How did Alexander von Humboldt's studies of Andean volcanoes challenge the Neptunist theory?

Alexander von Humboldt’s studies of Andean volcanoes provided critical evidence that challenged the Neptunist theory, which incorrectly asserted that Earth's surface was formed entirely through sedimentation from a primordial, universal ocean.12

During his expedition to South America, Humboldt’s observations of volcanic activity led him to conclude that eruptive forces and metamorphosis played a fundamental role in the development and ongoing evolution of the Earth's crust. By demonstrating that these geological features were the result of internal heat and volcanic processes rather than chemical precipitation from a liquid state, his findings helped disprove the Neptunist hypothesis. This work contributed to the shift in scientific thought toward a more dynamic understanding of Earth's history, moving away from the static, ocean-based models that had previously dominated geology.23