Episodes
Matt Jackson is a Professor of Earth Science at the University of California, Santa Barbara.  He probes the chemical composition of the mantle by analyzing trace elements and isotopes in hot-spot lavas from around the world.  In the podcast, he describes the intriguing heterogeneity among the hot-spots of the so-called “hot-spot highway” in the western Pacific.  The heterogeneity there, as well as on larger spatial scales is challenging our ideas about the motions of the mantle over the...
Published 01/08/22
Throughout geological history, various points on the Earth’s surface have been lifted up to great elevations and worn down into low, flat-lying regions.  Determining surface elevation histories is difficult because rocks that were once on the surface are usually eroded away or buried.  Furthermore, most rock-forming processes are not directly affected by elevation.  But it turns out that we can overcome these challenges, as Carmie Garzione explains in the podcast.  Carmie Garzione is Dean of...
Published 01/01/22
The magnetic stripes frozen into the sea floor as it forms at mid-ocean ridges record the Earth’s magnetic field at the time of formation.  Reversals in the Earth’s magnetic field define the edges of these stripes, in effect time-stamping the sea floor position. Chuck DeMets is Emeritus Professor of Geoscience at the University of Wisconsin, Madison.  He studies the magnetic anomalies in seafloor rocks to reconstruct plate motions at a temporal resolution five times better than has been done...
Published 12/25/21
As the name implies, oceanic lithosphere underlies the oceans of the world.  Except when they are ophiolites, when oceanic lithosphere is thrust on top of a continental margin.  Are ophiolites a special kind of oceanic lithosphere?  Or are there peculiar tectonic circumstances that emplace denser oceanic rocks on top of lighter continental ones?  Mike Searle addresses these questions, and reveals the sequence of events that created the world's most extensive and best-preserved ophiolite - the...
Published 12/18/21
Some of the most extensive sandstone deposits in the world were deposited by wind.  How do such aeolian rocks differ from water or ice-deposited rocks?  And  what do they reveal about the environments in which they formed?  In the podcast she describes the dunes we see in the geological record on Earth, as well as on Mars and on a comet, and explains what we've learned from them. Mackenzie Day is an Assistant Professor in the Department of Earth, Planetary, & Space Sciences at the...
Published 12/11/21
The best maps we have of Venus were made by Magellan, a space probe that flew in the 1990s.  In the summer of 2021, NASA approved a new mapping mission that will produce radically improved maps of the topography, radar reflectivity, and gravity field, and the first ever global map of surface rock type.  Sue Smrekar, the mission Principal Investigator, explains why this will revolutionize our understanding of Venus and perhaps also throw light on the early history of Earth when processes...
Published 12/04/21
Almost all the evidence about the nascent solar system has been erased by processes accompanying the formation of the Sun and the bodies that formed out of the circumsolar disk about 4.6 billion years ago.  But some meteorites and the tiny dust grains contained within them have anomalous compositions that can only be understood by invoking a history going back to the giant molecular cloud progenitor of the solar system, and to the stars that ejected the material that formed the cloud.  Rick...
Published 11/28/21
After months of high earthquake activity, a fissure opened up near the southwestern tip of Iceland on March 19, 2021. Over a period of about seven months, several other fissures opened up, generating lava flows several kilometers long that filled several valleys and created a new 150-meter high mountain, a sort of mini-shield volcano. The eruption has been intensively studied by geologists because it is the first eruption of its kind in Iceland in living memory, and also because it’s...
Published 11/13/21
Long before radiometric dating appeared on the scene, the geological time scale was defined by the sedimentary record, and particularly by key fossils preserved within them.  Throughout the Cambrian, and to a lesser extent until the end-Permian extinction about 300 million years later, trilobite fossils served as some of the most useful of these key fossils.  Richard Fortey explains why.  Here he is holding a trilobite from the calymene genus. Richard Fortey is formerly head of arthropod...
Published 11/07/21
We’re all familiar with the idea of ice ages during which the polar ice caps advance to cover significant portions of their respective hemispheres, and then, after a period of tens to hundreds of thousands of years, retreat back to the polar regions.  But now we believe that twice during the Earth’s history, the ice advanced all the way to the equator, almost completely blanketing the Earth with a sheet of ice several kilometers thick.  This is the Snowball Earth hypothesis.  In the podcast...
Published 11/01/21
The heat liberated during the formation of our planet created an ocean of magma.  As it began to cool, the Earth differentiated into a dense metallic core surrounded by a less dense rocky mantle.  At some point, we know that the surface of the Earth must have formed itself into the rigid blocks we call plates, and that these plates began to move and interact with each other as parts of the global process we call plate tectonics.  But did the plates form and did plate tectonics start soon...
Published 10/23/21
Many processes in geology affect the temperature of rocks.  Erosion is one example — as a surface is eroded, the rocks below get closer to the surface, cooling as they go.  So if we know the temperature history of a rock, we can infer its erosion history.  Becky Flowers has a thermochronology lab in which she determines the cooling history of rocks as recorded in specific crystals they contain, such as zircon and apatite.  She explains how this works, and how she has used her results to...
Published 10/16/21
The geological history of Central Europe is quite complicated.  The region is composed of several continental blocks having quite distinct origins that came together over 300 million years ago in the Paleozoic Era.  Then, in the Mesozoic, many of the original rocks were overlaid, and continued plate movements caused mountain belts to form.  In a previous Geology Bites podcast, Douwe van Hinsbergen explained how he used an analysis of the geological structure of mountain belts to reconstruct...
Published 10/09/21
Ever since Alfred Wegener proposed the theory of continental drift in 1912, we have been aware that blocks of the Earth’s lithosphere are moving with respect to each other.  With the advent of plate tectonics in the 1960s, these moving blocks became identified with the tectonic plates that tile the Earth’s surface.  We now have accurate measurements of plate motion speeds, which range from about ½ a cm per year to 10 cm per year.  But there is still no general consensus as to what makes...
Published 09/18/21
Oceanic plates are continually manufactured at mid-ocean spreading ridges.  But exactly what processes go on at these ridges?  It turns out that it depends on what type of ridge it is - fast-spreading or slow-spreading.  And that our traditional view of vanishingly thin plate thickness at ridge axes is inaccurate.  Mathilde Cannat describes our modern understanding of mid-ocean ridges and the observations that led us there. Mathilde Cannat is a research director at the Institut de Physique...
Published 08/19/21
The lithium-ion battery was invented about 40 years ago, and is now commonplace in a range of products, from smartphones to electric cars. But if we are to meet the carbon emission goals that governments are setting, electrification, and with it the need for electricity storage, will increase dramatically. Although many new electricity storage methods are being developed, none are as mature as the lithium-ion battery, which will therefore need to be a major part of a carbon-free...
Published 08/09/21
The fossil record goes back through the Phanerozoic eon, about 540 million years, and even earlier, into the Ediacaran period.  But while the fossils provide incontrovertible evidence of ancient life, the fossils themselves are certainly not alive.  In fossils, the original organic matter belonging to the fossilized life form has been replaced by inorganic materials, cast into the shape formerly occupied by the life form.  However, in some situations, the original organic matter does survive....
Published 07/28/21
The subfield of geology called geodynamics most commonly refers to the motions associated with convection in the mantle.   These are slow by human standards and lead to phenomena such as plate motions, seafloor spreading, mountain building, and volcanos.  But the Earth’s interior actually undergoes motion on a whole range of timescales.  The shortest of these occurs within seismic waves – in which the vibrations triggered by earthquakes cause tiny elastic movements of the material as they...
Published 06/12/21
Many hundreds of films have been shot on location in the American West.  The rugged, inhospitable landscapes are an integral part of what gives so many American Westerns their distinctive character.  Although the region is vast, stretching from the Rockies in Wyoming and Colorado to Utah, New Mexico, Nevada, Arizona and California, a few locations have captured the lion’s share of the film industry’s attention.  What is it about these landscapes that makes them so photogenic?  And how did...
Published 06/03/21
We know the Earth was born as a baking inferno. So the presence of a relatively cool surface today suggests that the Earth has cooled a lot since it formed. But the very thin crust on which we subsist is not representative of the Earth as a whole, and although some heat must be escaping from the Earth, there are also ongoing sources of heat. So the answer to the question as to whether Earth is cooling down is not straightforward. Claude Jaupart is Professor of Geophysics at the Université de...
Published 05/26/21
How can we tell what is happening at the bottom of the lithosphere, especially in one of the most remote places on the planet?  Peter Molnar describes how many diverse lines of evidence, from the fossil record to normal faulting point to abrupt elevation changes in Tibet, both before and well after India collided with it.  He thinks this tells us that the bottom of the thickened lithosphere there is gravitationally unstable and hot enough to literally drip off into the asthenosphere below,...
Published 05/13/21
Katie Stack is Deputy Project Scientist for the NASA Perseverance rover that landed in Jezero crater on Mars in February 2021.  A geologist by training and an expert on the Martian sedimentary rock record, she has been mapping the geology of Mars since the 2000s.  She leads a large team of scientists that will combine orbiter and rover image data to investigate processes that took place on the the ancient surface of Mars. She describes what we are learning with the powerful instruments...
Published 05/08/21
Jan Smit is a paleontologist who specializes in abrupt changes in the geological record.  After the discovery of an end-Cretaceous surge deposit in North Dakota, he was part of the team that pieced together the striking evidence it contained, particularly its perfectly preserved fossils and tiny glass spherules called tektites.  He describes how this led to a detailed picture of the dramatic events that unfolded within an hour or two following the asteroid impact. Jan Smit is Emeritus...
Published 05/03/21
Marie Edmonds is Professor of Volcanology and Petrology at Cambridge University.  She studies the cycling of volatile elements such as carbon between the atmosphere and the mantle and the role that volatiles play in melting, magma transport, and the style of  volcanic eruptions. She describes how all volcanos emit gas and how the gas can reveal a lot about the origin of the magma and also forewarn of eruptions.  Here is is monitoring gases emitted during the 2018 eruption of Kilauea on...
Published 04/30/21