3. Earth's Interior

What Heats the Earth's Interior?

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.

2017-05-01. Understanding Kamchatka’s Extraordinary Volcano Cluster. By Nikolai M. Shapiro et al, Earth & Space News EoS (AGU). 

2017-04-05. Balloons of Lava Bubble into the Ocean from Seafloor Blisters. By Lauren Lipuma, Earth & Space News, AGU.

2016-09-06. Scientists may have solved mystery of giant Midwest earthquakes. By Elizabeth Deatrick, Science.

2014-10-14. Earth’s 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/

2003 to Present

California Earthquake animation site at USGS

Deep Carbon Observatory