BIOMINERALIZATION: NANOSCALE APPROACHES TO DECIPHERING THE ORIGINS OF THE VITAL EFFECT

The processes by which organisms mediate the formation of minerals and amorphous materials are broadly known as biological mineralization. Because the interactions between organisms and their abiotic environments are central to understanding past and future earth environments, biomineralization processes have become an urgent research topic in geobiology.

Scientists have long noted that the compositions of some biominerals reflect well the conditions under which the organisms lived while others give poor representations. This is problematic because reliable interpretations of compositional proxies require accurate sorting of true environmental signals from effects imposed by biological activity, the so-called ‘vital effect’. To date, the solution has been to use taxa that appear to be good proxies while avoiding others. This approach, however, perpetuates concerns that in the absence of a deep understanding of vital effects, it is almost impossible to know when the recording is really faithful. This is particularly acute in discerning equilibrium versus non-equilibrium effects.

With recent advances in experimental and computational methods, the mineralogical and biological sciences are poised to develop a mechanistic understanding of biomineralization processes. In situ microscopies and spectroscopies are revealing underlying principles of mineral assembly that may give insights to chemical and biological controls on the “synthesis” of biogenic materials and their compositional signatures. This mechanistic approach is essential to deciphering how basic mineralization processes lead to compositional variations observed in natural samples.

In one example of this kind of approach, we are investigating the nanoscale interactions of two proxy elements, Mg and Sr, on calcite mineralization. By discerning the kinetic and thermodynamic effects of these impurities on growth dynamics at the scale of monomolecular steps, we are also gaining insights to controls on macroscopic crystal morphology. The observed mechanisms of growth modification and the accompanying signatures are highly diverse, but in all cases, we are finding that step-specific interactions provide the underlying mechanism of growth modification.