I want to add to this a more general note about “Uniformitarianism”, which is relevant to the blog post of @AdCaelumEo and a huge source of confusion among YECs these days.
References to Uniformitarianism are much, much more common in creationist literature than in actual science text books. It appears to me that YEC ministries are artificially inflating the importance of “Uniformitarianism” to mainstream scientific conclusions. They use it as a way to cast doubts on those conclusions, but it does not do justice to the actual scientific work. It’s comparable to the way they inflate the importance of “historical science” in a way that defies the actual reasoning behind these scientific findings. It’s mainly a rhetorical game.
Geologists do not use “Uniformitarianism” as a generalized a-priori starting point. Rather, they try to understand under which circumstances processes occur in rather predictable ways (“uniform”) and under which circumstances they don’t. In that sense, it’s more accurately seen as part of a specific hypothesis: “How well can I understand the available data if I assume erosive process A occurred uniformly over time period B?”
This point holds for all fields. In Astrophysics we’re often looking for opportunities to study processes that are relatively stable and predictable (for example, the lifetime of a main sequence star). But in order to find such opportunities consistently, we need to understand under which circumstances stability occurs. Therefore, it is never an a-priori assumption. It starts out as a hypothesis that needs theoretical and empirical support to avoid being discarded. It does not deserve the suffix “-ism” because it’s not a generalized approach. Especially since “Dynamicism” is at least as important. In addition to conditions of stability, astrophysicists have been very interested in studying dynamic transitions (for example, the different transitions in the lifetime of a star).
The teaching that “Uniformitarian beliefs” are the foundation of all old earth claims is false. Rather, scientists have empirical evidence and theoretical arguments which indicate when and why certain processes do or do not occur uniformly over time.