The location of the Flood/post-Flood boundary is an important issue for Flood geology because it is the starting point for a host of research questions. Many papers have been published on this topic, but its placement is still controversial. Three main views are advocated: a low Flood boundary in the Paleozoic or below, a boundary at or near the Cretaceous-Tertiary boundary (now the Cretaceous/Paleogene boundary), and a variable boundary towards the upper Cenozoic but with each geographical area to be evaluated on its merits.

In 2012, Marcus Ross, published a biostratigraphic analysis and argued that a Flood/post-Flood boundary at or near the Pliocene/Pleistocene on the geological column was untenable,1 and that the Cretaceous/Paleogene (or K/T) is the highest possible post-Flood boundary. In a brief letter exchange, Tasman Walker argued that the palaeontological data is biased by hidden assumptions, making Ross’s conclusions on the boundary premature. The two-stage letter exchange follows.