Letter from the Directors | March 2020 | What's in a Name?

The geochemistry lab at the Earth and Planets Laboratory.
Thursday, March 05, 2020 


What’s in a Name?

Laboratory – noun - a place providing the opportunity for experimentation, observation, or practice in a field of study (Merriam-Webster)

At the Earth & Planets Laboratory, some of our work would fit anyone’s classical definition of laboratory, like the clean rooms that we use to dissolve rocks and minerals in preparation for isotopic analysis in our mass spectrometers and the multitude of laboratories on campus chock full of high-pressure apparatus and wide-ranging tools to interrogate samples at extremely small spatial scales, often while they are still under extreme conditions. 

Other aspects of our work fit the broader definition quoted above. For the theorists on campus, their laboratory is the computer and the programs they develop to explore questions from the processes of planet formation around stars to the dynamics of planetary interiors, to calculating the ways that atoms can interact to form new compounds. 

Another contingent on campus defines their laboratories as the natural world. These scientists collect rock samples from around the world (and outer space), use telescopes to peer into distant planetary systems, and deploy strategic arrays of instruments to look into Earth and the processes going on beneath our feet.

Experimental Lab: New Measurements Constrain Core Cooling

The why and when of Earth’s magnetic field, which arguably makes our planet habitable, depends critically on how quickly heat flows out of Earth’s liquid iron outer core. At the boundary between the core and the mantle, the key thing to know is the thermal conductivity of the silicate minerals in contact with the core—not an easy task given that measurements need to be made at about 1.3 million atmospheres pressure and 4000 degrees C! A pair of papers out this month exemplify how our modern high-pressure laboratory approaches shed new light on this long-standing and tremendously challenging problem.

There are two components to the thermal conductivity that need to be measured, the lattice component (think vibrating atoms) and the radiative component (think transparency). EPL staff scientists Alex Goncharov and research scientist Zack Geballe, together with former Carnegie postdoc Sergey Lobanov, have pioneered fast time-resolved spectroscopic and laser heating techniques to measure the thermal conductivity of deep mantle minerals at the extreme conditions of the core-mantle boundary. In a paper led by Geballe and Goncharov, and also including postdoc Nate Sime, staff scientist Peter van Keken, and former postdoc James Badro, the lattice conductivity is measured. In another paper led by Lobanov and a bevy of current and former Carnegie colleagues including Goncharov, radiative component is measured.

Part of the complex array of lasers, mirrors, and high-pressure tools that Zach Geballe and Alex Goncharov used to measure lattice conductivity.

Overall the results are consistent with a moderate rate of core cooling that implies a relatively young inner core age of about 1 billion years and both a thermally-and compositionally-driven ancient geodynamo. Could an increase in magnetic field strength as a consequence of inner core crystallization be related to the emergence of multi-cellular life in the geological record not long thereafter?

Natural Labs: Scientists Abroad Explore the Inner Workings of Our World

A helicopter carries heavy scientific equipment up Villarrica volcano as a team led by Hélène Le Mével prepares to install 8 microgravity sites, 6 seismometers, 5 infrasound sensors, 1 MultiGAS station, a GPS station, and a gravimeter on the volcano. More equipment, including a solar panel, can be seen in the foreground. Image credit: John West

This month also saw two major field programs in South America get underway.  One is the multi-year study of the Villarrica volcano in Chile sponsored by the Brinson Foundation and led by Hélène Le Mével in collaboration with Diana Roman and postdoctoral fellow Kathleen McKee.  Over the last couple of weeks of February, the team installed 8 microgravity sites, 6 seismometers, 5 infrasound sensors, 1 MultiGAS station, a GPS station, and a gravimeter.  Villarrica erupts frequently and currently has an active lava lake at the bottom of the crater.  McKee caught a stunning video of the crater and its lava lake when the team flew over the summit as they were installing instruments around the crater rim. 

The diverse instrumentation will remain on the volcano for almost a year, recording magma movements underground and gas emissions at the surface. The goal is to use this extensive dataset to better understand the physics of magma movement and the exsolution of gas from the magma, which are two parameters that control not only when an eruption will occur, but also the explosivity of that eruption.

MUSICA Underway

In February, Lara Wagner, Christy Till, Gaspar Monsalve, and Agustin Cardona traveled to Colombia to prepare for the upcoming MUSICA project. 

The other field program that started in February was Lara Wagner’s planned deployment of a large seismic array across Colombia.  The project, named MUSICA, will bring together an international team of Earth scientists with expertise in seismology, geochemistry, geochronology, and geodynamics to study the unique tectonic setting present in Colombia today.  The project also includes a plan to bring teachers along for the ride so that they can develop bilingual curricula for high school classes.

Lara’s project will use seismic waves to image the subducting plate as it travels beneath Colombia, providing critical information on at least two aspects of this process, the consequences of the water released by the oceanic plate on the continental plate, and the relative strength of the descending plate in comparison to the surrounding mantle.  The former addresses what will happen when the currently horizontally moving slab eventually steepens its plunge into Earth’s deep interior and is replaced by hot mantle that will interact with the wet, weak, potentially ore-metal-rich, and easily melted base of the continent formed during this period of horizontal subduction.  The latter is key information for understanding the dynamics of plate tectonics and the ultimate fate of these oceanic plates as they descend into Earth’s interior.

Richard Carlson, Director, Carnegie Earth and Planets Laboratory
Carnegie Institution for Science

Michael Walter, Deputy Director, Carnegie Earth and Planets Laboratory
Carnegie Institution for Science

 

March 2020 Newsletter

 

 



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