Geology Bites

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 thes...

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 the...

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...

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 pro...

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...

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....

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 w...

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 t...

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 t...

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...

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 fr...

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 observ...

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...

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...

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 seis...

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 fi...

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 coo...

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 lithosph...

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...

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 dram...

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 als...

Gillian Foulger is a leading proponent of the plate hypothesis of volcanism, which posits that volcanism away from plate boundaries can be explained by extensional deformation of the lithosphere with melting of the upper mantle.  The plate hypothesis uses plate tectonic theory to explain all volcanism without invoking plumes or hot-spots that originate in the lower mantle.  She hosts a l...

Sarah Stewart uses computer-based dynamical simulations and lab experiments to create scenarios for the collision of a massive body with the Earth that can reproduce the composition, orbits, and spins of the Earth and Moon today.   Sarah Stewart is a Professor in the Department of Earth and Planetary Sciences at the University of California Davis.  In the podcast, she explains how, follo...

Dietmar Müller and his team have built interactive software to combine hundreds of diverse geological research studies into a single self-consistent picture of the plate-tectonic motions over deep time.  He explains how this astonishing feat was accomplished and points out salient features in the results. Dietmar Müller is Professor of Geophysics at the University of Sydney.   In Fe...

Bob Anderson is chair of the department of Geological Sciences at the University of Colorado Boulder.  He is a geomorphologist who has studied many diverse aspects of the landscape, focusing recently on Alpine and Arctic landscapes in which ice plays a prominent role.  It was his sense of awe and aesthetic appreciation of patterns in nature that drew him into the field. In the podcast he...