2 + 2 = 4.
That is non-contingent. Adding two and two gives the same result no matter who does it, how they do it, where they do it, or when. The same goes for expressions such as 2 + X = 4, or 27/X = 4, etc.
This four-play is a metaphor for the deterministic, Laplacian, non-contingent ideal of science, where the right tools and sufficient information always give the same, correct result under any circumstances.
But a better metaphor for the actual practice of geosciences and other historical, field-based sciences, is that you find, or observe (evidence of) a four. Mathematically, of course, there are an infinite number of numerical operations that could produce a four. Even if you know that the four arose from, say, subtraction or exponentiation, the possibilities are still infinite.