INGERSON LECTURE: TOWARD A NEW PARADIGM FOR CALCIFICATION: DECIPHERING CARBONATES THROUGH THE LENS OF MULTIPLE PATHWAYS TO MINERAL FORMATION

The influence of environmental change on biological and inorganic calcification processes is at the center of many forefront questions in the earth sciences. Efforts to decipher paleoenvironmental signals from biogenic and sedimentary deposits are dependent upon accurately interpreting how physical and chemical conditions are recorded at the time of mineralization. Looking forward, the scientific community is calling for an understanding of how skeletons and tests of calcifying marine organisms will respond to the consequences of increasingly acidified oceans. Both lines of inquiry are now faced with the realization that long-standing 'principles' of calcification are undergoing a remarkable paradigm shift away from the idea that environmental effects must be interpreted within the concepts of classical crystal growth. Overwhelming evidence from structural biology shows that most carbonate-producing organisms form skeletons by nonclassical growth processes. That is, most biogenic calcification begins with the accumulation and storage of an amorphous phase that transforms to a composite of mesoscopically structured crystals (mesocrystals). This emergent idea calls for a critical course correction because: 1) hundreds of studies are founded on the assumption that skeleton formation is governed by principles of classical crystal growth and 2) early work is showing this new (but very old) nucleation-dominated process obeys a different set of dependencies upon chemical and environmental conditions from those established for classical growth. The presentation will highlight findings from recent efforts to uncover factors that influence mesocrystal formation and the controls of this pathway on the resulting Mg signatures.