Evolution of Minerals

marc h 2010 H o ll y li n d em Once upon a time there were no minerals anywhere in the cosmos. No solids of any kind could have formed, much less survived, in the superheated maelstrom following the big bang. It took half a million years before the first atoms—hydrogen, helium and a bit of lithium—emerged from the cauldron of creation. Millions more years passed while gravity coaxed these primordial gases into the first nebulas and then collapsed the nebulas into the first hot, dense, incandescent stars. Only then, when some giant stars exploded to become the first supernovas, were all the other chemical elements synthesized and blasted into space. Only then, in the expanding, cooling gaseous stellar envelopes, could the first solid pieces of minerals have formed. But even then, most of the elements and their compounds were too rare and dispersed, or too volatile, to exist as anything but sporadic atoms and molecules among the newly minted gas and dust. By not forming crystals, with distinct chemical compositions and atoms organized in an orderly array of repeating units, such disordered material fails to qualify as minerals. Microscopic crystals of diamond and graphite, both pure forms of the abundant element carbon, were likely the first minerals. They were soon joined by a dozen or so other hardy microcrystals, including moissanite (silicon carbide), osbornite (titanium nitride), and some oxides and silicates. For perhaps tens of millions of years, these earliest few species—“ur-minerals”— were the only crystals in the universe. Earth today, in contrast, boasts more than 4,400 known mineral species, with many more yet to be discovered. What caused that remarkable diversification, from a mere dozen to thousands of crystalline forms? Seven colleagues and I recently presented a new framework of “mineral evolution” for answering that question. Mineral evolution differs from the more traditional, centuries-old approach to mineralogy, which treats minerals as valued objects with distinctive chemical and physical properties, but curiously unrelated to time—the critical fourth dimension of geology. Instead our approach uses Earth’s history as a frame for understanding minerals and the processes that created them. We quickly realized that the story of mineral evolution began with the emergence of rocky planets, because planets are the engines of minKey conceptS