Editors’ Vox is a blog from AGU’s Publications Department.
The Earth’s deep interior is difficult to study directly but recent technological advances have enabled new observations, experiments, analysis, and simulations to better understand deep Earth processes. A new book in AGU’s Geophysical Monograph Series, Core-Mantle Co-Evolution: An Interdisciplinary Approach, provides the latest insights into dynamics, structure, and evolution in the core-mantle boundary region. We asked the lead editor to outline some exciting new developments in this field.
In simple terms, what are the main processes that happen in the Earth’s deep interior and why do they matter?
The cooling of liquid metal in the core generates rising and sinking motions that creates the Earth’s magnetic field. The magnetic field shields life at the Earth’s surface from the harmful effects of charged particles emitted by the Sun and bombarding the Earth from elsewhere in the galaxy.
Similar rising and sinking motion happens in the silicate mantle and this creates plate tectonics. Cooling of the planet overall moves the plates at the Earth’s surface and creates the geography of our planet – oceans, mountains, islands, the land we live on.
What is particularly interesting about interactions between the core and mantle?
At the core-mantle boundary [is] a chaotic marketplace of chemical exchange
There is hot, molten metal pressed against solid rock at the core-mantle boundary. The metal and rock are hot and chemically reactive. The metal wants to suck any metallic impurities in the rock into it, and conversely wants to get rid of any slag-like impurities it has. This creates a chaotic marketplace of chemical exchange.
With Earth’s deep interior impossible to study directly, what methods, techniques, and tools do scientists use to understand the processes taking place there?
We have a range of tools available to study the processes taking place in Earth’s deep interior. For example, in a laboratory, we can conduct high pressure experiments on rocks and metals to see how they behave in their crystal structure and material properties at the simulated condition of Earth’s deep interior. We can also collect recordings of earthquakes that travel through the deep Earth to understand more about the structure of the Earth’s interior. Another thing we can measure are changes in the Earth’s magnetic field, which visually show us the auroral oval in the clear night sky as a result of interaction between Earth’s magnetic field and solar activity. We can also use computer simulations to understand rock and metal properties, and to model whole-earth evolution.
What would you pick as one of the most exciting recent advances in our understanding of core-mantle interaction and co-evolution?
Through research across disciplines we now know about the dissolution of silicate which results in thermal and chemical interactions between the silicate mantle and metallic core. This might help to explain magnetic field generation in the evolution of the Earth.
How is an interdisciplinary approach helpful in studying core-mantle processes
We are able to discover so much more when scientists from different disciplines work together on a problem.
We are able to discover so much more when scientists from different disciplines work together on a problem. The contributors to our book come from many different fields which enables a more comprehensive understanding. For example, seismology can image the structure of the Earth’s deep interior, while high pressure experiments can identify material properties under temperature and pressure conditions at the core-mantle boundary. By combining the two approaches, we can build a picture of the dynamics of core-mantle processes. However, the fundamental physics and chemistry of those processes cannot be understood by those two approaches alone: computer simulations and thermodynamics theory can be used to quantify the key processes.
What are some of the gaps in our understanding and unresolved questions about core-mantle interactions and co-evolution?
Hydrogen is the most abundant element in the universe, but we don’t know very much about how it gets incorporated into the metal that makes up the core of the Earth. Better knowledge of the hydrogen-iron system will help us address questions such as what is the temperature at the core-mantle boundary. In ten years’ time, hydrogen’s effects will probably be much better understood.
Your book comes 25 years after AGU published The Core‐Mantle Boundary Region. What do you imagine will be the latest developments reported in another book 25 years from now?
In my opinion, how and where heat is generated inside the Earth by radioactive decay will be the major advance in 25 years’ time. The chapters in our book describing the new detection methods point to how we might start to answer this question.
Core-Mantle Co-Evolution: An Interdisciplinary Approach, 2023. ISBN: 978-1-119-52690-2. List price: $204.95 (hardcover), $164.00 (e-book)
Chapter 1 is freely available. Visit the book’s page on Wiley.com and click on “Read an Excerpt” below the cover image.
—Takashi Nakagawa (takashi.geodynamics@gmail.com; 
0000-0003-3179-6462), Kobe University and Hiroshima University, Japan; Taku Tsuchiya, Ehime University, Japan; Madhusoodhan Satish-Kumar, Niigata University, Japan; and George Helffrich, Tokyo Institute of Technology, Japan
Editor’s Note: It is the policy of AGU Publications to invite the authors or editors of newly published books to write a summary for Eos Editors’ Vox.