Art by Noora Said.
How can we study crustal development?
Scientists have long sought to understand the development of the Earth—in particular, what exactly has allowed it to transform into the only known life-harboring planet? Yale graduate student Meng Guo and her advisor Jun Korenaga have aimed to build a piece of this complex puzzle in a recent publication in Science Advances. In the paper, Guo looks into understanding the development of Earth’s crust through a process known as argon degassing.
The development of Earth’s crust has been an important area of study since the 1960s; an accurate look into the evolution of crust can shed light on much about the geology and nature of early Earth. Because of this, there have been many different models made to try to accurately predict how Earth’s crust came to be; however, there has been tremendous variation in these estimates. To track the evolution of continental crust is a complicated task, with many different factors. “[Crustal development] contains two aspects: how the mass of continental crust has evolved through time and if the continental crust’s composition has significantly changed,” Guo said.
Previous attempts to constrain and detail this development have used a variety of methods, such as mantle-based methods, which directly track the loss of the mantle over time and inferring crustal evolution accordingly. “Geologists consider the mantle and crust as complementary, so they sum up to a constant volume. This means if you generate crust you have to lose the same amount of mantle. So, the mantle-based model is the most traditional and direct method,” Guo said. However, in order to bring a new perspective to this controversial topic, Guo looked to the changing argon content in the atmosphere to indirectly track crust development. When the Earth’s crust is created, noble gases are released and go off into the atmosphere, a process which is traceable. By tracking the concentration of argon in the atmosphere, her model would infer how the crust developed through time.
Guo’s model benefits from new data published in Nature in 2013, which provided estimates on the Archean atmospheric argon ratio using hydrothermal quartz. “Nobody can get a reasonable crust evolution throughout the entirety of Earth’s history using only today’s atmosphere composition,” Guo said. Thus, with this data as a source of argon concentrations in the distant past, along with the calculated current day concentration, Guo was now able to create this new constraint on her model.
Additionally, Guo’s model took a multidisciplinary approach and introduced a plethora of other constraints to calculate crust development, incorporating robust observations from geophysics, geochemistry, and geology. These were combined to produce a model for development which Guo believes gives a self-consistent story of continental formation. Her results indicate that there was rapid crustal growth during the early stages of Earth. The model also showed that the crust was potassium-rich during this period. Guo sees that this model will have important ramifications in further studies of plate tectonics, surface environment, and mantle convection for early Earth.
Navigating STEM: Meng Guo’s journey
Guo remarks that the geology department at Yale—recently renamed the “Department of Earth & Planetary Sciences”—was one of the first institutions in the United States where geology was taught. Guo is hopeful about the future of women in geology: “It’s a really good time for female scientists to thrive. People are more aware of the gender issue in academia, in STEM, and people are trying to embrace female scientists.” When she first matriculated at Yale for her PhD in geophysics in 2018, there were 10 new PhD students in her class and 6 were female. “Knowing how welcoming my department was to female PhDs was very nice,” she said.
When it comes to advice, Guo has one mantra she wants to pass onto younger students who may want to pursue a similar career path: “Explore any interest you have. Don’t think that if you get into this subject, this major, that this is what you’ll have to be for the rest of your life. Don’t think that way.” This advice is reflected in her own experience; Guo started by completing an undergraduate in chemistry, switched to geochemistry for her master’s, and is now studying geophysics for her Ph.D. Ultimately, she reflects that the hardest part of this journey was having to decide between staying with what was comfortable and risking pursuit of her dream. This choice presented itself when she was working a few years before her master’s degree, at a time when she was sure that current job would be her career.
“You’re facing a major life-changing decision and you have to know what you really want in life to make a decision that you won’t regret in the future,” Guo says. With the financial aid of the Fulbright Scholarship, she made the choice to quit her job and begin pursuing her master’s degree—bringing her to where she is today.
Looking to the future
She encourages students to pursue their interests in interdisciplinary spaces whenever possible. She attributes her success with this new argon degassing model to her past education. “If I hadn’t had the background in both geochemistry and geophysics, I wouldn’t have been able to build this cross-disciplinary model,” she said.
In the future, Guo is interested in building a new theoretical framework of coupled crust-mantle differentiation. She’d also like to conduct more careful geodynamical work to ascertain whether mantle convection had switched from a different, more archaic mode (involving stagnant-lid tectonics which was commonly believed to exist at the time) to modern plate tectonics during early Earth conditions, which is currently a highly debated topic in geoscience.
As mentioned in the paper, the most important feature of this argon model is the simultaneous application of multiple observational constraints to ensure the internal consistency and convergence of the known thermal evolution, crustal evolution and degassing history of the Earth. Just as she needed to combine these different aspects of the early Earth to successfully build her model, she reminds readers: “Don’t confine yourself, explore the interests you have, and you may be surprised where they lead you.” After all, it was this very intersection of her diverse perspectives and experiences in academia that led her to develop this new model indicating rapid crustal growth during the early ages of Earth.
About the Authors
Cindy Kuang is a sophomore in Timothy Dwight college, majoring in Neuroscience and History of Science, Medicine and Public Health. Outside of YSM, she is involved in the Chinese American Student Association, Asian American Health Advocates, Danceworks, and HAVEN Free Clinic.
Jerry Ruvalcaba is a sophomore MCDB major in Timothy Dwight college. Apart from writing for YSM, he’s involved in research at the Malvankar lab group where he focuses on elucidating the mechanisms by which Geobacter sulfurreducens bacteria are able to utilize electron nanowires.
The authors would like to acknowledge Meng Guo for her time and her enthusiasm for her research.
Guo, M., & Korenaga, J. (2020). Argon constraints on the early growth of felsic continental crust. Science Advances, 6(21), eaaz6234. https://doi.org/10.1126/sciadv.aaz6234
Guo, M. (2020, September 28). Argon constraints on the early growth of felsic continental crust [Online interview].
Korenaga, J. (2018). Crustal evolution and mantle dynamics through Earth history. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 376(2132), 20170408. https://doi.org/10.1098/rsta.2017.0408
Rosas, J. C., & Korenaga, J. (2018). Rapid crustal growth and efficient crustal recycling in the early Earth: Implications for Hadean and Archean geodynamics. Earth and Planetary Science Letters, 494, 42–49. https://doi.org/10.1016/j.epsl.2018.04.051
Sobolev, A. V., Asafov, E. V., Gurenko, A. A., Arndt, N. T., Batanova, V. G., Portnyagin, M. V., Garbe-Schönberg, D., Wilson, A. H., & Byerly, G. R. (2019). Deep hydrous mantle reservoir provides evidence for crustal recycling before 3.3 billion years ago. Nature, 571(7766), 555–559. https://doi.org/10.1038/s41586-019-1399-5
Pujol, M., Marty, B., Burgess, R., Turner, G., & Philippot, P. (2013). Argon isotopic composition of Archaean atmosphere probes early Earth geodynamics. Nature, 498(7452), 87–90. https://doi.org/10.1038/nature12152