From the familiar seashells and corals, to the microscopic plankton that live in ocean surface waters, the calcium carbonate skeletons produced by these organisms contain important clues to Earth history. By observing the microscopic growth of calcium carbonate crystals using the atomic force microscope, researchers have observed for the first time the fundamental physical processes that help govern climate change and ocean chemistry through the formation of biominerals.
The research by geological sciences Ph.D. student Kevin J. Davis and geochemist Patricia M. Dove, both at Virginia Tech, and crystal growth physicist James J. De Yoreo of Lawrence Livermore National Laboratory was published in Science on Nov. 10, 2000 ("The Role of Mg2+ as an Impurity in Calcite Growth").
The calcium carbonate biominerals that are produced by ocean creatures to fulfill biological needs eventually settle to the bottom of the ocean to form much of the sea-floor sediment. The process of crystallizing ions from the seawater to form the minerals in their shells removes carbon dioxide (CO2) from the atmosphere, which is a greenhouse gas thought to cause global warming.
Magnesium is the principal impurity in seawater that interferes with the growth of the calcium carbonate minerals so critical to the survival of many organisms. However, the actual mechanism by which magnesium alters calcium carbonate growth has remained controversial for the past 25 years. Davis and his colleagues resolved this long-standing controversy. "By comparing molecular-scale measurements with theoretical crystal growth impurity models we were finally able to achieve a physical understanding of the way in which magnesium modifies calcium carbonate growth," he explains.
Davis’ research grew from his interest in earth sciences. “I like to see how the basic processes that occur at mineral surfaces relate to the big picture of how the Earth system works.”
The research demonstrated that magnesium increases mineral solubility, which reduces calcite growth. "Magnesium inhibits growth by altering the equilibrium thermodynamics of the new growth surface by becoming part of the calcite lattice at the molecular level," Davis says. "The incorporation of magesium into calcite inhibits mineralization by causing strain in the crystal and increasing its solubility."
Many biominerals are so well adapted to their individual roles that they exhibit remarkable properties, making the processes involved in "biomineralization" of interest to a wide array of scientific disciplines. Another reason the biomineralization process is of interest is because organisms are able to create structures of astonishing complexity that are remarkably strong but lightweight. However, scientists are unable to produce materials with similar properties.
"This research brings us a step closer to understanding how organisms are able to form crystalline materials with unique structural properties," says Davis. "We hope to eventually develop new materials based upon the complex strategies used by organisms to produce their own mineral shelters. These materials will allow us to develop new lightweight ceramics for medical and high-tech applications."
The research was funded by the U.S. Department of Energy (DOE) Division of Chemical Sciences, Geosciences, and Biosciences.
Davis' research grew from his interest in earth sciences. "I like to see how the basic processes that occur at mineral surfaces relate to the big picture of how the Earth system works." The presence of magnesium in calcium carbonate biominerals is used by scientists as an indicator of past climates. “Ancient seawater temperatures can be determined from the amount of magnesium present in calcium carbonate biominerals,” Davis says. From there he became interested in the process. Now the funding for his research comes from both those interested in climate change (the National Science Foundation) and those interested in the development of new materials (DOE). He won the Gold Award for outstanding graduate research from the Materials Research Society for his molecular-level study of the biomineralization process.
Davis, who grew up in Richmond and is a graduate from Monacan High School in Richmond (1993), received his bachelor of science degree in biochemistry from the University of Virginia in 1997, his master's degree in geochemistry from Georgia Tech in spring 2000, and is now a Ph.D. student in geological sciences at Virginia Tech.
Learn more about Biochemistry of Earth Processes.
