“Sea pours out, from earth, and it measures up to the same amount it was before becoming earth.” (K 39; cp. R, S, DK 31b)
This passage has often been interpreted in concert with Fragment 38 (D 31A). Robinson follows Dehls/Kranz and lists this together with that earlier passage, as part (b) of Fragement 31. It has been common to interpret the passages as indicating that Heraclitus had a simple idea parallel to the conservation of mass. The amount of matter in the universe remains constant. It merely changes forms.
However, the passage is related to the earlier touched on discussion about whether fire is the Urstoff, which transforms into the other elements, perhaps in a well-ordered process, or whether the four elements exist eternally in a balance. Kahn and Robinson support the former view. In part this turns on their respective interpretations of the phrase “sea pours out from earth” as indicating a temporal ordering in the processes of the cosmic transformation of elements, with water coming after earth. Kahn argues for this view, pointing out that Heraclitus does also indicate “out of earth water is born” (DK & S 36) and earth is “death for water” (DK & S 36; cp. Kahn 144).
In line with Heraclitus’ multiple statements about a unity of opposites, we ought to highlight the harmony of oppositions here. Earth and water exist in balance. They are elements taken up in a law-like process, with bodies transforming from one element to another. The discussion of the ebb and flow of the seas, where seas pour out from earth, is at the very least an analogical expression of such a process.