Along the coast of Peru, a mysterious civilization sprang up about 5,000 years ago. This was many centuries before the Incan Empire. Yet these people were sophisticated. They cultivated crops and orchards. And they built huge monuments of earth and rock. Archaeologists are trying to prove that an abrupt change of climate created this new culture.
     The culture has no official name yet. It flourished in a series of dry coastal valleys called Norte Chico. The place is desolate and misty - a place of rock and dirt. What drove people to settle here is something archaeologist Jonathan Haas, of the Field Museum in Chicago, has puzzled over for years. He doesn't know exactly why they built the mounds he has discovered in Norte Chico. But he has been working on the problem since he first made some unusual finds eight years ago. "You get down on your hands and knees," he says, "and what you find is little pieces of seashell. And then you go, 'How do I get little pieces of seashell out here? I puzzled and puzzled and puzzled over it, and I finally realized it was the people who were building the mounds who were coming out here, and I bet they were fishermen."
     Fishermen who had come up from the coast about 10 miles away, bringing shellfish. But why? Early Americans — hunters and gatherers — came here to fish and collect mussels and clams. That worked fine until about 3000 BCE, Haas says. "At around 3000, the environment begins to change." Haas suspects that what changed was El Nino, the cycle of warm ocean water and torrential rains that regularly descends on western South America. Some shift in the coupling of the atmosphere and the Pacific Ocean made El Ninos more frequent. Haas doesn't know why it happened, but he believes more frequent El Ninos had a drastic effect on coastal life.
     "They were pushing out the cold-water fish," he says of the new El Ninos, "bringing in warm-water fish, killing off local clams and mussels." The fishing got bad, the weather unpredictable. So people moved inland, to the desert valleys. It was only 10 miles or so, but it might as well have been the moon.
     Porvenir is one of dozens of mounds hidden in the creases of the valleys. It's at least 1,000 years older than other mounds in the New World. The mound is a pile of rubble, 30 feet high and maybe 200 feet across. Originally, it was terraced, with a flat top, and was the product of enormous labor. "You have to think of a large stone birthday cake," Haas says. "And it would have been covered with plaster, and you can have it pink, you can have it light orange." He says the builders would have replastered it regularly, to keep it looking sharp.
     On the mound, there are pits dug by present-day looters. Human bones and trash litter the ground. Haas has found precious little jewelry, and this culture made no pottery. Nor has he found weapons. "This isn't the coolest archaeology in the world in terms of the stuff you find," he says. "There are no beautiful ceramics, no gold masks ... our treasure is trash, residential architecture, and all of a sudden those start bringing together this incredible picture of the origins of civilization in South America." Haas believes a change in climate started all of this. "If you think about going from a hunter-gatherer society to this highly centralized society with an organized religion, it's a pretty dramatic change to take place over a very short period of time," Haas says.
     There is still a lot of work to do to prove that. Haas is taking sediment cores from a nearby lake that should tell him about climate changes 5,000 years ago. He and colleagues in the United States are studying the rings in seashells he has found. The shells should provide evidence of how ocean temperatures changed during that period. "There's a very distinctive Andean pattern that starts here and then spreads and forms the foundation for Andean civilization for the next 5,000 years. It's pretty cool," he says.

Source: NPR (11 February 2008)