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The fundamental properties of the neutron make it a powerful tool for Earth science investigations because neutrons provide information that cannot be obtained by any other research method. This is because neutrons are magnetically sensitive, nondestructive, and sensitive to the lighter elements, such as hydrogen. They provide a unique, nondestructive method for obtaining information ranging from Ångstrom-scale atomic structures (and related motions) to micron-scale material strain, stress, and texture, and even up to meso-scale porous matrices and defects in materials and functional components. In this article, we introduce neutrons and their unique properties, neutron production and sources, and provide an overview of the different types of neutron methods applicable to the Earth sciences.

Neutron scattering is a powerful tool to elucidate the structure and dynamics of systems that are important to geochemists, including ion association in complex aqueous solutions, solvent-exchange reactions at mineral–water interfaces, and reaction and transport of fluids in nanoporous materials. This article focusses on three techniques: neutron diffraction, which can reveal the atomic-level structure of aqueous solutions and solids; quasi-elastic neutron scattering, which measures the diffusional dynamics at mineral–water interfaces; and small-angle neutron scattering, which can show how properties of nanoporous systems change during gas, liquid, and solute imbibition and reaction. The usefulness and applicability of the experimental results are extended by rigorous comparison to computational simulations.

The global energy landscape has changed significantly in the last few years as a result of technological advances in the recovery of unconventional hydrocarbon resources such as tight oil and shale gas. Studies have been initiated to assess the impacts of extraction and production of unconventional hydrocarbons on surface water, groundwater, and local air quality. There is additional concern over how their extraction and utilization on a global scale may contribute to atmospheric chemistry and global climate change. This article provides an overview of opportunities and challenges offered by the abundance of unconventional hydrocarbons, the driving forces that encourage our rush to employ them, and the need for Earth scientists to engage in studies of their properties and impacts on the environment. A fundamental understanding of geological, mineralogical, and geochemical processes is integral to how we responsibly extract and utilize these resources.

Carbon dioxide capture and sequestration (CCS) in deep geological formations has recently emerged as an important option for reducing greenhouse emissions. If CCS is implemented on the scale needed to make noticeable reductions in atmospheric CO2, a billion metric tons or more must be sequestered annually—a 250 fold increase over the amount sequestered today. Securing such a large volume will require a solid scientific foundation defining the coupled hydrologic-geochemical-geomechanical processes that govern the long-term fate of CO2 in the subsurface. Also needed are methods to characterize and select sequestration sites, subsurface engineering to optimize performance and cost, approaches to ensure safe operation, monitoring technology, remediation methods, regulatory overview, and an institutional approach for managing long-term liability.

Human and industrial development over the past hundred years has led to a huge increase in fossil fuel consumption and CO 2 emissions, causing a dramatic increase in atmospheric CO 2 concentration. This increased CO 2 is believed to be responsible for a significant rise in global temperature over the past several decades. Global-scale climate modeling suggests that the temperature increase will continue, at least over the next few hundred years, leading to glacial melting and rising sea levels. Increased atmospheric CO 2 also leads to ocean acidification, which will have drastic consequences for marine ecosystems. In an attempt to solve these problems, many have proposed the large-scale sequestration of CO 2 from our atmosphere. This introductory article presents a summary of some of the evidence linking increasing atmospheric CO 2 concentration to global warming and ocean acidification and our efforts to stem this rise though CO 2 sequestration.