Geologist Searches for Meteorites, Hopes for Clues to Earth's History

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.

"It's possible they contributed to the building blocks of life," the geologist says.

Meteors come from various locations in the universe, says Marvin. "They come from other planets, [from] rubble from asteroids, and a few from comets," she says.

A few lunar rocks have been found on Earth as well. Although the moon is physically close to the earth and is approximately the same age, its rocks do not resemble terrestrial rocks, says Marvin.

Since there is no water on the moon's surface and the atmosphere is nonexistent, Marvin says, lunar rocks change very little over time.

"We can look at a rock that formed four billion years ago and it looks like it formed yesterday," she said.

Terrestrial rocks, on the other hand, are highly susceptible to change from the elements, says Siever. "Most things are obliterated by erosion and weathering," he says.

A lot of information about the past can be gained by examining meteorites, Marvin says. Since cosmic rays continually bombard meteors in space, researchers can determine the age of meteors by using radioactive isotope dating techniques. This dating method allows scientists to infer what conditions prevailed when the sun and earth were formed, Marvin says.

Though extensive research is being done on meteorites, practical application of this information is still far away, say the geologist. Mining for minerals on other planets or asteroids is unlikely due to economic reasons.

"If you want to use a mineral, there has to be enough of it to mine profitably," Marvin said. "There are cheaper ways of getting minerals right now."