Abductive reasoning is central to reconstructing the past in the geosciences. This paper outlines the nature of the abductive method and restates it in Bayesian terms. Evidence plays a key role in this working method and, in particular, traces of the past are important in this explanatory framework. Traces, whether singularly or as groups, are interpreted within the context of the event for which they have evidential claims. Traces are not considered as independent entities but rather as inter-related pieces of information concerning the likelihood of specific events. Exemplification of the use of such traces is provided by dissecting an example of their use in the environmental reconstruction of mountain climate.Keywords Geoscience . Bayesian . Abduction Geosciences, which encompass geology, physical geography, ecology and other field-based studies, as well as modelling and simulation studies of the physical environment, have long looked to the 'hard' sciences for their philosophical basis (e.g. Harvey 1969; Haines-Young and Petch 1986; von Engelhardt and Zimmerman 1988). Explanation is usually expressed in terms of a tri-form structure (Tucker 2004a). The tri-form structure of explanation consists of, firstly, a description of the event that is to be explained, the explanandum, secondly, a description of events that explain the event, the explanans, and, thirdly, something connecting the two together, be it a process, a mechanism or a 'law' or even a probabilistic relation or statistical generalization. This explanatory structure, and in particular, its development within a critical rationalist framework (Haines-Young and Petch 1986) has been seen by some researchers as being the way to understanding even though field investigations have tended to fall short of the ideals of this approach. Specifically, Philosophia (2008) 36:495-507