CAREER:Exploring the early Earth with high-resolution paleomagnetism

Harvard University, Cambridge MA

Investigators

Abstract

Conditions on the Earth during the first two billion years of its history (4.5 to 2.5 billion years before present) were vastly different from the modern Earth. Key events in Earth history, including the rise of life and the creation of continents, took place during this time, yet fundamental questions remain unanswered. Did the early Earth exhibit the familiar patterns of continental drift as we see today? When did the first oxygen-producing organisms evolve? Did a global magnetic field similar to that of the present-day isolate the atmosphere from loss to the solar wind? This project will use a new generation magnetic field imaging device, recently developed from advances in quantum sensing, to examine the magnetic properties of rock samples between 2.7 and 4.2 billion years in age. These experiments are expected to yield new insights into the initiation of plate tectonics, the evolution of the early atmosphere, and the rise of oxygen-producing life. In parallel with these measurements this project will develop a series of lessons with Boston-area middle school teachers involving student-led observations of the sun through solar telescopes distributed to the schools. These observations will serve as an introduction to changes in the sun's properties through time and its impact on surface conditions on the early Earth. The fundamental challenge to understanding conditions on Earth during the Archean Eon (4.0-2.5 billion years ago, or Ga) is the lack of well-preserved rocks dating from that time. Consequently, attempts to recover information about ancient magnetic fields have been severely hampered by pervasive remagnetization through metamorphism and chemical alteration of ferromagnetic phases. This project will apply a recently developed technology for micrometer-scale magnetic imaging, known as the quantum diamond microscope (QDM), to address major outstanding questions in Archean Earth history. The high spatial resolution of the QDM permits direct imaging of remanent magnetization carriers in complex, altered rocks, which aids the identification of primary paleomagnetic signals. In Task 1, the QDM will be used to infer the existence of the geodynamo before 3.5 Ga by recovering magnetic signals from a newly discovered population of 3.3-4.2 Ga zircons from the Barberton Greenstone Belt (BGB) of South Africa. As part of Task 2, the project team will apply both QDM and traditional paleomagnetic techniques on carefully selected igneous rock units to quantify the mobility of lithospheric plate at 3.45 Ga. Finally, Task 3 of the project will use the QDM to infer the origin of ferromagnetic iron oxides preserved in 2.78 Ga micrometeorites, thereby testing the controversial hypothesis that the upper atmosphere of the Earth was oxygen-rich several hundred million years before the Great Oxidation Event. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.