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The Secret Life of Rocks
To children a rock is something to climb or throw; to an architect, it is a building material; to a geologist, rocks are ledgers upon which are written the history of our planet. Rocks, for most people, are inanimate fragments of the Earth that may be moved or shaped by outside forces — certainly not dynamos capable of shaping the world around them.
SETI Institute scientist Dr. Friedemann Freund, however, is not "most people." In his view, rocks are ancient factories where complex and important chemistry takes place. On early Earth, this chemistry may have provided molecules essential to the origin of life. It may also have helped contribute to the rise of an oxygenated atmosphere, and ultimately to the development of oxygen-tolerant, complex organisms like ourselves.
Early Years
Freund recalls his childhood in Germany on the eve of World War II, a time of "constant fear, of brushes with concentration camps and bombing raids." He recalls an early fascination with the beauty of the natural world that drew him towards biology. The young boy collected insects, "knew the names of all the butterflies," and gained some notoriety for his large collection of beetles.
"I read books about anything that I could put my hands on," he remembers. "In the beginning mostly history, then biology, later mostly physics." There was no doubt in the boy's mind he would become a scientist. During the war, Freund attended school for two years in Geneva, excelling in his studies despite his unfamiliarity with the French language. He returned to Germany for college, and received his undergraduate degree in chemistry, and then found himself "captivated by the beautiful colors of thin sections of crystals and rocks." Freund switched from chemistry to mineralogy-crystallography, and wrote his Ph.D. dissertation on highly disordered layer-type clay structures. His graduate work led to an enduring interest in crystal defects.
Interesting Imperfections
When most of us think of crystals we imagine lovely, regular geometric shapes with angular faces that are often shiny. It seems counter-intuitive that scientists should find structural imperfections the most attractive feature, but it is actually in the misalignments and structural flaws that "everything that is really interesting happens."
Freund explains, "I was mostly after defects that others had overlooked or thought to be unimportant. Early on I stumbled onto such a family of defects. This was an ignored field in both solid state physics and the geosciences, imperfections that arise when crystals grow in the presence of, and interact with, water, carbon dioxide and nitrogen."
Fundamental Discovery
While studying this "ignored field," Freund made a fundamental discovery that he believes will "probably have far reaching consequences." He found that minerals, that crystallize or recrystallize in the presence of common gases interact with them, that these gases enter into the crystal structure in very small concentrations, and that the oxygen anions (negatively charged ions) behave in unexpected ways. Oxygen anions, which normally carry two negative charges, could donate one of their electrons to hydrogen, carbon, and nitrogen derived from the dissolved gas—thus chemically reducing these elements. A second consequence of this odd behavior is that the oxygen anions in turn become oxidized from their normal "2-state" to the peroxy state.
"On one hand," Freund explains, "you end up having chemically reduced H, C, and N in minerals that slowly cool from high, magmatic temperatures. Under these conditions, a special form of 'organic chemistry' begins inside the dense, hard mineral matrix that looks so forbidding. It happens when carbon atoms are pushed around and assemble to form C-C-C chains and other sequences. Hydrogen atoms attach themselves to the carbon, and nitrogen joins in the game." Freund explains that complex proto-organic molecules appear inside the minerals, existing side by side with the peroxy bonds.
Rock Weathering and the Rise of Oxygen
During weathering, all the proto-organic molecules formed in the imperfections of the crystal structures are released into the environment. At the same time, the peroxy bonds turn into highly reactive hydrogen peroxide. During global weathering on the early Earth, hydrogen peroxide may have been released in sufficient quantities to "slowly but inextricably set our planet on the path toward an ever—increasing level of oxidation."
The constant release of hydrogen peroxide at the mineral-water interface may have profoundly influenced life's evolution, forcing primitive life forms that thrived in reduced environments to develop enzymatic defenses against the incessant peroxide assault. Freund and NASA microbiologist, Dr. Lynn Rothschild are investigating the possibility that microorganisms "may have become so good at fending off the potentially lethal oxygen that they could begin using its energy-rich potential." If Freund and Rothschild are correct, the transition to aerobic life may have had a "rocky beginning," but in the end gave rise to complex, oxygen-respiring organisms, including those who are capable of pondering their origins.
When asked what he would say to a young scientist just starting out, Freund recommends research as a deeply satisfying experience for the creative spirit. "Nothing is more exciting and rewarding," he says, "than to go on a lifelong quest to discover something that nobody else has ever seen before."
July 22, 2003