The standard representation of the rock cycle usually looks like this:

enter image description here

Does each stage of the rock cycle currently balance? That is, are the various processes in dynamic equilibrium, so that the proportions of the different rock types remain constant?

If the processes are not in equilibrium, which types of rock are currently increasing in overall prevalence, and which are decreasing?

  • $\begingroup$ I'm not really sure what this is asking. Are you asking which rock forming processes is dominate on Earth? $\endgroup$
    – Neo
    May 5 '14 at 5:31
  • 4
    $\begingroup$ @Neo I have rewritten the question to make it clearer (I hope I haven't misconstrued the asker's meaning in doing so). I've also attempted an answer. I don't think that this question can be answered directly, but I nevertheless think it's useful in clearing up some simplifications and misconceptions. $\endgroup$
    – Pont
    May 5 '14 at 7:39
  • $\begingroup$ @Pont Thank you so much. I don't know English well :( You really makes it clearer. Thank you once again. $\endgroup$ May 5 '14 at 10:10

It's an interesting question, but in practice I think it's impossible to answer. It's very difficult to measure the rates of many of those processes, and the divisions between rock types can be quite ill-defined (for example, in migmatites). There's no scientific instrument we can point at a chunk of the earth which will tell us "in this region, 29.4 megatons of sedimentary rock became metamorphic rock during the past year".

What we can say, at least, is that the global balance of these processes is not constant over time. For example, during the Deccan Traps eruptions there was an increase in the rate of formation of igneous rock through solidification of magma.

The classic rock cycle diagram you posted probably encourages this kind of question, because it makes it look like a neat, closed system with well-defined boundaries and comparable quantities of each rock type. It's a very useful simplification for many purposes, but remember that these processes are occurring at or near the earth's surface. This whole system sits on top of the mantle (which is vast compared to the volume of crustal rock), and material is continually being passed between the two, so it's far from being a closed system.

  • $\begingroup$ +1 Excellent answer. $\endgroup$
    – Gimelist
    Nov 15 '14 at 9:34
  • $\begingroup$ How relatively important would events like the uplift of the Himalayas be (increasing erosion)? $\endgroup$ Jan 23 '18 at 21:17
  1. There is some studies pointing to a bigger activity of tectonism in Mid-Atlantic Ridges on ice ages. With more water freezed in south and north poles and less water in the ocean, the weight of water over South America plate(and others) are lower and the tectonics plates will be more active.

  2. In low rain periods, less chemical intemperism will happen(main source of sediments).

These factors and others more should modify the proportion of rock kinds.


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