Ursula B. Marvin, Harvard lecturer on geology, has traveled to some pretty cold places to perform her research on meteorites.

Meteorites consist of pieces of cosmic matter which reach the Earth's surface. If the matter does not reach the surface, it is called a meteor. Meteors are the "shooting stars" seen in the night sky which result from the vaporization of bits of cosmic matter.

While scientists estimate that approximately one half-ton of meteorites falls to Earth every year, most of this matter is not recoverable. Meteorites can be found with relative ease, however, on the snow and ice of Antarctica, leading geologists like Marvin to travel there in search of samples.

Antarctica is uniquely suited for geological collection because upward ice motion combines with wind abrasion to bring meteorites to the surface in concentrated numbers. Over 13,000 samples have been gathered there by scientists from various nations.

Collecting meteorite samples is difficult for many reasons, Marvin says. Each day, geologists estimate, only four or five meteors are large enough to survive the trip through Earth's atmosphere without burning up completely. The majority of these fall into the ocean.

And finding the few meteorites that hit dry land is tricky because they frequently look just like terrestrial rocks.

"It's rare to collect a fallen meteorite," says Marvin. "They are precious samples."

Moreover, approximately 94 percent of meteorites are rocky, with the remainder being of the nickel-iron variety. The distinctive metallic appearance of nickel-iron meteorites makes them easier to spot, says Marvin.

Once Marvin has collected her samples, she slices them into thin wafers just 30 microns thick to test their optical properties and to perform chemical analyses.

Past geological research has uncovered evidence that meteorites, because of their chemical composition and age, may have played an important role in the formation of life on this planet.

According to Marvin, many of the samples pre-date the Earth's crust and may hold clues to the origins of the universe. Some meteorites have been estimated to be 4.5 billion years old, making them half a billion years older than the estimated age of the Earth's crust.

"These samples are less processed and more primitive," Marvin says. "They were not weathered in space."

Harvard Professor of Geology Raymond Siever adds that these ancient reminders from the past have been invaluable to scientists. "This is the only line of evidence to what has happened in the universe," he said.

A few meteorites have also contained traces of organic materials. "Some carry hydrocarbons, amino acids and fatty acids which are present in all living things," says Marvin.

Some researchers theorize that such content may have enabled meteorites to have been partially responsible for helping life develop on Earth.