When archaeomagnetic dating was still in its infancy, scientists attempting to develop the archaeomagnetic reference curve relied on archaeologists to provide an independent source of dating for the same contexts from which archaeomagnetic samples were collected. For example, archaeologists working in the American Southwest would collect both tree-ring samples and archaeomagnetic samples from the same ancient structures. If the latest tree-ring samples from a given context yielded dates ranging from, say, A.D. 860 to 862, then the particular magnetic alignment reflected in the archaeomagnetic samples collected from the same context could reasonably be inferred to date to approximately the same time. This process of correlating known and unknown dates for contexts in obvious association is called cross-dating.
Over several decades, the collection and cross-dating of thousands of archaeomagnetic and tree-ring samples led to the development of the reference curve. Today, in contexts that don’t yield other types of dating samples—but that have burned, clay-lined hearths—archaeologists can use the results of archaeomagnetic dating alone to date the contexts.