radio transmissions, records of bones found on the island, an old photo that appeared to show the Electra poking out of the water near the atoll in 1937, and more. It’s all been carefully documented on the TIGHAR website.

But evidence, he said, is not proof.

“What the public wants is a smoking gun,” he said, adding that if the Electra can’t be found, “they want a bone with DNA that matches Earhart’s DNA.”

That is what the dogs are for.

Still, Gillespie has his doubts as to whether these dogs would be able to uncover usable DNA samples after 80 years.

And his critics have doubts as to whether Earhart ever made it to the atoll at all.