Question

Please read the following passage.

For decades, historians have predominantly attributed the rapid decline of the Harappan civilization in the Indus Valley to a massive, sudden environmental catastrophe. According to the traditional "tectonic hypothesis," severe earthquakes altered the courses of major rivers, leading to devastating floods that destroyed agricultural infrastructure. Proponents of this view argue that the abrupt abandonment of major urban centers, which lacked evidence of foreign invasion, could only be explained by an immediate, unmanageable environmental crisis. This theory remained virtually unchallenged throughout the twentieth century, largely because early archaeological excavations focused primarily on the structural damage and sediment deposits found in the upper layers of ruined cities, which seemed to corroborate the idea of sudden devastation.

Recently, however, advanced sediment analysis and sophisticated climate modeling have cast significant doubt on the tectonic hypothesis. Researchers analyzing riverbed core samples found that while river courses did indeed shift, these changes occurred gradually over several centuries rather than in a sudden, singular catastrophic event. Furthermore, paleobotanical evidence indicates a slow, deliberate transition in agricultural practices across the region. Farmers steadily shifted their focus from water-intensive winter crops, such as wheat and barley, to drought-resistant summer crops, like millet. This gradual agricultural adaptation strongly suggests that the civilization was proactively responding to a prolonged climatic shift over many generations rather than reacting to a sudden, apocalyptic disaster.

In light of this newly available scientific data, contemporary scholars have proposed the "aridity hypothesis" as a more accurate and comprehensive explanation for the Harappan decline. This theory posits that a gradual, widespread weakening of the summer monsoon system led to increasing aridity across the entire region. Rather than collapsing violently and vanishing, the Harappan people likely engaged in a strategic, decentralized migration toward the more fertile and reliable regions of the Ganges basin. This alternative framework not only accounts for the gradual changes observed in the agricultural record but also effectively explains the subsequent proliferation of smaller, localized settlements that appeared throughout the periphery as the large, centralized urban centers were slowly and peacefully abandoned.

The theoretical shift from the tectonic hypothesis to the aridity hypothesis represents a broader methodological evolution within the discipline of archaeology. By relying on interdisciplinary approaches that seamlessly combine traditional excavation techniques with isotopic analysis and high-resolution climate science, researchers can now construct significantly more nuanced and dynamic historical narratives. This essential paradigm shift encourages historians to view ancient societies not merely as passive victims of sudden geological events, but as resilient, intelligent communities capable of complex, long-term adaptation to dramatically changing environmental conditions.

Based on the passage above, arrange the following abstract descriptions of paragraph functions into the correct sequential order that reflects the overall logical structure of the passage.