Episodes
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,...
Published 06/17/22
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...
Published 06/01/22
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...
Published 05/12/22
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...
Published 04/24/22
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...
Published 04/12/22
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...
Published 03/22/22
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...
Published 03/01/22
Does the pull of a subducting slab drive plate motions?  Or is it the upwellings of convection cells in the mantle?  We now have a new way to shed light on this question.  It's called seismic anisotropy, which is the spreading out of seismic waves according to their direction of polarization.  This happens when the mantle through which the waves travel has crystals which are preferentially aligned, and that occurs when there is deformation or flow going on.  So we can work backwards to use...
Published 02/21/22
There’s a lot of debate about the idea that the global changes brought about by humans define a new geological epoch, dubbed the Anthropocene. Should such an epoch be added to the official geological time scale? If so, what aspect or aspects of anthropogenic change should be used, and exactly where do we place the golden spike that will define the base of the Anthropocene? Such questions come under the purview of the International Commission on Stratigraphy, whose current secretary general...
Published 02/12/22
Subduction zones are a fundamental aspect of plate tectonics, yet we still don't really understand how subduction initiates.  It's a tough problem because as oceanic plates move away from a mid-ocean spreading center and cool, they get stiffer and should become more and more resistant to bending and sinking down into the mantle.  But recent work suggests that the clue to this puzzle lies in the physics of grains at the microscale.   David Bercovici is one of the geologists who has pioneered...
Published 02/05/22
New rock types emerge during the history of the Earth.  For example, the silica-rich felsic rocks such as granite that characterize continental crust, accumulated during the course of Earth history.  Granite only forms in certain specific tectonic settings, such as above subduction zones and when lower crustal rocks melt in mountain belts.  But what about the minerals themselves?  Have they been around since the Earth formed, or did they too only appear on the scene later as a result of some...
Published 01/25/22
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