The structural, chemical, and thermal evolution of the deep Earth has modified both the power and shape of the geomagnetic field over time, and has left its paleomagnetic trace in rocks on the surface of our planet. This vast record holds the story of some of the most dramatic geological changes in the young and adolescent Earth (Landeau et al., 2022;Tarduno et al., 2020). However, reliable paleomagnetic records of these events have proven difficult to obtain and paleointensity studies are often plagued by large uncertainties and high failure rates, and frequently, the origin of the failure of recording fidelity remains poorly understood.Experimental protocols for determining the ancient field intensity rely on Néel's thermal activation theory (Néel, 1955(Néel, , 1988. Powerful as it is, it only applies to rocks containing uniformly magnetized, single-domain (SD) particles, with sizes smaller than ∼80 nm of equivalent spherical volume diameter (ESVD). Néel theory predicts that a thermoremanent magnetization (TRM) is acquired (blocked) at a temperature T b and is proportional to the geomagnetic field strength. Furthermore, this magnetization should be completely demagnetized by zero-field re-heating to an unblocking temperature T u , where T u = T b . When this is not the case, the remaining magnetization is referred to as a magnetic "tail." This "reciprocity" of blocking and unblocking (Thellier & Thellier, 1959) implies that the ancient field can be determined by replacing the original magnetization, across any temperature interval, with one generated in the laboratory. A related concept is that of "additivity" whereby the magnetization blocked when cooled from the Curie temperature T C , is the same as that acquired through heating and cooling steps at sequential temperature intervals up to T C .