The Society’s Distinguished Lecturers for 2023–24 have been selected. They are Clare Nicholls (University of Oxford) and Chris Greenwell (Durham University).
This year we will also have online presentations of lectures (details to be made available via the E-Bulletin).
Here are the venues (with dates in some cases) for Dr Nicholls and Prof. Greenwell:
Claire Nicholls
- University of Manchester (30th October 2023; Lecture B)
- University of Edinburgh/Glasgow (7/8th March 2024, Lecture A)
- University of Exeter (20th March 2024, Lecture A)
- University of Aberdeen (Lecture A)
Lecture A: What has Earth’s magnetic field ever done for us? The role of the geodynamo in creating a habitable planet
When considering why Earth is the only known habitable – and inhabited – world in our solar system, its magnetic field is often included as one of the many factors resulting in such favourable conditions for life. This is because magnetic fields protect planetary surfaces from harmful cosmic radiation and prevent the atmosphere from being eroded by the solar wind. Earth’s magnetic field is generated by the geodynamo; vigorous convection of electrically conductive molten metal in the outer core results in the dipolar magnetic field that surrounds our planet. We can use the signals preserved by magnetic minerals in rocks to examine the strength of Earth’s magnetic field back through geological time. However, this becomes increasingly challenging as metasomatic and metamorphic events cause these minerals to be altered or entirely replaced. Paleomagnetic records suggest that Earth’s magnetic field has been similar in strength for the last 3.5 billion years. However, there are many time periods with sparse data, and the existing data come with many caveats. New experimental approaches are now allowing paleomagnetists to revisit Earth’s early magnetic field history in a new light by combining magnetic microscopy, geochronology and petrology. By recovering more accurate records of Earth’s magnetic field strength through time questions such as how the geodynamo behaved prior to the nucleation of the inner core, and the role of Earth’s magnetic field in mediating atmospheric escape, can be addressed properly for the first time. These observations will be critical for determining whether the magnetic field really played a crucial role in creating habitable conditions on Earth’s surface.
Lecture B: Metals, Magnetism and Meteorites: A brief guide to magnetic field generation on small planetary bodies
Planetary magnetic fields are generated by vigorous convection of an electrically-conductive, molten metallic core. Paleomagnetic measurements have revealed that a surprising number of small planetesimals, with radii of just a few hundred kilometers, were able to sustain active magnetic fields in their early histories. This provides invaluable insight into their interior structure, formation and thermal histories. In order to extract these magnetic field histories, many novel experimental approaches have been utilized including synchrotron X-ray microscopy and quantum diamond microscopy. In particular, these methods have allowed paleomagnetic records to be extracted from tetrataenite, a mineral with an exceptionally robust ability to preserve records of magnetic fields that were active billions of years ago. Paleomagnetic records extracted from nanoscale tetrataenite structures in pallasite meteorites have demonstrated that the parent body must have had a large core and a thin mantle. Also, contrary to popular belief, these results show that pallasites do not represent core-mantle-boundary material. The formation of pallasite meteorites remains debated with several formation mechanisms currently in contention including ferrovolcanism, impacts and partial differentiation. By combining paleomagnetic data with petrological and geochemical observations, each of the proposed mechanisms can be systematically ruled in or out. Determining the nature and formation of small planetary bodies is key in understanding the processes that eventually resulted in the formation of the planets in our solar system today.
Chris Greenwell
- Cardiff University
- University College Dublin (6th March 2024, Lecture D)
- University of Greenwich (Lecture D)
Lecture C: Layered minerals and the origin of life on Earth
Given their likely ubiquitous nature, layered minerals such as the aluminosilicate clay minerals have featured prominently in discussions around the origin of life on Earth. One of the main challenges to address in origins of life theory is how the more complex molecules needed by the first biochemistry could have been assembled. Dilute precursor molecules needed to be concentrated from the early ocean to levels that reactions could occur, reactions promoted, and the resultant products protected from thermal or high energy ultraviolet degradation to enable further assembly. Characteristics such as high surface area, ion exchange capacity, a protective space between the sheets and intrinsic catalytic reactivity of layered minerals underpin their potential role in addressing the assembly of or proto-biomolecules. Over time, other layered minerals, in particular layered double hydroxide (LDH) minerals, have increasingly come to feature in hypotheses for the prebiotic chemistry that ultimately lead to the origin or life. LDH minerals are anion exchangers, with very high concentration power, and have been shown to uptake a range of potentially interesting precursors to biomolecules. As understanding of the properties of layered minerals has improved over the years, the potential for reduction-oxidation chemistry, layer flexibility, regioselective catalysis and dynamics and templating effects have added to the interest in these minerals in prebiotic chemistry studies. This lecture will introduce the range of prebiotic chemistry studies involving layered minerals and demonstrate how both computational and experimental studies have added insight not the structure, dynamics and reactivity of layered minerals through the lens of prebiotic chemistry.
Lecture D: Swelling, wettability alteration and applications of clay and other layered minerals
Those with clay rich soils in their gardens will be all too familiar with the macroscopic manifestation of clay hydration, with shrinkage cracks in the dry spells of summer and loss of cohesion during rainy spells. Layered minerals, such as clay minerals, are comprised of 2-dimenaional layers, in which all the atoms are bonded to one another reasonably strongly, with each layer then stacking with weaker interactions between, one above the other, to give the clay crystal. Many layered minerals have isomorphous substitution resulting in layers that carry a permanent charge. These permanent charges are counter balanced by ions of the opposite charge, sitting in the interlayer space, which have differing enthalpy of hydration according to the type of ion, and the specific site it sits at on the clay mineral surface. The relative affinity for a mineral surface for one fluid versus another it known as its wettability. Wettability and swelling in different solvents or brines is critically important for many industrial applications of clay minerals, or for addressing problems caused by the swelling of clay minerals, for example in fluid migration and/or wellbore stability. This talk will discuss the swelling and instability of clay and other clay-like layered minerals in different solvents and its implications for applications of, and problems caused by, clay and layered minerals in a variety of settings of industrial relevance.