Geology’s great divide

Geology’s great divide

It’s reassuring to see that the incoming generation of undergraduate science students is environmentally minded. But unfortunately, some students are being steered away from the study of geology – perhaps because they associate the discipline with the extraction of fossil fuel resources.

Clearly, making the transformation to a sustainable, low-carbon society is the “next big thing” facing our planet. In fact, geology has a central part to play in this transition by enabling the sourcing and extraction of the critical minerals needed for green technologies, such as solar panels and the batteries that power electric vehicles, as outlined (for example) by the Geoscience for the Future poster of The Geological Society, London.

The next big thing in my particular field? That’s making sure that Australia trains the geologists we will need to fill these roles. Australia’s mineral reserves are estimated to be the second largest in the world for copper (used in wiring and some solar panel cells, and for which supply barely meets demand) and lithium (used in rechargeable batteries), and sixth largest in the world for rare earth elements (used in the batteries of electric vehicles and in magnets in wind turbines), although this latter resource remains largely untapped.

Geology has a central part to play by enabling the sourcing and extraction of the critical minerals needed for green technologies.

We need trained geologists to locate and extract these resources so they can do their bit for the environment and our planet’s future and become part of the change to a greener economy. As a bonus, geologists get to study the 4.5 billion-year history of our planet – which certainly puts our species’ existence into perspective: how astonishing that Homo Sapiens have only roamed Earth’s surface for 200,000 years or so.

Our “laboratory” is Earth itself. I have always loved being out in nature. Growing up in Europe, my family would go on bushwalks to enjoy the wonders of the natural world, and while we all loved living things, we would spend more time than most families looking at rocks – as you do when both parents are geologists. Volcanoes, both extinct and live, were also a destination of choice for our vacations, and I have vivid memories of the smell of sulphur when we visited Stromboli, and of being mesmerised by a lava flow slowly swallowing up a small tree at dusk down in a gully on a flank of Mount Etna.

Our “laboratory” is Earth itself.

Perhaps it was these experiences that sharpened my sense of curiosity? It could explain why I decided that I wanted to be a researcher in the sciences by age 15. As a teenager, I wanted to be different from my parents, but when given a choice between molecular biology or geology two years into my undergraduate studies, I picked the latter without much hesitation knowing it would involve field work – out in nature.

As a PhD student I was lucky to research the history of the solid Earth and its influence on Earth’s surface. By considering the slow cooling of the interior of the planet and the growth of the continental crust, I was able to model the evolution of sea levels over the history of the planet.

The original idea came from one of my supervisors, who suggested we investigate whether mid-ocean ridges, a 60,000km-long chain of submarine volcanoes that wraps about one and a half times around Earth’s surface, could have been emerged early in the planet’s history – if so, it would have profoundly changed the composition of Earth’s atmosphere. But we found this scenario to be unlikely. Instead, our models suggested that two billion years ago, global sea levels could have been about one kilometre higher than at present; our planet could have been a “water world” in which the emerged land surface would only be approximately that of North and South America combined. These results were consistent with geological and geochemical observations that suggest that the continents could have emerged two billion years into the planet’s history and triggered the first global accumulation of oxygen in the atmosphere by delivering nutrients to primitive photosynthetic life forms called stromatolites.

Naturally, the model we proposed is a necessary simplification of our complex planet, and the scenario of a water world during the first half of the history of our planet is not unequivocal. But the main contribution of my PhD work was probably to have challenged the previous consensus that sea level had not significantly varied over the history of the planet. Looking back, I can now see that this was a bold topic for a PhD thesis, one that I might not have pursued had I not been so ingenuous.

Our island continent came together hundreds of millions of years ago and has not been affected by recent collisions of tectonic plates.

As a postdoctoral researcher, I worked as part of a team to reconstruct the evolution of the Earth’s mantle – the solid rock layer of the planet that extends down to 3,000km depth – over the past 250 million years. This was done by coupling the past position and motion of tectonic plates with convection models. I investigated how the motion of tectonic plates and convective motion deep within the Earth affect topography at the scale of continents: cold oceanic lithosphere pulls Earth’s surface down as it sinks into the mantle, whereas hot mantle pushes the surface up as it rises. Australia is a world-class natural laboratory to study this phenomenon called dynamic topography because our island continent came together hundreds of millions of years ago and has not been affected by recent collisions of tectonic plates. I was part of a team that showed how mantle convection contributed to shaping the Australian landscape and river network, causing much of the eastern part of the continent to be covered by an inland sea up to 100 million years ago and being a driving force behind the rise of the Great Dividing Range.

Mantle convection also affects global topography, and some of my forthcoming work shows that the assembly of Pangea caused mantle upwelling below the supercontinent, resulting in low sea levels.  A hot research question in geodynamics is whether continent-sized hot structures at the base of the mantle under Africa and the Pacific Ocean acted as stationary anchors for global tectonic motions over time. To contribute to this debate, I am using tectonic reconstructions extending back to one billion years ago to investigate the link between the configuration of continents, large volcanic eruptions, and the structure of the deep mantle.

That might not sound like the “next” big thing, but it’s this kind of understanding of our planet that just might help save it.

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