A large class of "evidences" presented by young-Earth advocates involve measuring rates of various Earth processes, then attempting to extrapolate them backwards for millions of years. Generally, the purpose is to show that the process in question would build up to absurdity if it were allowed to continue through "evolutionary timescales." The fallacy of most claims of this type is a failure to recognize the importance of equilibrium. Most processes on Earth are in a state of balance, in which one process (such as erosion of the continents) is counteracted by others (such as emplacement of new continental material by volcanoes and tectonic uplift). Generally, processes on Earth do not build up without limit, because there is always another process that opposes the build-up, leading to the establishment of equilibrium.
The method for dealing with young-Earth claims of this type is to look for the limiting process that imposes equilibrium. In some cases the balancing process has simply been overlooked, and the young-Earth claim is laid to rest by pointing it out. Other times the balancing process is not well understood or even unknown, which may seem to lend credence to young-Earth claims. However...[u]nless we can prove that no balancing process exists (and in most cases that cannot be done), we should adopt the working hypothesis that there is a yet-to-be-discovered process that provides the equilibrium. Examples of the One-Sided Equation Fallacy include the influx of magma on the Earth's crust, the erosion of sediment from continents, the maximum life of comets, and helium-4 in the atmosphere.[footnote 1]This same error is described by Christian physicist Roger Wiens in his helpful essay, 'Radiometric Dating: A Christian Perspective':
There are a number of parameters which, if extrapolated from the present without taking into account the changes in the Earth over time, would seem to suggest a somewhat younger Earth. These arguments can sound good on a very simple level, but do not hold water when all the factors are considered. Some examples of these categories are the decaying magnetic field (not mentioning the widespread evidence for magnetic reversals), the saltiness of the oceans (not counting sedimentation!), the sedimentation rate of the oceans (not counting Earthquakes and crustal movement, that is, plate tectonics), the relative paucity of meteorites on the Earth's surface (not counting weathering or plate tectonics), the thickness of dust on the moon (without taking into account brecciation over time), the Earth-Moon separation rate (not counting changes in tides and internal forces), etc. While these arguments do not stand up when the complete picture is considered, the case for a very old creation of the Earth fits well in all areas considered.Sarfati uses a one-sided approach in several places in his book, such as his arguments about:
- genetic entropy in chapter 4 (which fails to mention the balancing processes of synergistic epistasis and soft selection)
- ocean salinity in chapter 12 (which fails to mention the various processes by which oceans lose salinity)
- comets in chapter 12 (Sarfati acknowledges the Kuiper Belt and the Oort Cloud, but he is selective in the information he provides on them)
- Earth's magnetic field in chapter 12 (which mentions but fails to properly engage the evidence for multiple reversals of the Earth's magnetic field over long periods of time in the Earth's past - see here [though your eyes may not be able to handle the appalling design of that webpage]).
 Matthew Tiscareno, ‘Is There Really Scientific Evidence for a Young Earth?’ (2000) http://chem.tufts.edu/science/
 Roger Wiens, ‘Radiometric Dating: A Christian Perspective’ (2002) http://www.asa3.org/ASA/
 See here for an explanation: Ian Musgrave, ‘Where do comets come from?’ (2009) http://pandasthumb.org/