DR CRAIG O'NEILL
ORIGINS RESEARCH INSTITUTE, CENTRE FOR ASTRONOMY AND
EARTH SCIENCE, HUNGARY

EARTH'S DYNAMICS
AND ITS FUTURE

TA L K O U T L I N E• Geodynamics: State ofplay• 3 frontiers• Approaches• Gap analysis androadmaps

S TAT E O F T H E
FIELD
Recent advances include• Supercomputing power - and moresophisticated 3D models• Rapidly advancing mineral physics

models• Ab initio molecular dynamics

simulations complementing existing
experimental approaches• Advances in detailed seismology ofthe Earth• Geoneutrino constraints

supplementing cosmochemical results

THREE FRONTIERS

1. THE FUTURE OF GEODYNAMICS T H E D E E P PA S T ?
•Origins of plate tectonics ca. 3 Gyr ago(eg. Hawkesworth and Cawood, 2018)

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Evolution of atmosphere and life
connected to tectonics (eg. O'Neill et al., 2013)
Core and geodynamo not understood
Exposed continental extent likely
changed dramatically (Kump and Barley, 2007)
Volcanism significant heat transportmechanism (Moore and Webb, 2013)
Impact bombardment likely an
important geodynamic driver in theHadean (O'Neill et al., 2017, 2020)

Evolution of modern tectonics cannot be understood
without context from the past

2. THE FUTURE OF GEODYNAMICS THE DEEP EARTH•••••••

Lower mantle is still poorly constrained
Mixture of largely Bridgmanite,
ferropericlase/magnesiowustite, and minor
phases like Al and Ca perovskite
Viscosity of these minerals has historically
been difficult to obtain (experimentalpressure, temperature and strain limits)
Ab initio calculations is starting to shed lighton thisBut bulk properties (viscosity) need mixing
models, which aren't well developedexperimentally
Complexities - iron spin transition at 1000kmD", LLSVP structures, and post-perovskite
behaviour3. THE FUTURE OF GEODYNAMICS THE FINAL FRONTIER•••••

Reasonably estimates suggest billions of planet's in the galaxy (let alone in the JWST
image shown)
A very small number have representatives in the solar system
Different inherited cosmochemistry, planetary formation pathways and system
histories (including radiogenic nuclides) (eg. Lugaro et al., 2014)
Very different heat budgets, mineral assemblages, volatile budgets (and thus ocean
to continent ratios - perhaps even ocean compositions)
Plausibly very different behaviours (O'Neill and Lenardic, 2007; Valencia et al., 2007)

HOW DO WE MODEL
THIS COMPLEXITY?

APPROACHES TO THIS DIVERSITYREDUCTIONIST APPROACH• Consider elements in problem and constrain them individually• Consider implications of effect in simple geodynamics models• Risks: Leaves out completing factors that may affect the impacts of individual components

COMPLEX SYSTEMS APPROACH• Treat geodynamics as an emergent phenomenon• Include the diversity of mechanisms, consider cascading complexity of processes• Identify emergent dynamics and priority parameters/processes• Risks: system rapidly becomes too complex to deconstruct/understandB E N C H M A R K I N G E M E R G E N T B E H AV I O U R S• Venus has no magnetic field and it has been suggested that it has no innercore• Plate motions, tectonics styles, • This has profound implications for it's cooling history - no inner core would

and geological constraints(Moresi and Solomatov, 1998; Tackley, 2001; O'Neillet al., 2013)• Heat flow and volcanism (Davies,2013; Rozel et al., 2015)• Global seismology and planet

structure (eg. Becker and Boschi (2002))• Geoid, length of day, andmoment of inertia (Rudolph et al., 2015)• An example: Venus - Earth'sTwin? Or Mercury's twin?

imply no plate tectonics• New constraints on Venus's moment of inertia (MoI, Margot et al., 2021),

together with mineral physics models (Burnman), allow assessment of possible
endmembers (see O'Neill, 2021 for details)• Venus either has no inner core (for an Earth-like composition), or a very largecore (R = 4000 km, inner core R=2000 km) for a Mercury-like "light element"enriched core composition. Need better cosmochemical or geophysicalmodels to constrain these possibilities

PROBING THE
EARTH
Advances in probing the Earth are covered in
upcoming talks, but briefly, there has beensignificant recent leaps in:• Cosmochemistry, heat flow and thermal

models, and neutrinos constraints on internal
elemental structure• Seismology• Experimental and ab initio MD calculations• Signi cant work is required though tofi

bridge the relevant scales inherent inthese advances.

PROBING OTHER WORLDS• Planetary geochemistry is related to stellar chemistry - somethingthat is observable. But a planets represents the end of a planetary
formation process, including volatile loss and fractionation ofelements, which is not a resolved problem and varies within thesolar system (eg. Sun and McDonough, 1989, Lodders, 2003).
• Significant cosmochemical variation exists between planets, andthus differences in bulk mineral composition (eg. between Mars vsEarth vs asteroids)• In the exoplanet catalogue even more chemical variation isexpected -> what sort of mineralogical variation is implied? This iscurrently unknown.

B E N C H M A R K I N G B E H AV I O U R S
We could (potentially) constrain exoplanet geodynamics from:• Atmospheric composition - volcanism, degassing and recycling are tied totectonics (and also geomicrobiology - see Kastings 2010). But - diagnostic
atmospheric signals of plate tectonics not clear. Needs coupledgeodynamics - volcanic - degassing - atmosphere models.
• Geoid, gravity, size and moment of inertia -> these can constrain heat(internal temperatures), internal composition and/or tradeoffs between
them• Length of day changes? 2004 Sumatra earthquake changed the LoD by 2.68

microseconds, and shifted the pole by 2.5 cm. This is remotely detectablefrom rotation. Technically, very challenging - but not impossible!

T H E S TAT E O F T H E F I E L D• Large advances in computational power and approaches, and enhancements in understanding

high-pressure mineral physics.
• Critical frontiers in deep time, deep planetary interiors, and exoplanetary tectonics• What is needed is a formal gap analysis, and a roadmap forward• Some initiatives already underway:• Community codes (eg. https://geodynamics.org/)• Community rheology models• Computational resources (currently sourced locally, using national facilities, or commercially(eg. AWS)).
• Observational test and data archive (eg. https://ggos.org/item/global-gravity-field-models/,

https://www.ngs.noaa.gov/GEOID/, https://shtools.github.io/SHTOOLS/python-datasetsconstants.html, https://pds.nasa.gov/).