20. The Elements in Transition
Yesodei HaTorah 4:4
Since everything will decompose back into the four basic elements, why was Adam told that he would return to dust rather than to all four elements? This is because the major part of man's make-up comes from the element of earth.
Things that decompose do not turn directly back into the four basic elements. Rather, they decompose into something else, which then turns into another thing, until it ultimately reverts to the basic elements. Thus, there is a cycle in which things constantly return to their basic elemental states.
Yesodei HaTorah 4:5
The four basic elements are in constant flux in some portion but never in their entirety. For example, a portion of the earth that is in proximity to water dissolves into water. Similarly, a portion of the water that is close to the wind evaporates into wind. A portion of the wind that is close to fire changes into fire. Similarly, a portion of fire can change to wind, wind can condense into water, and water can solidify into earth. This cycle proceeds gradually. The entirety of a basic element will never change: all water will never become wind, all wind will not become fire, etc. This would be impossible because none of the basic elements could ever cease to exist completely. Accordingly, only a portion of the fire will change to wind and vice versa. Between any two of these elements, change occurs in a constant and repeating cycle.
Editor’s note: I am not able to explain the Rambam’s science. In Moreh Nevuchim, he is willing to disregard Talmudic dicta (3:14) and even Biblical verses (2:25) in favor of observable science when necessary. Readers are free to assume either that the Rambam was sharing the best science of his day, or that he is describing spiritual rather than physical phenomena.