GRE阅读高频机经原文：Mystery of the Anasazi_GRE阅读

GRE阅读高频机经原文：Mystery of the Anasazi

　　The folks in this area had become very, very dependent on crops, like maize, and wild turkeys. Ultimately, I think that system backfired and collapsed on them, she says.

　　But why did the system backfire? Why did the entire population collapse? For a while, archaeologists thought they had the single answer: a great drought.

　　This idea was born from ancient wooden beams found in Mesa Verde ruins, beams whose tree rings captured the exact date and climate conditions of the prehistoric time period. Andrew E. Douglass, the father of tree-ring dating, studied these beams and, in a 1929 National Geographic article evocatively titled The Secret of the Southwest Solved by Talkative Tree-rings, announced that hed cleared up the mystery of the prehistoric migration. The beams, he wrote, showed evidence of a massive drought in the region from 1276 to 1299. Drought can be apocalyptic in the Mesa Verde region -- soil turns to powder, trees hold less moisture than kiln-dried wood -- and this one, it seemed, had led to a mass exodus.

　　Scholars are skeptical of single-factor explanations. Could one drought, no matter how devastating, be enough to depopulate an entire region? But for decades, no one had the hard evidence to challenge the drought theory. Interpretations were kind of all over the board, says Kuckelman. That changed seventeen years ago, thanks to the work of a Ph.D. student named Carla Van West.