As Big History evolves beyond its original narrative structure, it must also evolve methodologically and pedagogically to equip learners with tools to understand multi-causal, dynamic, and emergent phenomena. This paper argues that Complex Systems Thinking (CST) provides a robust framework for reorienting Big History beyond a chronological “grand narrative” and toward a methodological paradigm capable of analyzing emergence, contingency, and feedback across scales. Drawing on the integration of CST within undergraduate biology curricula (Narguizian 2025), I demonstrate how students can engage major thresholds, not merely as historical events, but as emergent transitions resulting from structured interactions among components under specific energy and informational conditions. Focusing on biological thresholds such as the origin of life, the rise of multicellularity, and the Anthropocene, I argue that biology serves as a methodological bridge between cosmic, planetary, and cultural evolution. This approach reframes Big History as an epistemic practice grounded in systems reasoning and the Nature of Science (NOS), while also opening ethical and bioethical questions about information, agency, and technological power in the Anthropocene.