Geology Bites: An Earth and Planetary Science Podcast

Latest Episodes:

Mackenzie Day on Dunes Dec 11, 2021

Show notes

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 University of California Los Angeles. She is an expert in aeolian processes. 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 how they formed.

Go to geologybites.com for podcast illustrations and to learn more about the series.

Sue Smrekar on the VERITAS Mission to Venus Dec 04, 2021

Show notes

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 analogous to those happening on Venus today may have occurred.

Sue Smrekar is a geophysicist who has played key scientific and managerial roles in multiple planetary exploration missions, include Magellan and the InSight robot lander on Mars.

Rick Carlson on Probing the Early Solar System Nov 28, 2021

Show notes

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 Carlson explains what the anomalies are and how we can use them to learn about what might have being going on in the solar nebular as the solar system was forming.

Rick Carlson is an isotope geochemist who measures such anomalies and uses them as clues to the birth of the solar system. He is Director of the Earth and Planets Lab at Carnegie Science in Washington DC.

Go to geologybites.com for podcast illustrations and to learn more about Geology Bites.

Ed Marshall on Iceland's 2021 Eruption Nov 13, 2021

Show notes

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 extremely accessible – just a short drive from Reykjavik.

Ed Marshall has made dozens of visits to the eruption site to sample the lava. He then performs geochemical analyses in his lab which show that the magma originates from the very bottom of the crust where it meets the convecting mantle. Such eruptions generally only occur at mid-ocean ridges, so this is a rare opportunity to study what is happening on the crust-mantle boundary. It appears to be a place where heterogenous batches of mantle are mixing vigorously, injecting rapidly changing melts into the conduit carrying the magma to the surface.

Ed Marshall is a Postdoctoral Research Fellow at the University of Iceland.

Richard Fortey on the Trilobite Chronometer Nov 07, 2021

Show notes

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 paleontology at the Natural History Museum in London and is visiting professor of paleobiology at Oxford University. He has devoted much of his research career to the study of trilobites — their systematics, evolution, and modes of life, and has named numerous trilobite species.

Podcast illustrations and more about Geology Bites are on geologbites.com.

Paul Hoffman on the Snowball Earth Hypothesis Nov 01, 2021

Show notes

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 Paul Hoffman explains the mechanisms that could have brought about a snowball Earth, and describes the extensive evidence that has now been amassed in support of two such periods in the Neoproterozoic, about 720 and 650 million years ago.

Paul Hoffman is Emeritus Professor of Geology at Harvard University. His research on the sedimentary rocks of Namibia, and that of his students in North America, Arctic Europe, and Mongolia, uncovered compelling evidence of glaciation near the equator about 650 million years ago in the Neoproterozoic. More than anyone else, he is responsible for synthesizing the evidence in the geological record to develop a persuasive case for a Snowball Earth.

For illustrations that support this podcast and to learn more about Geology Bites, go to geologybites.com.

Peter Cawood on When Plate Tectonics Started Oct 23, 2021

Show notes

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 after the Earth differentiated into the metallic core and rocky mantle over four billion years ago, or was there a long interim period before the initiation of plate tectonics? There is an ongoing debate about this, with some finding evidence for plate tectonics as far back as the Hadean, i.e., over 4 billion years ago, and others suggesting that it was not until the Neoproterozoic, about 750 million years ago, that modern plate tectonics got going.

Peter Cawood is a professor in the School of Earth, Atmosphere, and Environment at Monash University in Melbourne. His research aims to discover the origin of the Earth’s continents by studying the ancient interiors of continents called cratons. It is these cratons that preserve the clues as to the conditions and processes that prevailed in the early Earth, which in turn can tell us when and how plate tectonics started.

Becky Flowers on Deciphering the Thermal History of Rocks Oct 16, 2021

Show notes

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 unravel histories such as that of the Grand Canyon, the South African plateau, and even of that of the lunar surface.

Becky Flowers is a Professor of Geological Sciences at the University of Colorado, Boulder. She has a thermochronology lab in which she measures the amounts of the different radioactive decay products within crystals to figure out the cooling history of rocks. Knowing how rocks cooled gives us new insights on geological histories and processes of many parts of the Earth, and even of the Moon.

For podcast illustrations, and to learn more about Geology Bites, go to geologybites.com.

Ulf Linnemann on the Assembly of Central Europe in the Paleozoic Oct 09, 2021

Show notes

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 tectonic plate motions. In this episode, we hear about a totally different approach to reconstructing plate motions and paleogeography, and see how it was able to reveal the plate motions that assembled central Europe.

Ulf Linnemann is the Head of the Geochronology Department at the Senckenberg Museum of Mineralogy and Geology in Dresden. In his research he uses detrital zircon crystals, which are crystals that have survived the erosion of the magmatic rocks in which they formed, and that have been recycled into sedimentary rocks. His team has determined the ages of large populations of detrital zircons as the basis for disentangling the events that led to the assembly of central Europe.

Douwe van Hinsbergen on What Drives the Motions of Tectonic Plates Sep 18, 2021

Show notes

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 plates move. Broadly speaking, there are two competing explanations. In the first, the plates ride on top of convection cells of a vigorously convecting mantle. In the second, it is the forces acting on plate boundaries, principally the pull of dense lithospheric slabs subducting into a less dense mantle that drive the plates.

Douwe van Hinsbergen is a Professor of Global Tectonics and Paleogeography at the University of Utrecht. He has reconstructed the history of plate motions in various locations around the world with the primary goal of using this history to understand the dynamics of the mantle. And his latest research is directed to shedding light on the long-standing question as to what drives tectonic plates.

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