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.