Proposals for Summer internships 2024
Lead supervisor: Catriona McDonald, Institute of Astronomy
Co-supervisors: Richard Anslow, Institute of Astronomy; Amy Bonsor, Institute of Astronomy; Paul Rimmer, Cavendish Laboratory
Research proposal
A scenario which has long been implicated in the origins of life on Earth is the delivery of prebiotic feedstock molecules via cometary impacts (Oró 1961). Previous work suggests that significant quantities of prebiotic molecules are only able to survive the violent impact process inside small comets with low impact velocities (Pierazzo & Chyba 1999). During the late stages of planet formation, the terrestrial planets experienced a prolonged period of impacts by comets, scattered into the inner Solar System by the giant planets.
Uncertainties remain regarding the detailed dynamical history of the solar system which drives cometary impacts. Thus, there remains questions about how the inventory of prebiotic molecules delivered by cometary impacts differs amongst the terrestrial planets.
The student will work with Richard Anslow and Catriona McDonald to produce a simulated chronology of cometary impacts onto the terrestrial planets using a Monte Carlo-type approach. The student will consider multiple models of the solar system’s dynamical history to determine when cometary delivery may have been possible for the early-Earth which will constrain the global environmental conditions relevant for the emergence and development of life (e.g., Nesvorny et al. 2023). This will involve combining observed comet size-frequency distributions with an impact velocity distribution which the student can determine either numerically or analytically depending on their interests (e.g., Nesvorny et al. 2017, Anslow et al. 2023).
Using previous studies in the literature (e.g., Todd & Öberg 2020), and ongoing research from Richard Anslow and Catriona McDonald on the physical processes related with cometary impacts, the student will determine a set of criteria required for an impact to successfully deliver prebiotic molecules. The criteria will involve the comet’s size, composition and impact velocity and angle. The overall inventory of prebiotic molecules successfully delivered to the early-Earth under different solar system histories can then be determined, informing the relative feasibility of cometary delivery. Further, this project will investigate how this conclusion will change for the other terrestrial planets in the solar system, Mars and Venus, which have different bulk, and orbital parameters to the Earth.
Relevant expertise
Richard Anslow, Catriona McDonald and Amy Bonsor all have expertise in the dynamics of small bodies in planetary systems. Catriona McDonald has expertise in the physics of cometary impacts, using 3D simulations of oblique cometary impacts, and modelling the survival of prebiotic molecules. Richard Anslow has expertise in simulating the dynamics of comet impacts, and is currently using the lunar crater record to constrain cometary impact scenarios on the early-Earth. Paul Rimmer has expertise in the chemical networks relevant for the survival of prebiotic molecules.
References
- Oró 1961, Nature
- Pierazzo & Chyba 1999, Meteoritics & Planetary Science
- Nesvorny et al. 2023, Icarus
- Nesvorny et al. 2017, The Astrophysical Journal
- Anslow, Bonsor & Rimmer 2023, Proc. R. Soc. A
- Todd & Öberg 2020, Astrobiology
Lead supervisor: David Buscher, Department of Physics
Research proposal
The detection of "Earth twins'' – rocky planets orbiting at radii of order 1au around solar-type stars – will be one of the major stepping-stones in our search for life in the Universe. One of the most promising avenues to make these detections is to use extreme-precision radial-velocity (EPRV) spectrographs to detect the minute (10 cm/s) stellar reflex Doppler signals caused by the Earth twin.
A critical element to obtaining this 10cm/s precision is calibrating the wavelengths of the spectral features used for radial-velocity measurement to better than 1/10,000th of a spectrograph pixel. This project aims to test a new strategy for this extreme precision calibration, involving projection of interferometric fringes on the spectrograph pixels and Bayesian analysis of these fringe patterns to derive an extremely accurate map of pixel-by-pixel wavelength variations in the spectrograph.
The project will involved developing software in Python to implement this Bayesian data-analysis strategy and testing it on simulated fringe data which includes simulated disturbances such as vibrations and temperature fluctuations. The end product will be a prediction of the achievable performance of such a system under realistic conditions.
The lead applicant is an expert in the analysis of interferometric data and is involved in calibration of the ANDES high-resolution spectrograph.
Supervisor: Emily Mitchell, Department of Zoology
Co-supervisor: Euan Furness, Department of Zoology
Research proposal
The number of species of animal on Earth has changed extensively over the Phanerozoic (the last 539 million years). However, the mechanisms controlling this change are still debated, with a key hypothesis being that macroevolutionary patterns tend towards equilibria (a phenomenon called “density dependent diversification”), with perturbations from these equilibria (e.g. mass extinctions) being counteracted by changes in rates of speciation and/or extinction in the aftermath (Benson et al. 2016). However, an alternative hypothesis posits that these equilibria do not exist, or at the very least that they are not impactful, and that global species richness shows a pattern of gradual exponential growth (“density independent diversification”), dampened by extinction events (Benton & Emerson 2007, Cermeño et al. 2022). Density-dependence has usually been proposed to arise as a product of a negative relationship between population size and extinction risk (MacArthur & Wilson 1963). However, ecosystem engineering (the modification of the environment by organisms) also presents a plausible source of density dependence, as the extinction of ecosystem engineers could result in losses of other species that were dependent upon the engineered environment (Erwin 2008).
Neither density-dependent nor density-independent diversification relies upon specific biological properties of the species that it models, and both make relatively few base assumptions. Consequently, these mechanisms are highly amenable to analysis using computer simulation systems. However, with relatively few exceptions (Alroy 2008), simulation studies have tended to simulate models at one extreme or the other of density dependence when, in reality, a variety of intermediate models, combining aspects of the two extremes, are plausible and, arguably, more likely.
The LCLU internship student will construct a simulation model of biodiversity in the coding language of their choice, in the vein of the model of Alroy (2008). This model will include a number of parameters describing the degree and mechanisms of density dependence within the model, including the impact of density on abiotic factors (i.e. ecosystem engineering effects) and their feedbacks on diversity. The student will investigate how varying these parameters leads to variations in simulated biodiversity, speciation and extinction rates, and how these impact the abiotic environment. These variations will be compared with data drawn from the empirical fossil and geological record.
The host team is experienced with programming in C++ and Python, and with using these programs to both handle data and model a range of biological phenomena, including change in diversity over geological time. Both hosts are members of the Department of Zoology, and are familiar with the biological underpinnings of the questions to be studied.
The applicant must have a strong understanding of and interest in programming in at least one coding language, ideally python (although other languages are viable). The hosts will guide the student through any unfamiliar biological concepts; no previous biology experience is required.
Citations
- Alroy (2008) - Dynamics of origination and extinction in the marine fossil record. (See SI for model).
- Benson et al. (2016) - Near-stasis in the long-term diversification of Mesozoic tetrapods.
- Benton & Emerson (2007) - How did life become so diverse? The dynamics of diversification according to the fossil record and molecular phylogenetics.
- Cermeño et al. (2022) - Post-extinction recovery of the Phanerozoic oceans and biodiversity hotspots.
- Erwin (2008) - Macroevolution of ecosystem engineering, niche construction and diversity.
- MacArthur & Wilson (1963) – An equilibrium theory of insular zoogeography.
Lead supervisor: Paul B Rimmer, Cavendish Laboratory
Co-supervisor: Sai Murali, Cavendish Laboratory; Catriona McDonald, Institute of Astronomy; Amy Bonsor, Institute of Astronomy
Research proposal
Context: Cometary delivery has been proposed as a source of molecules that can facilitate life’s origins (Chyba et al. 1990). Recent calculations have suggested very little cometary material would survive delivery to Earth (Todd & Öberg 2020) or other planets (Anslow et al. 2023). However, experiments find that some prebiotic molecules, like glycolaldehyde, could survive impacts (Zellner et al. 2020). These experiments have not been run under conditions appropriate to comets. Specifically, they were run without water. Performing experiments for a larger set of molecules, with and without water, will be needed to provide empirical insight into what prebiotic chemistry is likely to be delivered by cometary impacts.
Objectives: Working with Murali & Rimmer, the student will experimentally determine the thermal stability of three compounds important for prebiotic chemistry: ferrocyanide, glycine and glycolaldehyde. Then, working with McDonald, Bonsor & Rimmer, the student will apply their experimental results to a computational model of a cometary impact.
Methodology: The student will investigate thermal stability of three different samples: ferrocyanide, glycine and glycolaldehyde, with and without water. For each sample, the student will place the sample in a sealed Argon-filled container with an empty balloon attached to the top to allow for gas expansion. In one case, the sample will be placed in dry, in the other with Argon-degassed water. The samples will be held at different temperatures for varying amounts of time. The sample will be cooled and analyzed using NMR and UV-Vis spectra to determine the surviving concentrations. In this way, the student will determine the temperature-dependent lifetimes of these molecules, with and without water. Cometary impact models that predict the comet’s impact temperature as a function of time can incorporate these timescales to predict how much of the molecule initially in the comet is expected to survive and be delivered to the surface of a planet.
Expected Outcome: Measurement of the lifetimes, activation energies and surviving concentrations of delivered material, applicable for a wide range of planetary conditions. The predicted lifetime of dry ferrocyanide at low temperature could provide insights into what traces of prebiotic chemistry are expected to have survived on the surface of Mars.
Relevant Expertise: Dr. Rimmer is expert in chemical kinetics experiments and models, and in origins research. Dr. Bonsor is expert in the dynamics of solar systems and the physics and chemistry of interplanetary material. Dr. Murali is expert in physical organic chemistry. Dr. McDonald is expert in computational models of cometary impacts.
References
- Anslow, Bonsor & Rimmer 2023. Can comets deliver prebiotic molecules to rocky exoplanets?. Proceedings of the Royal Society A, 479(2279), 20230434.
- Chyba et al. 1990. Cometary delivery of organic molecules to the early Earth. Science, 249(4967), 366-373.
- Todd & Öberg 2020. Cometary delivery of hydrogen cyanide to the early Earth. Astrobiology, 20(9), 1109-1120.
- Zellner, McCaffrey, & Butler 2020. Cometary glycolaldehyde as a source of pre-RNA molecules. Astrobiology, 20(11), 1377-1388.
Lead supervisor: Sasha Turchyn, Department of Earth Sciences
Co-supervisor: Bizhou Zhu, Department of Earth Sciences
Research proposal
Life didn't leave a great record of itself early in Earth history. At best we can hope for changes in the chemistry and mineralogy of rocks that we think are indicative of microbial activity. We are currently working in a model ecosystem which we think has similar mineralogy and microbial communities to rocks we find in the geological record. In the North Norfolk salt marshes the sediment is iron-rich and dominated by microbial communities that are reducing the iron while oxidising organic matter. Often there are areas of the salt marsh where the sediment has accumulated an excess of organic matter and the pond has become sulfidic, full of hydrogen sulfide and dominated by microbial sulfate reduction. The pond sediment that has sulfide also has methane.
We have been interested in the changes that happen to sediment when the iron rich mineralogy is exposed to sulfide through a change in microbial community assemblage. We have managed to do this before using a supply of carbon. This process mimics what happens in the real world when iron rich sediments are exposed to sulfide produced through microbial sulfate reduction during burial. This overprinting was likely common and we would like to figure out how we can recognised this microbial overprinting in the geological record.
The student will sample sediment from Norfolk and set up a series of incubations, feeding them different amounts of organic carbon. The student will monitor changes in the fluid chemistry as the cultures grow and then will sample the sediment and analyse the mineralogy and geochemistry of the sediment over time. This will be done using XRD, chemical speciation and Fourier Transform Infrared Spectrometry (FTIR). The equipment is available either in Earth Sciences or the Turchyn lab.
This project is linked to the other project in Norfolk and the students can work in parallel.
Professor Alexandra (Sasha) Turchyn is an environmental and isotope geochemist who studies sediment biogeochemistry. Bizhou Zhu is a PhD student in her group who will help supervise the day to day.
Lead supervisor: Sasha Turchyn, Department of Earth Sciences
Co-supervisor: Bizhou Zhu, Department of Earth Sciences
Research proposal
In the North Norfolk salt marshes the sediment is iron-rich and dominated by microbial communities that are reducing the iron while oxidising organic matter. Often there are areas of the salt marsh where the sediment beneath certain small ponds has accumulated an excess of organic matter and the pond has become sulfidic, full of hydrogen sulfide and dominated by microbial sulfate reduction. The pond sediment that has sulfide also has methane and this methane can escape through the rhizosphere and could be emitted to the atmosphere.
We are interested in the salt marsh sediments because they may be a good analogue for sediments that were deposited in oceans early in Earth history and therefore may hold clues for the geochemical and mineralogical signals that we might find in ancient rocks. Throughout the early part of Earth history, all ocean sediments were iron rich.
The student will be involved with collecting sediment core from the North Norfolk Marshes, separating out the layers of sediment and then doing analysis on the sediment mixtures as well as the pore fluids. These analyses will include mineralogical analysis involving X-ray diffraction and infrared spectroscopy (FTIR). The student will be involved with interpreting the IR spectra and understanding how the mineralogy of the sediment is changing. There will be an opportunity to then apply this to literature data of iron minerals extracted from ancient sedimentary rocks to compare one with the other. There may be the opportunity to also do iron speciation and isotope analysis on the various sediment fractions.
Professor Alexandra Turchyn is an environmental and isotope geochemist who studies the carbon cycle in sedimentary environments and across Earth's surface. She has been studying the Norfolk salt marshes as a model ecosystem for over a decade. Bizhou Zhu is a PhD student in the Turchyn lab and will be the day-to-day contact for the student. She is working on iron isotope analysis to understand the mineralogical changes when sediment undergoes diagenetic transformations.
Lead supervisor: Helen Williams, Department of Earth Sciences
Co-supervisor: Ross Findlay, Department of Earth Sciences
Research proposal
Context: The carbonaceous chondrite meteorites (CCs) are time capsules from the early Solar System that contain information pertaining to the accretion of the terrestrial planets and the evolution and distribution of water in the solar nebula [1]. Some of the original parent bodies — the asteroids from which these meteorites are sourced — originally bore an appreciable amount of water, accreted as a fraction of frozen water ice that subsequently melted due to the heat induced from radioactive decay [e.g., 2]. The water has since altered the mineralogy of these bodies, as sampled by meteorites, to include a high proportion of secondary minerals such as serpentines and carbonates.
Of particular interest are the CR, ‘Renazzo-type’ chondrites, which have long been thought to have formed in the outer Solar System at greater heliocentric distances to other CCs [3]. This is owed to their very elevated hydrogen isotopic composition in water and organic matter, which is equivalent to, or higher than that observed for comets [4]. Historically these meteorites have been rather rare; however, with an increase in the recovery of stones from hot deserts in North Africa, we are fortunate enough to possess a 51.9 g fragment of the CR chondrite Erg Chech 003, providing a large surface area to examine the petrographic relationships between its components.
Objectives: The intern will use Scanning Electron Microscopy (SEM) to petrographically characterise Erg Chech 003 by examining the texture and chemical composition of its constituent components that formed in the solar nebula. These include refractory calcium aluminium inclusions, chondrules (flash heated droplets of nebula dust), and the dusty, aqueously altered matrix that hold the specimen together. An additional focal part of the study will be to examine the polished blocks for any small, fine-grained clasts. These have been reported elsewhere and may be exogeneous fragments of comets [5]. Doing so will elucidate the nature and intensity of the aqueous alteration in Erg Chech 003, and by extension, its parent asteroid.
Methods: Following an initial settling / reading period (1 week) the intern will be trained how to sub sample the meteorite and make their own polished blocks by mounting them in resin followed by hand polishing (2 weeks). Following on will be a short SEM campaign to map and characterise the polished blocks using backscatter electron imaging and energy dispersive spectroscopy (2-4 sessions, 2 weeks). The data will then be processed offline to elucidate the degree of aqueous alteration (1 week), followed by interpretation and writing up the data into a report (2 weeks).
Expertise: Dr R. Findlay is a LCLU PDRA investigating aqueous alteration phenomena in carbonaceous chondrites, working with Professor Helen Williams.
Reading:
[1] Trigo-Rodríguez, J. M. et al., (2019). Space Science Reviews, 215, 1-27.
[2] Suttle, M., et al., (2021). Geochimica et Cosmochimica Acta, 299, 219-256.
[3] Schrader, D. L., et al., (2014) Earth and Planetary Science Letters, 407, 48-60.
[4] Bonal, L. et al., (2013). Geochimica et Cosmochimica Acta, 106, 111-133.
[5] Nittler, L. R. et al., (2019). Nature Astronomy, 3, 659-666.