Geology Bites

As we wean ourselves away from fossil fuels and ramp up our reliance on alternatives, batteries become ever more important for two main reasons. First, we need grid-scale batteries to store excess electricity from time-varying sources such as wind and solar. Second, we use them to power electric vehicles, which we are now producing at the rate of about 15 million a year worldwide.

So far, the battery of choice is the lithium-ion battery. In addition to lithium, these rely on four metals — copper, nickel, cobalt, and manganese. In the podcast, Adam Simon explains the role these metals play in a battery. He then describes the geological context and origin of the economically viable deposits from which we extract these metals.

Simon is a professor of economic geology at the University of Michigan.

Knowing exactly where faults are located is important both for scientific reasons and for assessing how much damage a fault could inflict if it ruptured and caused an earthquake. In the podcast, Rufus Catchings describes how we can use natural and artificial sources of seismic waves to create high-resolution images of fault profiles. He also explains how faults can act as seismic waveguides, an effect that enables us to determine whether faults are connected to each other. In Napa, a famous wine-growing area near San Francisco, he used guided waves to determine that an active fault is actually ten times longer than previously thought.

During the past couple of decades, we have discovered that stars with planetary systems are not rare, exceptional cases, as we once assumed, but actually quite commonplace. However, because exoplanets are like fireflies next to blinding searchlights, they are incredibly difficult to study. Yet, as Sara Seager explains, we are making astonishing progress. Various ingenious methods and the use of powerful space telescopes enable us to learn about exoplanet atmospheres and even, in some cases, what their surfaces consist of.

Sara Seager’s research concentrates on the detection and analysis of exoplanet atmospheres, and she has just won the prestigious Kavli Prize for this work. She has had leadership roles in space missions designed to discover new exoplanets and find Earth analogs orbiting a sun-like star. She is a Professor of Aeronautics and Astronautics, Professor of Planetary Science, and Professor of Physics at the Massachusetts Institute of Technology.

We have only a tantalizingly small number of sources of information about the Earth’s deep mantle. One of these comes from the rare diamonds that form at depths of about 650 km and make their way up to the base of the lithosphere, and then later to the surface via rare volcanic eruptions of kimberlite magma. In the podcast, Evan Smith talks about a new class of large gem-quality deep-mantle diamonds that he and his coworkers discovered in 2016. Inclusions within these diamonds serve as messenger capsules from the deep mantle. They show an unmistakable genetic link to subducted oceanic slabs, and thus give us clues as to what happens to subducted slabs as the pass through the lower mantle transition zone.

Evan Smith is a Senior Research Scientist at the Gemological Institute of America, New York.

Continental crust is derived from magmas that come from the mantle. So, naively, one might expect it to mirror the composition of the mantle. But our measurements indicate that it does not. Continental crust contains significantly more silica and less magnesium and iron than the mantle. How can we be sure this discrepancy is real, and what do we think explains it? In the podcast, Roberta Rudnick presents our current thinking about these questions. Surprisingly, more than 30 years after she and others first identified the so-called continental crustal composition paradox, there is still no consensus among geologists as to which of the many proposed hypotheses most convincingly solves the paradox.

We tend to think of continental tectonic plates as rigid caps that float on the asthenospheric mantle, much like oceanic plates. But while some continental regions have the most rigid rocks on the planet, wide swathes of the continents are not rigid at all. In the podcast, Alex Copley explains how this differentiation comes about and points to evidence that the responsible processes have been operating since the Archean.

Shanan Peters believes we need to assemble a global record of sedimentary rock coverage over geological time. As he explains in the podcast, such a record enables us to disentangle real changes in the long-term evolution of the Earth-life system from biases introduced by the unevenness and incompleteness of the sedimentary record. To this end, he and his team have established Macrostrat, a platform for the aggregation and distribution of our knowledge about the spatial and temporal distribution of sedimentary rocks. In the podcast, he describes some important findings made possible by Macrostrat. One of them is that gaps in the record are often as revealing about the underlying processes involved as the rocks preserved above and below the gaps.

Peters is a Professor in the Department of Geoscience at the University of Wisconsin-Madison.

Complex life did not start in the Cambrian - it was there in the Ediacaran, the period that preceded the Cambrian. And the physical and chemical environment that prevailed in the early to middle Cambrian may well have arisen at earlier times in Earth history. So what exactly was the Cambrian explosion? And what made it happen when it did, between 541 and 530 million years ago? Many explanations have been proposed, but, as Paul Smith explains in the podcast, they tend to rely on single lines of evidence, such as geological, geochemical, or biological. He favors explanations that involve interaction and feedback among processes that stem from multiple disciplines. His own research includes extensive study of a site where Cambrian fossils are exceptionally well preserved in the far north of Greenland.

Smith is Director of the Oxford University Museum of Natural History and Professor of Natural History at the University of Oxford.

Jupiter's innermost Galilean moon, Io, is peppered with volcanos that are erupting almost all the time. In this episode, Scott Bolton, Principal Investigator of NASA's Juno mission to Jupiter, describes what we're learning from this space probe.

Since its arrival in 2017, its orbit around the giant planet has progressively shifted to take it close to Jupiter’s moons and rings. In December 2023 and February 2024, it flew by Io, approaching within a distance of only 1,500 km. This enabled Juno to capture high-resolution imagery of its constantly changing surface, including hitherto unseen regions near its poles. As discussed in the podcast, Juno is equipped with a microwave instrument that enables it to look slightly below the moon’s surface into its lava lakes, as well as a suite of magnetometers to study Jupiter’s giant magnetosphere and its remarkable interaction with Io.

Bolton’s research focuses on Jupiter and Saturn and the formation and evolution of the solar system. Prior to the Juno mission, he led a number of science investigations on the Cassini, Galileo, Voyager, and Magellan missions. He is Director of the Space Sciences Department at Southwest Research Institute in San Antonio, Texas.

We know that most magma originates in the Earth’s mantle. As it pushes up through the many kilometers of lithosphere to the surface, it pauses in one or more magma chambers or partially melted mush zones for periods of up to a few millennia before erupting. But while we have seismic evidence and models and support this picture, we have not hitherto been able to watch how magma actually moves in the upper mantle and crust.

Bob White has set out to change that. Using a dense array of seismometers, he has been able to pinpoint thousands of tiny earthquakes that reveal the detailed movement of melt through the thick crust of Iceland just before it erupted. White combines this seismic data with geochemical analyses of the lava that can tell us about the depths at which the melt is formed.

White is Emeritus Professor of Geophysics in the Department of Earth Sciences at the University of Cambridge.