Geology Bites: An Earth and Planetary Science Podcast

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.

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.

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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.

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.

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