“Mineral evolution,” the study of Earth’s changing near-surface mineralogy, frames Earth materials research with a historical narrative. This 4.5-billion-year story integrates themes of planetary science, including geodynamics, petrology, geochemistry, thermodynamics, geobiology, and more. Mineralogy thus holds the key to unlocking our planet’s history and assumes its rightful central role in the Earth sciences. The mineralogy of terrestrial planets evolves as a consequence of physical, chemical, and biological processes. Starting with ~12 refractory minerals in prestellar molecular clouds, processes in the solar nebula led to the ~250 different minerals found in meteorites. Initial mineral evolution of Earth’s crust depended on a sequence of geochemical and petrologic processes that resulted in an estimated 1500 different mineral species. Ultimately, biological processes produced large-scale changes in atmospheric and ocean chemistry that may be responsible, directly or indirectly, for most of Earth’s 4400 known mineral species. Mineral evolution thus highlights the coevolution of the geo- and biospheres.
This issue of Elements focuses on the geochemistry of sulfur in high-temperature, low- temperature, and biogenically mediated processes over a wide range of scales, environments, and time intervals. Sulfur’s multiple valence states (S2- to S6+) allow for its participation in a large variety of geochemical and biogeochemical processes. Sulfur may be one of the light elements contained in the Earth’s core and may have been crucial in core formation. Sulfur is an essential component in all life on Earth. Sulfur geochemistry continues to be used in delineating the early evolution of Earth’s atmosphere and hydrosphere, as a monitor of volcanic SO2 and H2S, and as a tracer of anthropogenic sources. Recent advances in the use of multiple sulfur isotopes (32S, 33S, 34S, and 36S) and in situ isotopic measurements will allow sulfur stable isotopes to develop as vital tracers in the Earth and planetary sciences, with applications to inorganic and biogenic processes.
Fluids play a critical role during metamorphic processes. They have first-order influence on both reaction kinetics and mass transfer, and thus also on the rate of metamorphism. “Volatile components,” such as H2O and CO2, may strongly influence rock rheology even in the absence of a free fluid phase. Metamorphic fluids therefore control the coupling between chemical reactions, mass transport, and deformation. Microstructures, compositional gradients at various scales, and larger-scale deformation features all reflect the dynamics of fluid–rock interactions. Moreover, the migration of fluids produced during prograde metamorphic processes or consumed during retrogression links metamorphism with the hydrosphere, the atmosphere, and the biosphere. This issue sheds light on the origin of the various patterns that emerge in metamorphic rocks as a response to changes in pressure, temperature, and the composition of pore-filling fluid. By following the metamorphic fluids to or from the Earth’s surface, we also aim to explain how metamorphism may affect our own environment.
Solid atmospheric particles range in size from a few nanometers to several micrometers and are generated through both natural processes and human activity. Even though these particles are derived from spatially limited source areas and typically become airborne during short-term events, they are ubiquitous globally due to atmospheric circulation. Depending on their physical and chemical properties, these solid aerosols have a major impact on the radiative properties of the atmosphere and glaciers, on cloud condensation, and on the chemical composition of oceans and soils. Because these particles affect transportation and human health, they have recently become the focus of government attention and regulation.
This issue of Elements explores the atmosphere as an exciting new research area for mineralogists and geochemists. It illustrates the most prominent types of atmospheric particles and discuss their key effects on climate and ecosystems worldwide.
During the past decades, thermodynamics has become an essential tool for understanding fundamental processes that have determined the structure and evolution of our planet. From the atmosphere to the ocean and sediments, from metamorphic terranes to magmatic provinces, the lower mantle, and the core, this issue of Elements will illustrate how a better understanding of the manner in which free energy depends on temperature, pressure, and chemical composition allows the Earth’s activity to be better deciphered. At a time when climate change has become a major concern, thermodynamic studies of the atmosphere and ocean have not only an academic interest, but also considerable practical importance.
Humanity requires healthy soil in order to flourish. Soil is central to food production, regulation of greenhouse gases, and provision of amenity. But soil is fragile and easily damaged by uninformed management or accidents. One source of damage is contamination with the chemicals that are used to provide the lifestyles to which the developed world has become accustomed. Repairing or cleaning up this damage so that soil can again be used for beneficial purposes is a vitally important task. Traditionally, soil “clean up” involved removing the contaminated soil and replacing it with clean soil from elsewhere. Clearly this is not sustainable. Increasingly researchers and practitioners look to clean up contaminated soil and make it good for reuse rather than simply discarding it. Mineralogy and geochemistry are central to the design and implementation of many of these new approaches.