The killers rolled slowly down the narrow alley, three men jammed onto a single motorcycle. It was a little after 11 am on July 31, 2013, the sun beating down on the low, modest residential buildings lining a back street in the Indian farming village of Raipur Khadar. Faint smells of cooking spices, dust, and sewage seasoned the air. The men stopped the bike in front of the orange door of a two-story brick-and-plaster house. Two of them dismounted, eased open the unlocked door, and slipped into the darkened bedroom on the other side. White kerchiefs covered their lower faces. One of them carried a pistol.

Inside the bedroom Paleram Chauhan, a 52-year-old farmer, was napping after an early lunch. In the next room, his wife and daughter-in-law were cleaning up while Paleram's son played with his 3-year-old nephew.

Gunshots thundered through the house. Preeti Chauhan, Paleram's daughter-in-law, rushed into Paleram's room, Ravindra, right behind her. Through the open door, they saw the killers jump back on their bike and roar away.

Paleram lay on his bed, blood bubbling out of his stomach, neck, and head. "He was trying to speak, but he couldn't," Preeti says, her voice breaking with tears. Ravindra borrowed a neighbor's car and rushed his father to a hospital, but it was too late. Paleram was dead on arrival.

Despite the masks, the family had no doubts about who was behind the killing. For 10 years Paleram had been campaigning to get local authorities to shut down a powerful gang of criminals headquartered in Raipur Khadar. The "mafia," as people called them, had for years been robbing the village of a coveted natural resource, one of the most sought-after commodities of the 21st century: sand.

That's right. Paleram Chauhan was killed over sand. And he wasn’t the first, or the last.

Our civilization is literally built on sand. People have used it for construction since at least the time of the ancient Egyptians. In the 15th century, an Italian artisan figured out how to turn sand into transparent glass, which made possible the microscopes, telescopes, and other technologies that helped drive the Renaissance's scientific revolution (also, affordable windows). Sand of various kinds is an essential ingredient in detergents, cosmetics, toothpaste, solar panels, silicon chips, and especially buildings; every concrete structure is basically tons of sand and gravel glued together with cement.