of the Earth's surface with respect to the geoid. This is what we refer to as "surface uplift"; and surface uplift can be defined by averaging elevation and changes in elevation over surface areas of a specified size. The "uplift of rocks" refers to the displacement of rocks with respect to the geoid. The displacement of rocks with respect to the surface is called exhumation. This simple equation relates the three kinds of displacement: Surface uplift = uplift of rock - exhumation The term geoid is used above to mean mean sea level and makes a good frame of reference. A given displacement within this frame of reference allows one to quantify the amount of work being done against gravity. Measuring uplift and exhumation can be tricky. Measuring the uplift of a point requires measuring its elevation change – usually geoscientists are not trying to determine the uplift of a singular point but rather the uplift over a specified area. Accordingly, the change in elevation of all points on the surface of that area must be measured, and the rate of erosion must be zero or minimal. Also, sequences of rocks deposited during that uplift must be preserved. Needless to say, in mountain ranges where elevations are far above sea level these criteria are not easily met. Paleoclimatic restorations though can be valuable; these studies involve inferring changes in climate in an area of interest from changes with time of flora/fauna that is known to be sensitive to temperature and rainfall. The magnitude of the exhumation a rock has been subjected to may be inferred from geothermobarometry (measuring previous pressure and temperature history of a rock or assemblage). Knowing the pressure and temperature history of a region can yield an estimate of the ambient geothermal gradient and bounds on the exhumation process; however, geobarometric/geothermometric studies do not produce a rate of exhumation (or any other information on time). Exhumation rates can be inferred from fission tracks and from radiometric ages as long as a thermal profile can be estimated. References External links An explanation of tectonic forces Geomorphology Plate tectonics Mountain geomorphology