Forensic reasoning about paleoclimatology

Human experts in many scientific fields routinely employ heuristics that are unproven and possible conclusions that are contradictory. We present a deployed software system for cosmogenic isotope dating, a domain that is fraught with these difficult issues. This system, which is called ACE ("age calculation engine"), takes as inputs the nuclide densities in a set of rock samples taken from a landform. It reasons from these data - which capture how long those rocks have been exposed to the sky - to answer the scientific question "What geological processes could have produced this distribution of nuclide concentrations, and over what time scales?" To do this, ACE employs an encoded knowledge base of the possible processes that may have acted on that landform in the past, complete with the mathematics of how those processes can affect samples, and it uses a custom workflow system to encode the computations associated with this scientific analysis. The system remains in active use to this day; the project website (ace.hwr.arizona.edu) has received over 17,000 hits since 2008 and the software (∼20,000 lines of python code) has been downloaded nearly 600 times as of April 2013, which is a significant number in a research community of O(10²) PI-level scientists.