Geology Bites By Oliver Strimpel

From East Africa to southwest USA, many regions of the Earth's continental lithosphere are rifting. We see evidence of past rifting along the passive margins of continents that were once contiguous but are now separated by wide oceans. How does something as apparently solid and durable as a continent break apart?In the podcast, Folarin Kolawole describes the various phases of rifting, from initial widespread normal faulting to the localization of stretching along a rift axis, followed by rapid extension and eventual breakup and formation of oceanic lithosphere.Kolawole is especially interested in the early stages of rifting, and in his research he uses field observation, seismic imaging, and mechanical study of rocks. He is Assistant Professor of Earth and Environmental Sciences, Seismology, Geology, and Tectonophysics at the Lamont-Doherty Earth Observatory of Columbia University.

Most of Earth's salt is dissolved in the oceans.  But there is also a significant amount of solid salt among continental rocks.  And because of their mechanical properties, salt formations can have a dramatic effect on the structure and evolution of the rocks that surround them.  This gives rise to what we call salt tectonics – at first sight, a rather surprising juxtaposition of a soft, powdery substance with a word that connotes the larger scale structure of the crust.In the podcast, Mike Hudec explains the origin of salt in the Earth's crust and describes the structures it forms when subjected to stresses. He also discusses how salt can play in important role in the formation of oil and gas reservoirs.Hudec is a research professor at the Bureau of Economic Geology at the University of Texas at Austin.

Megafloods are cataclysmic floods that are qualitatively different from weather-related floods. In the podcast, Vic Baker explains our ideas as to what causes megafloods and describes the striking evidence for such floods in the Channeled Scablands of Washington State and in the Mediterranean.Vic Baker has been studying megafloods for over 50 years.  He is a Professor of Hydrology and Atmospheric Sciences, Geosciences, and Planetary Sciences at the University of Arizona.

The planets formed out of a cloud of gas and dust around the nascent Sun. Within the so-called snow line, it was too hot for liquid water to exist. Since the Earth lies well within this line, why does it have water? Did it somehow manage to retain water from the outset or did it acquire its water later? In the podcast, Lindy Elkins-Tanton explains how these two scenarios might have played out but she says the evidence strongly favors one of these theories. Elkins-Tanton has concentrated much of her research career on the formation and evolution of planets, and especially the role of water. She is a Professor in the School of Earth and Space Exploration at Arizona State University and Principal Investigator of the NASA Psyche mission.

Golden spikes are not golden, nor are they generally spikes. So what are they, and, more importantly, what exactly do they represent? In the podcast, Joeri Witteveen explains how we arrived at our present system of defining the boundaries of stages in the rock record with a single marker. Paradoxically, it turns out that the best place for a golden spike is where “nothing happens.” Listen and find out why.Witteveen is Associate Professor of History and Philosophy of Science at the University of Copenhagen.

The late Paleozoic ice age began in the Late Devonian and ended in the Late Permian, occurring from 360 to 255 million years ago. It was similar to the present day in two key respects: rising atmospheric CO2 and recurrent major ice sheets. In the podcast, Isabel Montañez explains how we can use proxies to learn about the climate and ocean conditions that prevailed then. And with the help of a model, she says that we can also learn about sensitivities and feedbacks of Earth systems to rising CO2. Among other things, the model suggests that when the atmosphere reaches the present day level of CO2, significant parts of the ocean may become anoxic and ocean circulation patterns alter.Montañez is a Distinguished Professor in the Department of Earth and Planetary Sciences at the University of California, Davis.

At first sight, urban geology sounds like an oxymoron.  How can you do geology with no rocky outcrops anywhere in sight within the built-up environments of cities?  It turns out you can do a great deal of geology, and Ruth Siddall has been doing just that for the past 10 years. In the podcast, she describes some of the many aspects of geology, from petrology to paleontology, that can be seen very clearly in building stone. She also takes us on a walking tour in London from the Monument to the Great Fire of London to the Tower of London.Siddall has developed nearly 50 urban geology-themed walks and built up a database of over 4,300 urban localities of geological interest. She is a postdoctoral researcher at Trinity College, Dublin, studying the social history and geological provenance of stone in 18th century buildings in Britain and Ireland.

The Earth is about 4.5 billion years old. How can we begin to grasp what this vast period of time really means, given that it is so far beyond the time scale of a human life, indeed of human civilization? Richard Fortey has devoted his long and prolific research career at the Natural History Museum in London to the study of fossils, especially the long-extinct marine arthropods called trilobites.  In an earlier episode of Geology Bites, he talked about measuring time with trilobites. In this episode, he describes how it was the fossils in the geological record that gave us the first markers along the runway of deep time, providing the structure and language within which our modern conception of deep time emerged.

The Himalaya are just one, albeit the longest and highest, of several mountain ranges between India and Central Asia. By world standards, these are massive ranges with some of the highest peaks on the planet.  The Karakoram boasts four of the world's fourteen 8,000-meter peaks, and the Hindu Kush, the Pamir, the Kunlun Shan, and the Tien Shan each have many peaks above 7,000 meters.  No mountain ranges outside this region have such high mountains.  Yet we seldom hear much about these ranges.  In the podcast, Mike Searle describes the origin and geology of six central Asian ranges and how they relate to the Himalaya and the collision of India with Asia. India continues to plow into Asia to this day. How is this movement accommodated? Searle explains the extrusion and crustal shortening models that have been proposed and describes the detailed mapping he and his colleagues conducted in the field in northern India that showed that both mechanisms are operating. Searle is Emeritus Professor of Earth Sciences at the University of Oxford.

The Caledonian orogeny is one of the most recent extinct mountain-building events. It took place in several phases during the three-way collision of continental blocks called Laurentia, Baltica, and Avalonia during the early stages of the assembly of the supercontinent Pangea. In the process, Himalayan-scale mountains were formed. While these mountains have been worn down today, we still see plenty of evidence for their existence in locations straddling the Atlantic and the Norwegian Sea. In the podcast, Rob Strachan describes the tectonic movements that led to the orogen and explains how we can reconstruct the sequence of events that occurred and what we can learn about today's mountain-forming processes by studying the exhumed rocks of ancient orogens. Strachan has studied the rocks of the Caledonian orogen for over 40 years, focusing on unraveling the history of the orogen in what is Scotland today.  He is Emeritus Professor of Geology at the University of Portsmouth.

With most of Greenland buried by kilometers of ice, obtaining direct information about its geology is challenging. But we can learn a lot from measurements of the island's geophysical properties — seismic, gravity, magnetic from airborne and satellite surveys and from its topography, which we can see relatively well through the ice using radar. In the podcast, Joe MacGregor explains how he created a new map of Greenland's geology and speculates on what we can learn from it. MacGregor is a Research Physical Scientist at NASA's Goddard Space Flight Center.

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. Rufus Catchings is a Research Geophysicist at the US Geological Survey (USGS). Over the past 40 years, he has studied many dozens of faults in California and elsewhere to pin down their precise locations and help assess the risks they pose.

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. Rudnick is a Distinguished Professor in the Department of Earth Science at the University of California Santa Barbara.

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. Copley is Professor of Tectonics in the Department of Earth Sciences at the University of Cambridge.

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 the 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 it 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.

At roughly 15-25-million-year intervals since the Archean, huge volumes of lava have spewed onto the Earth's surface. These form the large igneous provinces, which are called flood basalts when they occur on continents. As Richard Ernst explains in the podcast, the eruption of a large igneous province can initiate the rifting of continents, disrupt the environment enough to cause a mass extinction, and promote mineralization that produces valuable mineral resources. Richard Ernst studies the huge volcanic events called Large Igneous Provinces (LIPs) — their structure, distribution, and origin as well as their connection with mineral, metal, and hydrocarbon resources; supercontinent breakup; and mass extinctions. He has also been studying LIP planetary analogues, especially on Venus and Mars. He has written the definitive textbook on the subject. Ernst is Scientist in Residence in the Department of Earth Sciences, Carleton University, Ottawa, Canada, and Professor in the Faculty of Geology and Geography at Tomsk State University, Tomsk, Russia.

Perhaps as many as five times over the course of Earth history, most of the continents gathered together to form a supercontinent. The supercontinents lasted on the order of a hundred million years before breaking apart and dispersing the continents. For decades, we theorized that this cycle of amalgamation and breakup was caused by near-surface tectonic processes such as subduction that swallowed the oceans between the continents and upper mantle convection that triggered the rifting that split the supercontinents apart. As Damian Nance explains in the podcast, newly acquired evidence suggests a very different picture in which the supercontinent cycle is the surface manifestation of a process that involves the entire mantle all the way to the core-mantle boundary. Damian Nance draws on a wide range of geological evidence to formulate theories about the large-scale dynamics of the lithosphere and mantle spanning a period going back to the Archean. A major focus of his research is the supercontinent cycle. He is Distinguished Professor Emeritus of Geological Sciences at Ohio University.

The Earth's tectonic plates float on top of the ductile portion of the Earth's mantle called the asthenosphere. The properties of the asthenosphere, in particular its viscosity, are thought to play a key role in determining how plates move, subduct, and how melt is produced and accumulates. We would like to know what the viscosity of the the asthenosphere is, and how it depends on temperature, pressure, and the proportion of melt and water it contains. Few mantle rocks ever reach the Earth's surface, and those that do are altered by weathering. So, as he explains in the podcast, David Kohlstedt and his team have tried to replicate the rock compositions and physical conditions of the mantle in the lab. Using specially-built apparatus, he has been able to determine the viscosity of the asthenosphere to within an order of magnitude, which is an enormous improvement on what was known before. David Kohlstedt is Professor Emeritus at the School of Earth and Environmental Science at the University of Minnesota.

In many countries, nuclear power is a significant part of the energy mix being planned as part of the drive to achieve net-zero greenhouse-gas emissions. This means that we will be producing a lot more radioactive waste, some of it with half-lives that approach geological timescales, which are orders of magnitude greater than timescales associated with human civilizations. In the podcast, Claire Corkhill discusses the geology such storage sites require, some new materials that can confine radioactive isotopes over extremely long timescales, and the kind of hazards, including human, we need to guard against. Claire Corkhill is Professor of Mineralogy and Radioactive Waste Management in the School of Earth Sciences at the University of Bristol, UK.

We have learned a great deal about the geology of the Moon from remote sensing instruments aboard lunar orbiters, from robot landers, from the Apollo landings, and from samples returned to the Earth by Apollo and robot landings. But in 2025, when NASA plans to land humans on the Moon for the first time since 1972, a new phase of lunar exploration is expected to begin. What will this mean for our understanding of the origin, evolution, and present structure of the Moon? A lot, according to Mahesh Anand. For example, as he explains in the podcast, satellite imagery suggests that volcanism continued for much longer than was previously thought, perhaps until as recently as 100 million years ago. In-situ inspection and sample return should help us explain this surprising finding. Mahesh Anand is Professor of Planetary Science and Exploration at the Open University, UK.

At the core of Earth's geological thermostat is the dissolution of silicate minerals in the presence of atmospheric carbon dioxide and liquid water. But at large scales, the effectiveness and temperature sensitivity of this reaction depends on geomorphological, climatic, and tectonic factors that vary greatly from place to place. As described in the podcast, to predict watershed-scale or global temperature sensitivity, Susan Brantley characterizes these factors using the standard formula for the temperature dependence of chemical reaction rates using an empirically-determined activation energy for each process. Overall, her results suggest a doubling of the weathering rate for each 10-degree rise in temperature, but this value changes with the spatial scale of the analysis. Susan Brantley is a Professor in the Department of Geosciences at Pennsylvania State University.

Banded Iron Formations (BIFs) are a visually striking group of sedimentary rocks that are iron rich and almost exclusively deposited in the Precambrian. Their existence points to a major marine iron cycle that does not operate today. Several theories have been proposed to explain how the BIFs formed. While they all involve the precipitation of ferric (Fe3+) iron hydroxides from the seawater via oxidation of dissolved ferrous (Fe2+) iron that was abundant when the oceans contained very low levels of free oxygen, they disagree as to how this oxidation occurred. In the podcast, Clark Johnson describes how oxidation could have occurred without the presence of abundant free oxygen in the oceans. Clark Johnson is a Professor Emeritus in the Department of Geoscience at the University of Wisconsin-Madison.

The geological history of most regions is shaped by a whole range of processes that occur at temperatures ranging from above 800°C to as low as 100°C. The timing of events occurring over a particular temperature range can be recorded by a mineral which crystallizes over that range. The mineral calcite is suitable for recording low-temperature processes such as fossilization, sedimentation, and fluid flow, and it is especially useful as it is virtually ubiquitous. But using uranium-lead radiometric dating in calcite is very challenging as it often contains very little uranium and the ragiogenically-produced lead isotopes can be swamped by common lead within a calcite crystal. In the podcast, Catherine Mottram explains how these challenges are being overcome and shares some of her findings based on radiometric dating of calcite. Mottram is an Associate Professor of Geology at the University of Portsmouth. 

In this episode, Martin Van Kranendonk lays out a convincing case for life on Earth going back to at least 3.48 billion years ago. To find evidence for very ancient life, we need to look at rocks that have been largely undisturbed over billions of years of Earth history. Such rocks have been found in the Pilbara region of northwest Australia. As explained in the podcast, the 3.48-billion-year-old (Ga) rocks of the Pilbara's Dresser Formation contain exceptionally well-preserved features that show unmistakeable physical and chemical signatures of life. While older 3.7 Ga rocks in west Greenland may also prove to have harbored life, the Dresser Formation rocks represent the oldest widely accepted evidence for life on Earth. Martin Van Kranendonk has devoted his long and prolific research career to the study of the early Earth. One major theme of his work has been to use detailed mapping and lab research to develop geological models for the environments of Earth's oldest fossils. This has helped establish the biological origin of many ancient fossils. His recent work on a newly discovered find of exceptionally well-preserved 3.5-billion-year-old sedimentary rocks in the Pilbara Craton of Western Australia has provided the strongest evidence to date that structures of this great age were produced by the earliest forms of life. Martin Van Kranendonk is a Professor in the School of Biological, Earth, & Environmental Sciences at the University of New South Wales in Sydney.

The Alps are the most intensively studied of all mountain chains, being readily accessed from the geological research centers of Europe. But despite this, there remains considerable uncertainty as to how they formed, especially in the Eocene (about 40 million years ago) when the events that led directly to Alpine mountain-building started. In the podcast, Rob Butler explains how much of this uncertainty stems from our fragmentary knowledge of the locations and structures of sedimentary basins and small continental blocks that lay between Europe and Africa at that time. In his research, he combines detailed studies of the sedimentary rocks flanking the Alps with the large body of structural and petrological knowledge amassed over the past two centuries to try to unravel the sequence of events leading up to the formation of the Alps. Rob Butler is Professor of Tectonics at the University of Aberdeen, Scotland, UK.

The Franciscan Complex is a large accretionary prism that has been accreted onto the western margin of the North American continent. Unlike most such prisms, which are submarine, it is exposed on land, making it a magnet for researchers such as John Wakabayashi. In the podcast, he describes this remarkable complex and explains the mechanisms that may have operated over its 150-million-year history. John Wakabayashi is a Professor in the Department of Earth and Environmental Sciences at California State University, Fresno. He has devoted much of his 40-year research career to the Franciscan Complex.

How can we tell if the sedimentary record is good enough to make solid inferences about the geological past? After all, it can be difficult, or even impossible, to infer what is missing, or indeed whether anything is missing at all. As he explains in the podcast, Bruce Levell tackles this question by combining fieldwork with systematic analysis based on what we know about contemporary deposition and erosion. Armed with an understanding of preservational bias, he questions the confidence with which some widely held interpretations of the sedimentary record have been made. For example, by analyzing sequences of glacially-deposited rocks in southwest Scotland, he has shown with others that, contrary to the “Hard Snowball Earth” hypothesis, parts of the Earth probably experienced a persistently active hydrological cycle and were not simply fully-frozen, at least during the earlier of the two postulated snowball glaciations. Bruce Levell is a Visiting professor in the Department of Earth Sciences at the University of Oxford. Previously, he was Chief Scientist for Geology at Royal Dutch Shell.

In a recent episode, Nadja Drabon spoke about newly discovered zircon crystals that formed during the late Hadean and early Archean, when the Earth was between 500 million and a billion years old.  The zircons revealed information about processes occurring in the Earth's nascent crust, casting light on when and how modern-day plate tectonics may have started.  In this episode, we talk about a very different source of information about the early Earth, namely the abundances of noble gases occurring within present-day basalts.  It turns out that these can probe the Earth's mantle and atmosphere even further back in time – to the first 100 million years of Earth history. Sujoy Mukhopadhyay leads a team of researchers who have developed new techniques for measuring the abundances of noble gas isotopes in a variety of Earth materials.  By combining the results of these measurements with geochemical models, he has shed light on questions about the very early Earth and planet formation that have challenged researchers for decades.  Here we focus on one of these: “Do any structures originating from the very early Earth survive in today's mantle?” Amazingly, the answer is "yes." Sujoy Mukhopadhyay is Professor of Geochemistry at the University of California, Davis.

In 2011, a massive earthquake struck off the eastern coast of Japan. The destructive power of the earthquake was amplified by a giant tsunami that swept ashore, killing over 15,000 people. A major cause of the tsunami was the 50-m slip along the plate boundary fault between the subducting Pacific plate and the overriding North American plate. Patrick Fulton and his team set out to find out why there was so much movement along the fault by installing a temperature observatory in a borehole drilled right through the fault zone. Patrick Fulton uses observation, quantitative analysis, and numerical modeling to study heat and fluid in fault zones. He applies his research to the physics of earthquakes, tectonic processes, and the transport of subsurface heat and fluids. In the podcast, he describes how he and his team installed a borehole temperature observatory below 7 km of ocean. The observatory detected the remnants of frictional heating generated by the slip that caused the 2011 Tōhoku Earthquake and the devastating tsunami that led to the Fukushima nuclear disaster. Patrick Fulton is an Assistant Professor in the Department of Earth and Atmospheric Sciences at Cornell University. For more about Geology Bites and illustrations that support the podcast, go to geologybites.com.

Romain Jolivet studies active faults and the relative motion of tectonic plates. His research focuses on the relationship between slow, aseismic slip that occurs “silently” between earthquakes and the rapid slip accompanying earthquakes. As he describes in the podcast, he uses interferometric synthetic aperture radar (InSAR) images from radar satellites to examine surface deformation over wide areas at meter-scale resolution. InSAR images of the 2023 Turkey-Syria earthquakes reveal complicated slip patterns occurring on well-recognized plate boundary faults as well as on hitherto ignored faults. Romain Jolivet is a Professor of Geoscience at the École normale supérieure in Paris. For illustrations that support this episode and to learn more about Geology Bites, go to geologybites.com.

The geological record shows that the Earth's carbon cycle suffered over 30 major disruptions during the Phanerozoic. Some of the biggest ones were accompanied by mass extinctions. Dan Rothman analyzed these disruptions to find a pattern governing their magnitude and duration. As he explains in the podcast, this pattern is suggestive of a non-linear dynamical system that, once excited, undergoes a large excursion before returning to where it was. Could we be exciting such a disruption now? He shows that the mass of anthropogenic carbon emissions forecast by the end of the century is about the same as the mass of carbon dioxide outgassed by the massive volcanism that generated the portion of the Deccan Traps deposited just before the end-Cretaceous extinction. This leads him to hypothesize that, while the Chixclub meteor impact may have been the direct cause of the extinction, the disruption of the carbon cycle caused by the outgassing of CO₂ during this prolific series of eruptions contributed to the environmental change associated with mass extinction. Go to https://www.geologybites.com/ for illustrations that support this episode and to learn more about the Geology Bites.

Vanishingly few traces of the early Earth are known, so when a new source of zircon crystals of Hadean age is discovered, it makes a big difference to what we can infer about that eon. In the podcast, Nadja Drabon describes how she analyzed the new zircons she and her colleagues discovered and what they reveal about the Earth's crust between about 4 and 3.6 billion years ago. Nadja Drabon's research aims to unravel the processes that formed the Earth's earliest crust. She does this by studying extremely ancient zircons. These are few and far between, so the discovery of a new source of such zircons in the Barberton Greenstone Belt of South Africa was exciting to early Earth researchers. In the podcast, she describes how she and her team used these zircons to discern a significant change in crustal processes about 3.8 billion years ago when much more fresh crust began to form. Nadja Drabon is Assistant Professor of Earth and Planetary Sciences at Harvard University. For podcast illustrations and more about Geology Bites, go to geologybites.com.

Over the course of Earth history, many parts of the crust have undergone multiple episodes of metamorphism. Modern methods of dating and measuring trace-element abundances are now able to tease out the timing and conditions of the individual episodes. But new techniques were needed before these methods could be scaled up to unravel regional tectonic events such as the formation of mountain belts and subduction zones and continental rifting. In the podcast, John Cottle describes one such technique that he and his group developed and that ushered in a revolution in the study of metamorphic rocks. He discusses how the technique was used to resolve the multiple phases of metamorphic history in the Himalaya, Antarctica, and New Zealand. John Cottle is a Professor in the Department of Earth Science at the University of California, Santa Barbara. Go to geologybites.com for illustrations that support the podcast and to learn more about Geology Bites.

This episode is the second of two of my conversation with Martin Gibling. In the first episode, we discuss fluvial deposits in the geological record and we trace the effect that the break-up of Pangea around 200 million years ago had on river systems. In this episode, we address the history of the rivers of Europe and the Americas, as well as the impact of the recent ice ages on today's rivers. We end by considering how humans have changed rivers and their deposits throughout mankind's history. Martin Gibling has spent a lifetime studying rivers and river sediments around the world. He is Emeritus Professor in the Department of Earth and Environmental Sciences at Dalhousie University in Halifax, Nova Scotia in Canada.

Rivers can seem very ephemeral, often changing course or drying up entirely. Yet some rivers have persisted for tens or even hundreds of millions of years, even testifying to the breakup of Pangea, the most recent supercontinent, about 200 million years ago. On the one hand, their courses may be determined by tectonic processes such as the formation of mountain belts. And on the other, they themselves can affect tectonic processes by creating continent-scale features, such as giant submarine fans. Martin Gibling has spent a lifetime studying rivers and river sediments around the world. He is Emeritus Professor in the Department of Earth and Environmental Sciences at Dalhousie University in Halifax, Nova Scotia in Canada. This episode is the first of two of our conversation about rivers. In this episode we talk about fluvial deposits in the geological record and the impact of the break-up of Pangea on river systems. In the second episode we talk specifically about the history of the rivers of Europe and the Americas, as well as the impact of recent ice ages. We end by considering how humans have changed rivers and their deposits throughout human history.

This episode is a bit of a departure from the objective approach to geology of past episodes in that here we address the subjective nature of various rocks as experienced by a rock climber with a literary bent. A rock climber's very survival can depend on the properties of a rock encountered along a climbing route. This engenders a uniquely intense relationship between climber and rock. Anna Fleming has written perceptively about this intense relationship gained from climbing in Britain and the Mediterranean. In a book entitled Time on Rock, she writes about her experiences climbing gritstone in England's Peak District, slate in the disused slate quarries of North Wales, gabbro and granite on the Isle of Skye, sandstone on the northeast coast of Scotland, and limestone cliffs on the Greek island of Kalymnos, among others.

Between 1.3 and 1.1 billion years ago, magma from the Earth's mantle intruded into a continent during the assembly of the supercontinent called Nuna. Through good fortune, the dykes and central complexes that resulted have been preserved in near-pristine condition in what is now the south of Greenland. The dykes are extraordinarily thick, and the central complexes contain an order of magnitude more exotic minerals than otherwise similar complexes around the world. In the podcast, Brian Upton describes what he found during over 20 seasons of field work there and explains how extreme fractionation of the magma might be responsible for the one-of-a-kind central complexes. Brian Upton is Emeritus Professor of Geology at the University of Edinburgh. During his long and prolific research career, he has conducted field studies in many parts of the world, concentrating especially on the Arctic. But throughout his career he has continued to investigate the unique alkaline rocks of South Greenland. As he explains in the podcast, these rocks contain an unrivalled number of exotic minerals, many of them not known to occur anywhere else. Web: geologybites.com Twitter: @geology_bites Insta: geologybites email: geologybitespodcast@gmail.com

Subduction zones are places where a slab of oceanic lithosphere plunges down into the mantle below. The slab consists of the sediments on top, crustal rocks in the middle, and the lithospheric mantle on the bottom, all plunging down together as a kind of sandwich. In each of these layers is an ingredient that plays a key role in shaping the evolution of the Earth over geological time – and that is water. Geoff Abers has conducted extensive research on water in subduction zones. In this episode, he explains how he uses seismic observations to map the distribution of water in subducting plates and in the overriding mantle. He then couples these observations with computer-based models of the physics and chemistry of the subducting plates to predict the fate of the water in the downgoing plate. The results are surprising — over geological time the amount of water in all of today's oceans may have been mixed into the deep mantle by subducting plates. Geoff Abers is Professor of Geological Sciences at Cornell University.

Popular reconstructions of ancient environments, whether they be in natural history museum dioramas, in movies, or in books, present a world of color. But are those colors just fanciful renderings, perhaps based on the colors we see around us today? Or is there evidence in the fossil record that we can use to determine the actual color of plants and animals that lived in the geological past? Maria McNamara tries to answer these questions by studying the fossil preservation of soft tissues, such as skin, muscle, and internal organs. She does this by analyzing fossils that come from sedimentary deposits that contain extraordinarily well-preserved fossils. She also does lab experiments to investigate the processes of soft tissue degradation and preservation. She is Professor of Paleontology at University College Cork in Ireland. For illustrations supporting this podcast, go to geologybites.com.

For many years, efforts to limit climate change have focused on curtailing anthropogenic emissions of greenhouse gases. But it is increasingly clear that such curtailment will not, on its own, be able to prevent the damaging effects of global warming. Therefore, more attention is now directed to mitigating climate change by enhancing the removal or sequestration of greenhouse gases from the atmosphere. As a result, our climate change goals are now often specified in terms of when we plan to reach net zero emissions rather than on when we can just reach emission reduction targets. Phil Renforth is an expert on carbon sequestration. He is especially interested in enhancing the weathering of rocks and has performed in-depth investigations of geochemical techniques of removing atmospheric carbon dioxide. He is an Associate Professor in the School of Engineering and Physical Sciences at Herriot-Watt University. There are illustrations supporting this episode at geologybites.com.

When plate tectonics was adopted in the 1960s and early '70s, researchers quickly mapped out plate movements. It seemed that plates moved as rigid caps about a pole on the Earth's surface. But since then, a lot of evidence has accumulated suggesting that plates are not, in fact, totally rigid. In fact, we can see them flex in response to stresses that are imposed on them. Such stresses can arise on plate boundaries, such as when two plates collide and one plate flexes down to subduct under the other. For example, we see a flexural bulge in Northern India where the Indian plate bends down under the Eurasian plate. Similar bulges are seen at subduction zones where the oceanic lithosphere flexes up before it bends down into a trench, such as off the eastern coast of Japan. Stresses can also be imposed in plate interiors when the plate is subjected to a load, such as a volcano or a sedimentary basin. An example of sediment loading occurs in river deltas, such as that of the Ganges in the Bay of Bengal. Our guest today pioneered an ingenious method of determining the flexural strength of oceanic plates. The method uses the flexural sag of plates in response to the weight of seamounts, most of which were emplaced on their surfaces by mid-ocean eruptions. His results suggest that less than half of an oceanic plate actually contributes to its elastic strength. The rest is brittle (top layer) or ductile on the relevant time scales (bottom layer).Tony Watts is Professor of Marine Geology and Geophysics at the University of Oxford and a Fellow of the Royal Society. If you like Geology Bites, please rate and review the podcast. It helps others find it.

Life only emerged from water in the Ordovician. By that time, life had been thriving in oceans and lakes for billions of years. What did the colonization of the land look like, and how did it reshape the Earth's surface? Neil Davies describes how we can decipher the stratigraphic sedimentary record to address these questions. Perhaps surprisingly, it's easier to recognize small and fleeting events than to recognize large-scale features such as mountains, valleys, and floodplains. He also describes his remarkable 2018 discovery of the largest known arthropod in Earth history — a 2.6-meter-long millipede. Neil Davies is a Lecturer in Sedimentary Geology at the University of Cambridge. He studies the interconnections and feedback loops between life and sedimentation. His research aims to understand how such interactions manifest themselves in the rock record. He does this by combining analyses of sedimentary structures and textures, stratigraphy, and trace fossils.

The asteroid Psyche is probably the most metal-rich body we have discovered. There are two, quite different, theories as to how it may have formed: Either it formed that way, or it originally had a more typical composition, but its rocky outer portion was blasted off during a major collision. To help determine which is most likely, NASA is sending a space probe there, to be launched on August 1, 2022. And if we can unravel the history of Psyche, we will also learn how other planets may have formed, since both the asteroids and the planets are thought to have been assembled from the same population of planetesimals – the small bodies that first formed out of the solar nebula. We might also learn about the Earth's own metallic core, since, according to the second theory, Psyche may be a naked core. Ben Weiss is Deputy Principal Investigator and Magnetometry Investigation Lead on the Psyche mission. He is a Professor of Planetary Sciences at the Massachusetts Institute of Technology. His research focuses on the formation, evolution, and history of the terrestrial planets and small bodies. He is especially interested in paleomagnetism and geomagnetism. In the podcast, he explains the various formation scenarios for Psyche. He then describes the various instruments on board the spacecraft and what we will be able to infer from the measurements they will make when orbiting the asteroid.

We hear about earthquakes in the Himalaya, especially when they claim lives and cause damage. And we understand that, broadly speaking, it is the continued northward movement of India ploughing into Tibet that causes these earthquakes. But where exactly do the earthquakes occur, how do they occur, and what determines how much damage they inflict? Roger Bilham has conducted a detailed study of the historical record of earthquakes in the Himalaya over the past millennium. He tries to reconcile what we've observed with our current understanding of the physical mechanisms at play. This in turn helps us assess future hazard potential. He is Emeritus Professor of Geology at the University of Colorado, Boulder. For podcast illustrations and more about Geology Bites, go to geologybites.com.

The fossil record of complex life goes back far beyond the Cambrian explosion, to as far back as 1,600 million years ago in the late Paleoproterozoic with the first appearance of eukaryotes. But these creatures only started to diversify much later, around 750 million years ago. What enabled this evolutionary change has been a puzzle, but one idea is that it reflects the appearance of microscopic predators. In the podcast, Susannah Porter tells us how she discovered incontrovertible signs of predation in vase-shaped microfossils dating from this period. Susannah Porter is a professor in the Department of Earth Sciences at the University of California, Santa Barbara. She studies microfossils of eukaryotic life forms that lived in the Neoproterozoic, about 750 million years ago. Website: geologybites.com with illustrations supporting each podcast Instagram: @oliverstrimpel Twitter: @geology_bites Email: geologybitespodcast@gmail.com