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Evolution of Minerals by Robert M GEOLOGY Evolution of Minerals BY RoberT M. HAZEN Looking at the mineral kingdom through the lens of deep time leads to a startling conclusion: most mineral species owe their existence to life nce upon a time there were no minerals ite, both pure forms of the abundant element anywhere in the cosmos. No solids of carbon, were likely the first minerals. They were Oany kind could have formed, much less soon joined by a dozen or so other hardy micro- survived, in the superheated maelstrom follow- crystals, including moissanite (silicon carbide), ing the big bang. It took half a million years be- osbornite (titanium nitride), and some oxides fore the first atoms—hydrogen, helium and a bit and silicates. For perhaps tens of millions of of lithium—emerged from the cauldron of cre- years, these earliest few species —“ur-minerals”— KEY CONCEPTS ation. Millions more years passed while gravity were the only crystals in the universe. ■ Only a dozen minerals (crystal- coaxed these primordial gases into the first neb- Earth today, in contrast, boasts more than line compounds) are known to ulas and then collapsed the nebulas into the first 4,400 known mineral species, with many more have existed among the ingre- hot, dense, incandescent stars. yet to be discovered. What caused that remark- dients that formed the solar Only then, when some giant stars exploded able diversification, from a mere dozen to thou- system 4.6 billion years ago, to become the first supernovas, were all the oth- sands of crystalline forms? Seven colleagues and but today Earth has more than er chemical elements synthesized and blasted I recently presented a new framework of “min- 4,400 mineral species. into space. Only then, in the expanding, cooling eral evolution” for answering that question. ■ Earth’s diverse mineralogy de- gaseous stellar envelopes, could the first solid Mineral evolution differs from the more tradi- veloped over the eons, as new pieces of minerals have formed. But even then, tional, centuries-old approach to mineralogy, mineral-generating processes most of the elements and their compounds were which treats minerals as valued objects with dis- came into play. too rare and dispersed, or too volatile, to exist as tinctive chemical and physical properties, but ■ Remarkably, more than half of anything but sporadic atoms and molecules curiously unrelated to time—the critical fourth the mineral species on Earth among the newly minted gas and dust. By not dimension of geology. Instead our approach uses owe their existence to life, forming crystals, with distinct chemical compo- Earth’s history as a frame for understanding which began transforming the sitions and atoms organized in an orderly array minerals and the processes that created them. planet’s geology more than of repeating units, such disordered material fails We quickly realized that the story of mineral INDEM two billion years ago. to qualify as minerals. evolution began with the emergence of rocky L —The Editors Microscopic crystals of diamond and graph- planets, because planets are the engines of min- HOLLY 58 SCIENTIFIC AMERICAN March 2010 © 2010 Scientific American www.ScientificAmerican.com SCIENTIFIC AMERICAN 59 © 2010 Scientific American [TIMELINE] Snapshots of Mineral Genesis n the 4.6 billion years since the Isolar system formed, the suite of minerals present has evolved from modest beginnings—about a dozen minerals in the presolar nebula— to better than 4,400 minerals found on Earth today. The planet has passed through a series of stages, represented at the right and in the following pages by five snapshots, involving a variety of mineral-forming processes. Some Making Earth of these processes generated 4.6 BilliON YEARS agO: Millions of planetesimals form in the disk of dust and gas that Zircon completely new minerals, whereas remains around the recently ignited sun (in background) and collide to form Earth others transformed the face of the (glowing planet). More than 200 minerals, including olivine and zircon, develop in the planetesimals, thanks to melting of their material, shocks from collisions, planet by turning former rarities and reactions with water. Many of these minerals are found in ancient chondritic meteorites. into the commonplace. Olivine crystals in pallasite (meteorite) Chondrite (meteorite) eral formation. We saw that over the past four vast rotating disk around the star. These left- and a half billion years Earth has passed through overs progressively clump into larger and a series of stages, with novel phenomena emerg- larger bits: sand-, pebble- and fist-size ing at each stage to dramatically alter and enrich fluff balls of primordial dust harboring [THE AUTHOR] the mineralogy of our planet’s surface. a limited repertoire of a dozen or so ur- Some details of this story are matters of in- minerals, along with other miscella- tense debate and will doubtless change with fu- neous atoms and molecules. ture discoveries, but the overall sweep of mineral Dramatic changes occur when ); evolution is well-established science. My col- the nascent star ignites and bathes the nearby leagues and I are not presenting controversial new concentrations of dust and gas with a refining pallasite data or radical new theories about what occurred fire. In our own solar system, stellar ignition oc- ONDON ( at each stage of Earth’s history. We are, rather, curred almost 4.6 billion years ago. Pulses of heat L recasting the larger story of that history in the coming from the infant sun melted and remixed USEUM, light of mineral evolution as a guiding concept. elements and produced crystals representing M I do, however, want to emphasize one intrigu- scores of new minerals. Among the crystalline Robert M. Hazen, senior staff ) scientist at the Carnegie Institu- ing insight: most of Earth’s thousands of miner- novelties of this earliest stage of mineral evolu- tion’s Geophysical Laboratory and ATURAL HISTORY chondrite als owe their existence to the development of life tion were the first iron-nickel alloys, sulfides, N ( ); Clarence Robinson Professor of on the planet. If you think of all the nonliving phosphides, and a host of oxides and silicates. Earth Science at George Mason world as a stage on which life plays out its evo- Many of these minerals are found in the most University, received his Ph.D. in illustrations earth science at Harvard University lutionary drama, think again. The actors reno- primitive meteorites as “chondrules”: chilled in 1975. He is author of 350 scien- vated their theater along the way. This observa- droplets of once molten rock. (These ancient Photo Researchers, Inc. tific articles and 20 books, includ- tion also has implications for the quest to find chondritic meteorites also provide the evidence ); RON MILLER ( ing Genesis: The Scientific Quest signs of life on other worlds. Sturdy minerals for the ur-minerals that predated chondrules. for Life’s Origin, and he frequently Hazen rather than fragile organic remains may provide Mineralogists find the ur-minerals in the form of presents science to nonscientists ASSIMOBREGA M through radio, television, public the most robust and lasting signs of biology. nanoscopic and microscopic grains in the ); lectures and video courses. Hazen’s meteorites.) zircon ( ING COMPANY ( recent research focuses on the role Making Earth In the ancient solar nebula, chondrules quick- ch EA of minerals in the origin of life. The T Planets form in stellar nebulas that have been ly clumped into planetesimals, some of which E mineral hazenite, which is precipi- H Getty Images seeded with matter from supernovas. Most of a grew to more than 100 miles in diameter—large A tated by microbes in the highly C alkaline Mono Lake in California, nebula’s mass rapidly falls inward, producing enough to partially melt and differentiate into IENTIFI COURTESY OF T is named after him. the central star, but remnant material forms a onionlike layers of distinctive minerals, includ- SC 60 SCIENTIFIC AMERICAN March 2010 © 2010 Scientific American Black Earth 4.4 BilliON YEARS agO: The surface of lifeless Hadean Earth is largely black basalt, a rock formed from molten magma and lava. The next two billion years see about 1,500 minerals produced. Repeated partial melting of rock concentrates scarce, dispersed elements such as lithium (found in lepidolite), beryllium (in beryl) and boron (in tourmaline). Chemical reactions and weathering by the early oceans and the anoxic atmosphere also contribute. Minerals formed Lepidolite under high pressure, such as jadeite, are brought to the surface by plate tectonics. Beryl ing a dense, metal-rich core. Frequent collisions Tourmaline mantle (the nearly 2,000-mile-thick layer that in the crowded solar suburbs introduced intense extends from Earth’s iron-nickel core to the shocks and additional heat, further altering the three- to 30-mile-thick crust at Earth’s surface). minerals in the largest planetesimals. Water also Following this moon-spawning collision played a role; it had been around from the begin- about 4.5 billion years ago, the molten Earth be- ) ning, as ice particles in the presolar nebula, and gan the cooling that continues to this day. Al- in the planetesimals these melted and aggregated though Earth’s primitive surface included doz- tourmaline in cracks and fissures. Chemical reactions with ens of rare elements —uranium, beryllium, gold, ( the resulting water generated new minerals. arsenic, lead and many more—that were capable Perhaps 250 different mineral species arose of forming a diverse assortment of minerals, as a consequence of these dynamic planet-form- Theia’s impact had served as a cosmic “reset.” It ing processes. Those 250 minerals are the raw left Earth’s outer layers thoroughly mixed, with Photo Researchers, Inc. materials from which every rocky planet must these less common elements far too dispersed to ANA C form, and all of them are still found today in the form separate crystals.
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