2 . The Mysteries of The Maya

Extending south from parts known as Mexico into Central America,     1    .The Maya built impressive palaces and temples and step pyramids. How were they built without the use of wheels, metal tools or even animal power?     2     They applied this understanding to the Maya calendar, which was accurate to within 30 seconds per year.

The fact that Maya society was technologically primitive makes its achievements all the more incredible and mysterious.     3     By 700 AD, Maya civilization was at its peak. Yet, within just a couple of generations, it began to mysteriously decline. The cities were left to be taken back by the jungle.

Why Maya civilization collapsed remains a mystery. A deadly disease? Conflicts between cities?     4     They had turned wetlands into fields for growing grains, and had dug huge canal systems. As their population expanded, yet more land was needed for agriculture and more trees for construction. By changing the landscape in this way, the Maya people unknowingly reduced their ability to deal with natural disasters.

    5     Some recent studies have found that there were far fewer tropical cyclones (热带气旋) than usual between 700 AD and 1000 AD, which is likely to have led to a series of droughts. These droughts would have led to food shortages, conflicts and ultimately, the downfall of the cities.

Whatever the reasons, Maya civilization largely disappeared within the deep jungle. Its once-great cities fell into ruin, leaving various mysteries for later people to solve.

3 . In his first year at Harvard, Manny Medrano made a big breakthrough. With the help of his professor Gary Urton. Medrano interpreted a set of six khipus, knotted cora (打结的绳子)used for record keeping in the Inca Empire(印加帝国).

The Inca Empire reached the height of its power in 15th- and l6th-century Peru (秘鲁). When the Spanish arrived, the Inca had established the largest and most complex society in the Americas, but they left behind no written records. The only ones the Inca are known to have kept are in the form of khipus. In 2002, Urton began Harvard s Khipu Database Project. He traveled to museums around the world to record the numbers of knots, lengths of cords, colors of fibers, and other details about every Inca: khipu he could find.

Urton says he and other researchers in the field have always had a general sense of what the khipus represented. Many had to do with census(人口普查) data. Others appeared to be calendar systems. But, until recently, none of the khipus Urton studied could be understood on a very detailed level.

A turning point came when Urton began looking into a set of six khipus from the 17th-centurySanta River Valley region of Northwest Peru. One day, Urton picked up a book and happened to spot a Spanish census document from the same region and time period. “A lot of the numbers that were recorded in that census record matched those six khipus exactly, Urton says. Then he couldn't help mentioning it to his students. Medrano, who was among these students, asked if he could help during spring break.

Urton agreed to allow Medrano to look into the Santa Valley khipus and the Spanish census. Medrano recalls looking through spreadsheets in Microsoft Excel. He noticed that the way each cord was tied onto the khipu seemed to correspond to(符合, 对应) the social status (地位) of the 132 people recorded in the census document. The colors of the strings also appeared to be related to the people's first names. After spring break, Medrano told his professor about his theories. Medrano worked with Urton over the next several months and the two wrote a paper together.