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?

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

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.