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Rafts and Rubber

In addition to excavating sites in Mexico, Hosler and her students are creating objects to test their theories about the construction techniques of ancient peoples, which ultimately provide insight into how they lived. Her work has inspired a wide range of student research projects, including efforts to built an Ecuadorian raft similar to those encountered by the Spanish during their conquest of northern South America and to discover how ancient Mexicans made rubber balls.

The raft project was an outgrowth of Hoslers previous studies on how metallurgy came to Mexico. After conducting detailed studies on hundreds of pre-Columbian Mexican metallic artifacts, she now believes that metalworking was brought to Mexico from two areas: one that included modern Ecuador, Peru, and Bolivia, and another that consisted of lower Central America and Colombia.

One theory is that Ecuadorians sailed north on rafts to exchange goods with early Mexicans. During her freshman seminar last spring, Hosler says, she told her students, Somebody tried to build one of these rafts, but it sank. Since youre MIT students, I bet your raft wouldnt sink. Within about three weeks, I had four or five volunteers.

Leslie Dewan 06, Ryan Bavetta 07, Danny Shen 05, and Daniel Cohen 06 managed to build a four-meter-by-four-meter raft in only a month on a budget of just $600. The students originally wanted to build the raft, which they dubbed PakpakaQuechua for little red owlout of balsa wood, but budget constraints forced them to compromise. Instead, they made logs out of chunks of Styrofoam covered in plywood. Its the same springiness, the same stability, and the same density as balsa wood, says Dewan, a nuclear-engineering major. The students used some 500 meters of rope to lash the Styrofoam logs together. Instead of the traditional cotton, they made the sail out of synthetic fabric left over from the creation of the Daedalus, an MIT-built, human-powered airplane that flew from Crete to Santorini in 1988.

In early August, Hosler and the students successfully launched and sailed the raft on the Charles River, cheered on by a crowd of students, faculty, and staff. The process of building and sailing the raft taught the students about some of the technical challenges the ancient sailors facedfor example, how to tie together the logs with rope, and how to use centerboards to steer the craft. Dewan, who has decided to minor in archaeology and materials, will continue the project this fall, using nautical-design software to simulate how six different types of ancient rafts move through the water. She intends to use the software to help determine which raft would be the best candidate for a sail from Ecuador to Mexicoan experiment Hosler hopes to conduct next summer.

Hoslers teaching spawned yet another research project. One day, in class, she described a ball game that had been popular throughout ancient Mesoamerica. Players volleyed a large rubber ball around a stone court and through a hoop. In some cases, the losing team was decapitated as part of a religious ritual. Michael Tarkanian 00, SM 03, asked Hosler how the balls were made. Professor Hosler said no one has ever worked on that, or even thought about it, he recalls.

That question drove Tarkanian to spend much of his time as an undergraduate and as a masters student piecing together a recipe. During his freshman year, he got firsthand information from Mexicans who had made rubber balls out of latex from rubber trees when they were children. After being mixed together with juice from a species of morning glory vine, the milky latex formed a solid rubber ball. As a graduate student, Tarkanian brought liters of latex and meters of morning glory vines to MIT, where he figured out how different combinations of the two would affect the mechanical properties of the rubber. For instance, some combinations resulted in tougher rubber, which may have been useful in making shoes, and others resulted in more bouncy rubber, which could have been better for the balls. Now, as a research affiliate in the archaeology and materials program, Tarkanian is using cutting-edge software to model the ball motion and figure out how the game may have been played. For instance, Tarkanian wants to determine where players would have to stand on the court in order to be physically able to volley a five-kilogram ball through a hoop.

Although it may seem unusual to devote seven years to studying a particular kind of rubber ball, Tarkanians experience is typical. We go to enormous lengths to get one little tiny bit of information, says Hosler. And in some cases, one little piece of information can totally repudiate theories that took decades to develop. Its very exciting, Hosler says. Its the way creative work should be, because we cannot take anything for granted. Its impossible to be too wedded to any particular theory, because the data speak, and they tell stories that are not necessarily the same things that archaeologists would like the data to tell us. Hosler is confident that, by approaching questions from the point of view of engineers, she and others in the MIT program will dig up a wealth of new information about ancient civilizations, one piece of data at a time.

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