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Planetary Habitability Inside and Out


Faculty of Environment

About the Project

Science Overview:

Life on Earth has persisted for billions of years and it is the only planet know to life. Mars and Venus may have been amenable to life in the past but cannot currently maintain an abundant biosphere. Thousands of exoplanets have been discovered, some in the `habitable zone’ of their host star; however, both Earth and Mars are in our habitable zone, so it is not clear whether detected exoplanets are truly habitable. The long-term habitability of a planet depends on the maintenance and interaction of many global-scale systems linking the atmosphere, hydrosphere, biosphere, and geosphere. One such interaction is the shielding that the global magnetic field provides against the solar wind, which otherwise acts to strip planets of their atmospheres, a process that may have played a key role in transforming Mars from a wet world to its current arid state. Traditionally, the evolution of the deep Earth has been considered separately from that of the surface environment and thus key questions remain. How important has magnetic shielding been for protecting Earth’s habitability? How has the slow evolution of the mantle and core impacted the strength of the geomagnetic field and hence the protection it provides from solar wind? Have those changes meaningfully impacted atmospheric bulk composition?

In this project, you will model the evolution of Earth’s interior and atmosphere over billions of years making use of VPLanet (Barnes et al., 2020), a software package that allows flexible investigation of planetary system evolution and habitability. Within VPLanet computational modules that account for different physical processes can be turned on or off and supplemented with relative ease. We have developed new models of the thermal evolution of Earth’s core (Greenwood et al., 2020) and how the power available to drive the dynamo relates to the strength of the geomagnetic field (Davies et al., 2020) that you will incorporate into the VPLanet framework. Atmospheric evolution is also influenced by surface geochemical cycles (Alcott et al., 2019; Rushby et al., 2018), which need to be included within VPLanet. Once these capabilities are incorporated into the modelling framework, you will explore a range of planetary evolutionary pathways to understand how changes in the deep interior of Earth (or other planets) alter planetary magnetic fields over geologically long-time scales and impact on habitability.

Paleomagnetism provides an observational check on the magnetic history of Earth. However, data uncertainties and gaps in the rock record allow a range of plausible paleointensity evolutions. By modelling the thermal evolution of the core and mantle you will generate a suite of possible magnetic histories for Earth. These histories will be used to determine the potential impact of magnetic variations on Earth’s atmosphere. To what extent would prolonged periods of weak magnetic field alter atmospheric composition due to enhanced solar wind stripping? Are such impacts compatible with geochemical records of atmospheric evolution? Thermal evolution of the Earth’s interior also plays a critical role in atmospheric redox and greenhouse gas evolution, which can be compared to geochemical records. On other planets, a broader range of scenarios are possible and the evolution of habitability on Mars or exoplanets can be explored.


Training Environment:

You will receive training in skills tailored to the project that are also useful for a future career as a research scientist in academia or elsewhere. You will be working as part of a large interdisciplinary team providing the opportunity to engage with related topics including: the structure, dynamics, and material properties of the deep Earth; global tectonic and biological processes; and how such processes can be tested with geochemical data. You will learn computational and mathematical methods to produce and analyse numerical results and the use of large-scale high-performance computing resources, including those at the University of Leeds (https://arc.leeds.ac.uk/). Alongside transferable skills in communication and project management, this can open a wide range of career pathways. Skills will be developed through hands-on experience, attending external training courses, and participating in the PANORAMA NERC doctoral training partnership.


Student Profile:

This project offers flexibility depending on your interests and experience, with a main focus on code development and the interactions between global-scale systems. Whatever your background, strong mathematical skills, curiosity and a desire to learn will be important.

Funding Notes

We offer 3.5 years fully funded studentships including full tuition fees for all successful applicants, and stipend at the UKRI rate plus a training grant.

References

1. Barnes, R., et al. (2020), VPLanet: The Virtual Planet Simulator, Publications of the Astronomical Society of the Pacific, 132(1008), 024502. doi: 10.1088/1538-3873/ab3ce8

2. Davies, C.J., Bono, R.K., Meduri, D.G., Greenwood, S. and Biggin, A.J. (2020) Dynamo constraints on the long-term evolution of Earth’s magnetic field strength, Under consideration in GJI.

3. Greenwood, S., Davies, C.J., and Mound, J.E. (2020) On the evolution of thermally stable layers at the top of Earth’s core, Under consideration in Physics of the Earth and Planetary Interiors, preprint:https://eartharxiv.org/bh43s/

4. Alcott, L. J., Mills, B. J. W. & Poulton, S. W. Stepwise Earth oxygenation is an inherent property of global biogeochemical cycling. Science 366, 1333-1337 (2019).

5. Rushby, A. J., Johnson, M., Mills, B. J. W., Watson, A. J. & Claire, M. W. Long-Term Planetary Habitability and the Carbonate-Silicate Cycle. Astrobiology 18, 469-480, doi:10.1089/ast.2017.1693 (2018).

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