TIME’S ARROW IN THE TREES OF LIFE AND MINERALS

David Veblen was a polymathic advisor who encouraged his students to think beyond the atomic scale of transmission electron microscopy and to consider mineral microstructures within a larger geological and historical context. In this tribute to David’s lasting impact on mineralogy, I will discuss the degree to which mineralogists can borrow the botanical metaphor appropriated by Charles Darwin to illustrate biological speciation – the Tree of Life. Darwin’s allegorical Tree aligned precisely with the taxonomical system that Linnaeus developed a century earlier to classify living species, because an underlying mechanism – biological evolution – has driven the diversification of organisms over vast periods of time. In his zeal, however, Linnaeus (1758) extended his “universal” organizing system not only to the kingdoms of animals and plants but to stones as well -- his Regnum Lapideum. In doing so, Gould (2000) has argued, Linnaeus “clearly over-reached,” because “the logic that correctly followed the causes of order in the organic world … could not be extended to cover inorganic objects notbuilt and interrelated by ties of genealogical continuity and evolutionary transformation.”

Nevertheless, a consideration of the competition among proposed mineral taxonomies based either on external character (Werner), crystallography (Haüy), or chemistry (Berzelius) suggests that differences in the selection mechanisms that govern the evolution of organisms and of mineral species have obscured significant similarities in the systems by which we classify them. The ultimate and complete triumph of a chemistry-based Berzelian taxonomy, as embedded within the widely adopted system of James Dwight Dana, is consonant with a Linnaean classification paradigm, and it reflects Earth’s episodic but persistent progression with respect to chemical differentiation. In this context, Hazen et al.’s (2008) pioneering work in mineral evolution reveals that even the temporal character of the phylogenetic Tree of Life is embedded within a Danean framework for ordering minerals.