Recently, the research team of Professor Huang Fang from the School of Earth and Space Sciences, University of Science and Technology of China, and Professor Roberta L. Rudnick from the University of California, Santa Barbara, USA, have collaborated to determine that the continental crust dominated by felsic composition was formed 3 billion years ago through the study of vanadium (V) isotopes of moraine and igneous rocks. The relevant research results are published online in the Proceedings of the National Academy of Sciences. Since its formation 4.56 billion years ago, the Earth has undergone a long process of evolution and differentiation. Today's Earth is the only terrestrial planet in the solar system that has a felsic continental crust. The initial composition of the continental crust was mafic magma derived from the mantle, and plate movement led to further evolution of the continental crust and the formation of a large area of felsic continental crust. Changes in the chemical composition of the continental crust have important implications for the evolution of the Earth, plate motion, and habitability of planets. For decades, researchers have drawn two opposing understandings based on different methods. One is that since the early Archean, the continental crust has been dominated by felsic components; The second is that before the middle and late Archean, the composition of the continental crust was still dominated by mafic composition, and the transition from mafic to felsic composition occurred in the middle and late Archean to early Proterozoic. The main reason for the controversy lies in the multiplicity of geochemical indicators used, while vanadium isotopes provide a reliable method. The researchers first analyzed the vanadium isotope composition of calc-alkaline igneous rocks in the subduction zone, compared data from global tholeiites, calc-alkaline igneous rocks, and Archean greenstone belt igneous rocks, and found that the correlation between the vanadium isotope composition, silicon dioxide content, and magnesium oxide content of the igneous rocks was applicable to Archean samples after excluding samples with excessive crystallization of magnetite. In order to explore the changes in the composition of the continental upper crust over time, the researchers further measured the vanadium isotope composition of moraine rocks. Moraine rocks are often used to study the composition of the continental crust, but due to the influence of cementitious materials and weathering, their major elements cannot be directly used to indicate the composition of the continental crust. As one of the few teams in the world that have achieved high-precision vanadium isotope measurement, Huang Fang's previous research has shown that vanadium isotope composition is not susceptible to weathering, alteration, and modification. The vanadium isotope composition of moraine rocks can be used to directly calculate the main element content of their original rocks. Further, researchers combined the obtained linear relationship between the vanadium isotope composition of magmatic rocks, silicon dioxide content, and magnesium oxide content, and the vanadium isotope composition of moraine rocks to reconstruct the composition of the ancient continental upper crust. They found that during the Middle Archean era (3 billion years ago), the continental upper crust was dominated by mafic composition, while the transition from mafic to felsic crust occurred after 3 billion years ago. Researchers say this compositional shift may mark the beginning of global plate tectonics, indicating that the global plate tectonic movement could not have started earlier than 3 billion years ago. (Outlook New Era Network)