EF3C. Stay Current—What Heats the Earth’s Interior?
Staying current for Chapter 3
California Earthquake animation site at USGS
2023-02-23. What’s Inside Earth’s Inner Core? Seismic Waves Reveal an Innermost Core. [https://www.nytimes.com/2023/02/23/science/earth-core-seismic-waves.html] By Kenneth Chang, The New York Times. Excerpt: Geology textbooks almost inevitably include a cutaway diagram of the Earth showing four neatly delineated layers: a thin outer shell of rock that we live on known as the crust; the mantle, where rocks flow like an extremely viscous liquid, driving the movement of continents and the lifting of mountains; a liquid outer core of iron and nickel that generates the planet’s magnetic field; and a solid inner core. Analyzing the crisscrossing of seismic waves from large earthquakes, two Australian scientists say there is a distinctly different layer at the very center of the Earth. “We have now confirmed the existence of the innermost inner core,” said one of the scientists, Hrvoje Tkalcić, a professor of geophysics at the Australian National University in Canberra. Dr. Tkalcic and Thanh-Son Pham …estimate that the innermost inner core is about 800 miles wide; the entire inner core is about 1,500 miles wide. Their findings were published on Tuesday in the journal Nature Communications. While the cutaway diagram appears to depict clear-cut divisions, knowledge about the deep interior of Earth is unavoidably fuzzy. …Most of what is known about what lies beneath comes from seismic waves — the vibrations of earthquakes traveling through and around the planet. Think of them as a giant sonogram of Earth….
2023-01-23. Earth’s Inner Core: A Shifting, Spinning Mystery’s Latest Twist. [https://www.nytimes.com/2023/01/23/science/earth-core-reversing-spin.html] By Robin George Andrews, The New York Times. Excerpt: Imagine Earth’s inner core — the dense center of our planet — as a heavy, metal ballerina. This iron-rich dancer is capable of pirouetting at ever-changing speeds. …Seismologists reported Monday in the journal Nature Geoscience that after brief but peculiar pauses, the inner core changes how it spins — relative to the motion of Earth’s surface — perhaps once every few decades. And, right now, one such reversal may be underway. …fret not: Precisely nothing apocalyptic will result from this planetary spin cycle, which may have been happening for eons….
2022-03-31. The Planet Inside. By Paul Voosen, Science Magazine. Excerpt: Scientists are probing the secrets of the inner core—and learning how it might have saved life on Earth. …Earth’s magnetic field, nearly as old as the planet itself, protects life from damaging space radiation. But 565 million years ago, the field was sputtering, dropping to 10% of today’s strength, according to a recent discovery. Then, almost miraculously, over the course of just a few tens of millions of years, it regained its strength—just in time for the sudden profusion of complex multicellular life known as the Cambrian explosion. What could have caused the rapid revival? Increasingly, scientists believe it was the birth of Earth’s inner core, a sphere of solid iron that sits within the molten outer core, where churning metal generates the planet’s magnetic field. Once the inner core was born, possibly 4 billion years after the planet itself, its treelike growth—accreting a few millimeters per year at its surface—would have turbocharged motions in the outer core, reviving the faltering magnetic field and renewing the protective shield for life.… [https://www.science.org/content/article/scientists-probing-secrets-earths-inner-core-saved-life-planet]
2021-11-05. A Simple Recipe for Making the First Continental Crust. By Anastassia Y. Borisova and Anne Nédélec, Eos/AGU. Excerpt: Laboratory experiments serendipitously revealed a rock-forming process that might explain how the first continental crust formed on Earth—and possibly on Mars.… [https://eos.org/science-updates/a-simple-recipe-for-making-the-first-continental-crust]
2021-03-25. Cratons, Why Are You Still Here? By Jyotirmoy Paul, Eos/AGU. Excerpt: Most of the rock we see around us, from the ocean floor to the tallest mountains of the Himalayas, is no more than a few hundred million years old. The oldest oceanic rock is about 230 million years old, for example, and little continental rock is more than a couple of billion years old [Poupinet and Shapiro, 2009]. …None of the rock on Earth’s surface dates back to the planet’s earliest days, but detailed studies of isotopic decay in minerals from Earth’s mantle and from meteorites and lunar samples have produced a consensus that the planet is 4.54 billion years old, give or take 50 million years, at least. …Plate tectonics, coupled with convection in the mantle, governs the destructive forces applied to Earth’s lithosphere, its topmost layer of rock. Whereas oceanic lithosphere is recycled in subduction zones after a couple of hundred million years or so, continental lithosphere often survives longer but is still ultimately deformed, eroded, and destroyed by forces exerted by the underlying convective mantle. Thus, on a tectonically active Earth, rocks older than a few billion years should be rare to nearly nonexistent. However, such ancient rock, dating back more than 3 billion years (and perhaps even more than 4 billion years), has been found in different parts of the world (Figure 1). These very old rocks are known as cratons, from the Greek root word κράτος, meaning strength. Understanding how cratons have survived for such a long time, some almost since the birth of the planet, remains one of the grand challenges of geodynamics…. [https://eos.org/features/cratons-why-are-you-still-here]
2020-12-15. New Volcano, Old Caldera. By Alka Tripathy-Lang, Eos/AGU. Excerpt: Researchers suggest a magma chamber sits within an old submarine caldera structure that extends into the mantle. …In May of 2018, a barrage of earthquakes struck Mayotte, the seismically quiet easternmost island of the Comoros archipelago, which stretches between Africa and Madagascar. After months of investigating the unexpected, intense seismic activity, French scientists discovered a new submarine volcano in the Indian Ocean approximately 50 kilometers east of the island. This new seafloor feature is, by volume, the largest documented underwater volcanic eruption in history, and both volcanic and seismic activities continue today. …marine geologist Nathalie Feuillet and seismo-tectonicist Eric Jacques, both at the Institut de Physique du Globe de Paris, and their colleagues proposed the presence of a large underwater caldera—a volcanic depression formed when a magma chamber drains and collapses—located between Mayotte and the new volcano. A ring of earthquakes in the mantle lithosphere delineates this curious structure at depths where neither earthquakes nor calderas typically occur. …Earthquakes usually rupture brittle crust, where strain energy can accumulate, he said. Strain cannot accumulate at typical mantle conditions, so most mantle tends to flow, inhibiting the breaks of earthquakes. “One way to [get mantle earthquakes] would be to bring down cooler materials that can host earthquakes,” Fan said, which happens in subduction zones. But the Mayotte events are not related to subduction, leaving these mantle earthquakes a mystery…. [https://eos.org/articles/new-volcano-old-caldera]
2020-02-20. The Future of the Carbon Cycle in a Changing Climate. By By Aleya Kaushik, Jake Graham, Kalyn Dorheim, Ryan Kramer, Jonathan Wang, and Brendan Byrne, Eos/AGU. Excerpt: Over the past 50 years, a growing wealth of long-term atmosphere, ocean, and ecosystem observations has provided essential insights into how climate change affects the ways that carbon moves through Earth’s environment, yet many fundamental questions remain unanswered. Perhaps the most challenging and societally relevant question is whether the rate at which the land and ocean can sequester carbon will continue to keep pace with rising carbon dioxide emissions. Emissions of carbon dioxide (CO2) and methane (CH4) stemming from human activities are rapidly and dramatically altering Earth’s climate. Warmer temperatures drive longer and more destructive fire seasons, shifting precipitation patterns cause flooding in some areas and drought in others, and ocean acidification threatens marine life across the globe. However, land and ocean ecosystems act as natural buffers that limit the increase of CO2 in the atmosphere by absorbing and sequestering nearly half of emitted CO2. Although anthropogenic greenhouse gas emissions continue to increase, this natural climate change mitigation has so far proportionally kept pace with emissions, limiting global warming to a certain extent (Figure 1). This situation could change, however. For example, although tropical forests in the Amazon have been CO2 sinks over the past 50 years, increasing land use change, drought, fires, and tree deaths in recent years may have tipped the balance, making this region a periodic net carbon source…. [https://eos.org/features/the-future-of-the-carbon-cycle-in-a-changing-climate] ________________________
2019-02-27. The Unsolved Mystery of the Earth Blobs. By Jenessa Duncombe, Eos/AGU. Excerpt: Researchers peering into Earth’s interior found two continent-sized structures that upend our picture of the mantle. What could their existence mean for us back on Earth’s surface? Some 2,000 kilometers beneath our feet, there are enormous masses of hot mantle material that have baffled scientists for the last 4 decades. The blobs, as some scientists have taken to calling them, are the length of continents and stretch 100 times higher than Mount Everest. They sit at the bottom of Earth’s rocky mantle above the molten outer core, a place so deep that Earth’s elements are squeezed beyond recognition. The blobs are made of rock, just like the rest of the mantle, but they may be hotter and heavier and hold a key to unlocking the story of Earth’s past. Scientists first spotted the blobs in the late 1970s. Researchers had just invented a new way to peer inside Earth: seismic tomography. When an earthquake shakes the planet, it lets out waves of energy in all directions. …The process is similar to a doctor using an ultrasound device to image a fetus in the womb. …Earth is the only planet known to contain plate tectonics, and recent research has suggested that tectonics may help sustain life by delivering a steady stream of nutrients, like nitrogen and phosphorus, to the surface. And yet researchers aren’t sure what causes plate tectonic movement, let alone the blobs….
2017-05-01. Understanding Kamchatka’s Extraordinary Volcano Cluster.By Nikolai M. Shapiro et al, Earth & Space News EoS (AGU). xcerpt: Soaring 4750 meters above the Kamchatka Peninsula near the western shore of the Bering Sea, the Klyuchevskoy volcano is one of the most active in the world. …in 2015–2016, … an international collaboration conducted the first geophysical survey of the entire KVG. The effort was named the Klyuchevskoy Investigation—Seismic Structure of an Extraordinary Volcanic System (KISS) experiment. Data from KISS’s instrument network offer an unprecedented look at one of Earth’s most active volcanic regions and could reveal whether the underlying magma reservoirs are connected by one large volcanic supercomplex. ..Because of its strong and variable activity, the KVG is a unique natural laboratory for studying volcanism in a subduction zone. …Volcanic eruptions regularly affect a few small settlements located near the KVG, and they pose a significant threat to aviation because many international flights that connect North America and Asia pass over Kamchatka. Large explosive eruptions such as those of Bezymianny in 1956 and Shiveluch in 1964, when about 1 cubic kilometer of erupted material was ejected, might be particularly dangerous…. https://eos.org/project-updates/understanding-kamchatkas-extraordinary-volcano-cluster
2017-04-05. Balloons of Lava Bubble into the Ocean from Seafloor Blisters. By Lauren Lipuma, Earth & Space News, AGU. Excerpt: These peculiar features of submarine volcanic eruptions could be the result of undersea lava lakes. Imagine that you’re a fisherman at sea and suddenly your boat is surrounded by dozens of floating pieces of hot, dark rock, hissing and spewing vapor. Some rocks are no bigger than footballs, and some are larger than refrigerators. But just a few minutes later, the mysterious chunks sink below the surface without any hint of where they came from. That is exactly what happened to a group of fishermen in the Azores, Portugal, in late 1998. It turns out they were witnessing the appearance of lava balloons: floating lumps of hollow, cooled lava burped up from the seafloor after an undersea volcanic eruption. The fishermen described the balloons as “hot steaming stones whose high temperature caused minor damage to the fishing ropes,” with “fire coming out from the seawater spreading on the air like sparks of fireworks,”…. The balloons are a strange and rare phenomenon, but they also serve a scientific purpose: They alert researchers to underwater eruptions that might otherwise go unnoticed, said Ulrich Küppers, a volcanologist at the University of Munich. …He suspects they are the result of trapped magmatic gas pushing upward through lava during some kinds of undersea eruptions. Küppers presented his theory at the recent AGU Chapman Conference on submarine volcanism in Hobart, Tasmania…. https://eos.org/articles/balloons-of-lava-bubble-into-the-ocean-from-seafloor-blisters
2016-09-06. Scientists may have solved mystery of giant Midwest earthquakes. By Elizabeth Deatrick, Science. Excerpt: Two centuries ago, a series of giant earthquakes rocked the tiny town of New Madrid, Missouri, collapsing chimneys and shaking houses more than 1000 kilometers away. It was even said that parts of the Mississippi River momentarily flowed backward as the riverbed heaved upward. …Even today, the New Madrid Seismic Zone (NMSZ) generates more than 200 small tremors each year—and now a team of geophysicists thinks it knows what causes all the shaking. …In a new study, they use tomographic information about Earth’s interior to show how blobs of dense rock from the lower crust rise up underneath the region. This dense rock gravitationally tugs on everything else around it, changing regional stresses in a way that makes some NMSZ faults more likely to slip. …“We’re interested in creating an honest-to-goodness map of where we think earthquakes will occur in the future,” says lead author Will Levandowski, a geophysicist with the United States Geological Survey (USGS) in Golden, Colorado. …Experts say the work could be used to explain why some areas are more prone to human-induced earthquakes, such as Oklahoma, which now sees more earthquakes than California. Fracking-related activities might be more likely to trigger an earthquake in an area that was already under stress, according to Roland Bürgmann, a geophysicist at the University of California, Berkeley…. http://www.sciencemag.org/news/2016/09/scientists-may-have-solved-mystery-giant-midwest-earthquakes
2014-10-14. Earth’s magnetic field could flip within a human lifetime. Excerpt: …Earth’s magnetic field has flipped – though not overnight – many times throughout the planet’s history. Its dipole magnetic field, like that of a bar magnet, remains about the same intensity for thousands to millions of years, but for incompletely known reasons it occasionally weakens and, presumably over a few thousand years, reverses direction. …Now, a new study by a team of scientists from Italy, France, Columbia University and the University of California, Berkeley, demonstrates that the last magnetic reversal 786,000 years ago actually happened very quickly, in less than 100 years – roughly a human lifetime. …Courtney Sprain… and Paul Renne, director of the Berkeley Geochronology Center and a UC Berkeley professor-in- residence of earth and planetary science, are coauthors of the study, which will be published in the November issue of Geophysical Journal International and is now available online. [http://gji.oxfordjournals.org/content/199/2/1110] …The discovery comes as new evidence indicates that the intensity of Earth’s magnetic field is decreasing 10 times faster than normal, leading some geophysicists to predict a reversal within a few thousand years. Though a magnetic reversal is a major planet-wide event driven by convection in Earth’s iron core, there are no documented catastrophes associated with past reversals, despite much searching in the geologic and biologic record. Today, however, such a reversal could potentially wreak havoc with our electrical grid, generating currents that might take it down. And since Earth’s magnetic field protects life from energetic particles from the sun and cosmic rays, both of which can cause genetic mutations, a weakening or temporary loss of the field before a permanent reversal could increase cancer rates…. By Robert Sanders, Media Relations UC BERKELEY. http://newscenter.berkeley.edu/2014/10/14/earths-magnetic-field-could-flip-within-a-human-lifetime/ *.
2014-06-16. The Earth’s Hidden Ocean. Excerpt: An analysis of seismic waves passing through the deep earth appears to confirm what laboratory experiments have suggested was possible: that an ocean of water is tied up in the mantle, 400 miles below the surface. Any voyager to the center of the earth could leave the wet suit behind, however. The water is not liquid, but rather bound in minerals that exist at the extreme pressures found at such depths. …“It’s a new view of the structure of this part of the earth,” said Brandon Schmandt, a geophysicist at the University of New Mexico and an author of a recent paper in the journal Science describing the research. The work also adds credence to the idea that the earth’s water accumulated in the interior during the planet’s formation, rather than arriving later through the bombardment of icy comets. In this view, water bound up in minerals in the mantle, the 1,800-mile-thick layer between the thin crust and the hot metallic core, degassed over time and reached the surface. The scientists studied a part of the mantle called the transition zone, from about 300 to 440 miles deep. The ability of this zone to contain water — and apparently to retain a lot of it — “may have something to do with stabilizing or buffering the size of the oceans,” said Steven D. Jacobsen, a mineralogist at Northwestern University and another author of the paper. “It may be fortunate that the earth’s interior can act like a sponge.” …it’s not as if there are huge chambers of magma hundreds of miles below the surface, Dr. Jacobsen said. The melting occurs on the boundaries of the mineral grains. “You end up having a mushy rock,” he said. http://www.nytimes.com/2014/06/17/science/the-earths-hidden-ocean.html. By Henry Fountain.
2012 May 28. Earth’s Core – The Enigma 1,800 Miles Below Us. By Natalie Angier, The NY Times. Excerpt: Geologists have long known that Earth’s core, some 1,800 miles beneath our feet, is a dense, chemically doped ball of iron roughly the size of Mars and every bit as alien… Researchers have also known that the core’s heat helps animate the giant jigsaw puzzle of tectonic plates floating far above it, to build up mountains and gouge out seabeds. At the same time, the jostling of core iron generates Earth’s magnetic field. Now it turns out that existing models of the core, for all their drama, may not be dramatic enough. Dario Alfè of University College London and his colleagues presented evidence that iron in the outer layers of the core is frittering away heat through the wasteful process called conduction at two to three times the rate of previous estimates. The theoretical consequences of this discrepancy are far-reaching. The scientists say something else must be going on in Earth’s depths to account for the missing thermal energy in their calculations….
2010 September. What’s Really Shaking. By Kathleen M. Wong, Science Matters @ Berkeley. Excerpt: …Many types of phenomena, from the shudders of a glacier to the detonation of a nuclear bomb, can move mountains and get entire regions rocking.
Berkeley professor of earth and planetary science Douglas Dreger analyzes the seismic signatures left behind by these and other exotic, earthquake-like events. His work is aiding fields as diverse as glaciology, mine rescues, and nuclear treaty enforcement.
Dreger takes full advantage of the data from modern digital broadband seismometers…. Dreger filters such digital seismograms to reveal far more than shaking magnitude. Using a technique called moment tensor inversion, he can distinguish true earthquakes from mine implosions, volcanic eruptions, and nuclear tests.
2010 May. Bobbing for Carbon. By Kathleen M. Wong. ScienceMatters, Berkeley. Excerpt: …Think your garden is green? The blue waters of the oceans are actually much greener. Every year, microscopic marine plants called phytoplankton convert roughly 50 petagrams—50 trillion kilograms—of carbon dissolved in ocean surface waters into living tissue. That’s half of all the photosynthesis that occurs on the planet, and it happens at an astoundingly rapid pace.
…To overcome these hurdles, Bishop has developed a fully autonomous phytoplankton sampling robot. Dubbed the Carbon Explorer, it is designed to rise to the surface and sink back down to 1,000 meters, sampling plankton and ocean conditions all the way. Bishop’s robots cost about $30,000 each, the equivalent of operating a research vessel for a single day, yet can continue gathering data twice a day in absence of ships for over a year. And they are tough. One operated in the ice surrounding Antarctica for an entire winter, transmitting data to shore weekly and emerging unscathed in spring.
2006 November 13. THE DARKENING SEA. By ELIZABETH KOLBERT, “The New Yorker” Issue of 2006-11-20. What carbon emissions are doing to the ocean. …In the nineteen-nineties, researchers … collected more than seventy thousand seawater samples … analysis of …which was completed in 2004, … nearly half of all the carbon dioxide that humans have emitted …has been absorbed by the sea. …carbonic acid …can change the water’s pH. Already, humans have pumped enough carbon into the oceans…to produce a .1 decline in surface pH. Since pH … is a logarithmic measure, a .1 drop represents a rise in acidity of about thirty per cent. The process is … “ocean acidification,” … term coined in 2003 by two climate scientists, Ken Caldeira and Michael Wickett, …at the Lawrence Livermore National Laboratory. …Caldeira …to brief some members of Congress… was asked, ‘What is the appropriate stabilization target for atmospheric CO2?’ ” … “And I said, ‘Well, I think it’s inappropriate to think in terms of stabilization targets. I think we should think in terms of emissions targets.’ And they said, ‘O.K., what’s the appropriate emissions target?’ And I said, ‘Zero.’ “If you’re talking about mugging little old ladies, you don’t say, ‘What’s our target for the rate of mugging little old ladies?’ You say, ‘Mugging little old ladies is bad, and we’re going to try to eliminate it.’ …Coral reefs are under threat…. When water temperatures rise too high, corals lose…the algae that nourish them. (The process is called “bleaching,” because without their zooxanthellae corals appear white.) …The seas have a built-in buffering capacity: if the water’s pH starts to drop, shells and shell fragments that have been deposited on the ocean floor begin to dissolve, pushing the pH back up again. This buffering mechanism is highly effective, provided that acidification takes place on the same timescale as deep-ocean circulation. (One complete exchange of surface and bottom water takes thousands of years.) …Currently, CO2 is being released into the air at least three times and perhaps as much as thirty times as quickly …so fast that buffering by ocean sediments is not even a factor….
2005 November 23. HOW DOES RADIOACTIVE DECAY WORK?, Teaching Quantitative Skills in the Geosciences, Jennifer M. Wenner, University of Wisconsin-Oshkosh, SERC, The concepts of spontaneous decay, isotopes, and half-lives are discussed as well as how geoscientists make use of radioactive decay in dating beds and deposits. This page is paired with another which tackles the mathematical issues behind exponential growth and decay equations to allow educators to teach both the abstract concept and the concrete example.
2005 February. The Virtual Physics Lab session is about the particle model of matter and looks at examples of the behavior of matter on a macroscopic level that are best explained by assuming matter was made of particles.
2005 February. USGS Animation of recent earthquakes worldwide
4 October 2004. EARTHQUAKE FORECAST PROGRAM HAS AMAZING SUCCESS RATE. NASA news. A NASA funded earthquake prediction program has an amazing track record. Published in 2002, the Rundle-Tiampo Forecast has accurately predicted the locations of 15 of California’s 16 largest earthquakes this decade, including last week’s tremors.
December 2003. A Mission to the Earth’s Core, by John G. Cramer. http://mist.npl.washington.edu:80/av/altvw120.html. Alternate View Column, published in Analog Science Fiction & Fact Magazine. Adventure stories involving the exploration of the interior of Planet Earth have a long and distinguished history in science fiction. Jules Verne’s Journey to the Center of the Earth (1864) was perhaps the first such tale. …Following Verne’s lead and doing considerably more violence to geology, paleontology, and physics, Edgar Rice Burroughs wrote seven novels beginning with At the Earth’s Core (1922) that were set in Pellucidar, a “land” occupying the inner surface of a vast spherical hole in the Earth’s hollow interior…. David Stevenson, a Professor of Planetary Science at CalTech, has proposed mounting an ambitious NASA-style mission to the Earth’s core. He describes his “modest proposal” (in the Swiftian sense) in a paper recently published in the journal Nature. … He proposes to use a multi-megaton nuclear weapon and one hour’s worth of the net iron production of the Earth’s iron smelter facilities (~10^8 kg). The annotated paper, A Modest Proposal: Mission to Earth’s Core, is at http://www.gps.caltech.edu/faculty/stevenson/coremission/