Carter, a dark-haired, sharp-featured 42-year-old expat rancher from Texas, is wearing Wranglers and a 2006 Longhorns Rose Bowl Championship cap. Since flying down from the U.S. in his own plane in 1996, the former elite Army soldier has logged more than 500,000 nautical miles, slowly building, with his wife, a small empire of conservation-oriented enterprises, including their own 11,650-acre sustainable ranch; Brazilian Adventure Travel, an ecotourism company that empowers locals; and Aliança da Terra, a nonprofit that offers market-based incentives to ranchers and farmers. But Carter's most pressing project right now is to match Lutz's high-profile property with a wealthy American buyer who will prove that ranching and conservation really can coexist.

At the moment, he's sitting on the tile veranda, his boots in the sand, drinking a Skol beer, dipping Copenhagen, and speaking in a deep, clear twang perfected in San Antonio, where he grew up. The man who is possibly the future of Amazonian conservation could almost be mistaken for a redneck.

David Johnson, 55, tall, blond, and mustached, is on the couch with his wife, Suzie, 64, a petite former tennis instructor turned ranch hand and expert horsewoman. The couple live in Bozeman, Montana, where Johnson works as a broker for Hall & Hall, the U.S.'s largest resource-management firm dealing with high-end rural real estate. Its clients have put more private property under conservation easement than almost any other brokerage firm in the U.S. Johnson is here to size up Fazenda Santo Antonio so that he can market it to a database of 25,000 potential buyers—moguls like Ted Turner, who bought most of his western holdings from Hall & Hall. Turner's not interested, but for months Carter and Hall & Hall have been courting billionaire CEOs and iconic celebrities.

"We've seen less than a hundredth of this place," says Johnson, taking a sip of beer. "But you just breathe the air here and it's overwhelming."

An hour ago, Carter fired up his Cessna to take us on a sunset cruise, showing us what would be lost if the ranch were sold off for more intensive agriculture.

"All that, that, that, and that would be cleared," Carter shouted over the engine, pointing to a ridgetop still lush with native canopy forest.

The ranch balances precariously between the world's largest wetlands—the 68,000-square-mile Pantanal—and the world's largest soybean farm. While the property supports a herd of 23,000 grass-fed cattle and 7,500 acres of tilled soybean fields, 89 percent of it has been meticulously maintained in its original state, making it an island oasis for more than 420 bird species, two recently discovered insect species, and some of the most diverse wildlife in Brazil. On a Carter-led high-speed jeep safari, we found a poisonous jararaca snake, a giant anteater vacuuming out a termite mound, and a hard-charging herd of white-lipped peccaries. Beyond the lazing caimans, jabiru storks, roseate spoonbills, buff-necked ibises, jacana birds, and great egrets, Carter spotted a 400-pound tapir grazing a football field away.

"How did you see that?" I asked.

"Ah, you know," he said. "I'm always looking out for the enemy."