Ash layers found within a stratigraphic sequence can

ash layers found within a stratigraphic sequence can provide absolute age data for sedimentary
rock units that do not contain radioactive isotopes and calibrate relative dating techniques. These
methods can also be used to determine ages of pluton emplacement.
Thermochemical techniques can be used to determine temperature profiles within the crust, the
uplift of mountain ranges, and paleotopography.

Fractionation of the lanthanide series elements is used to compute ages since rocks were
removed from the mantle.
Other methods are used for more recent events. Optically stimulated luminescence and
cosmogenic radionuclide dating are used to date surfaces and/or erosion rates. Dendrochronology
can also be used for the dating of landscapes. Radiocarbon dating is used for geologically young
materials containing organic carbon.
Geological development of an area
The geology of an area changes through time as rock units are deposited and inserted, and
deformational processes change their shapes and locations.
Rock units are first emplaced either by deposition onto the surface or intrusion into the overlying
rock. Deposition can occur when sediments settle onto the surface of the Earth and later lithify
into sedimentary rock, or when as volcanic material such as volcanic ash or lava flows blanket
the surface. Igneous intrusions such as batholiths, laccoliths, dikes, and sills, push upwards into
the overlying rock, and crystallize as they intrude.
After the initial sequence of rocks has been deposited, the rock units can be deformed and/or
metamorphosed. Deformation typically occurs as a result of horizontal shortening, horizontal
extension, or side-to-side (strike-slip) motion. These structural regimes broadly relate to
convergent boundaries, divergent boundaries, and transform boundaries, respectively, between
tectonic plates.
When rock units are placed under horizontal compression, they shorten and become thicker.
Because rock units, other than muds, do not significantly change in volume, this is accomplished
in two primary ways: through faulting and folding. In the shallow crust, where brittle
deformation can occur, thrust faults form, which causes deeper rock to move on top of shallower
rock. Because deeper rock is often older, as noted by the principle of superposition, this can
result in older rocks moving on top of younger ones. Movement along faults can result in
folding, either because the faults are not planar or because rock layers are dragged along,
forming drag folds as slip occurs along the fault. Deeper in the Earth, rocks behave plastically
and fold instead of faulting. These folds can either be those where the material in the center of
the fold buckles upwards, creating "antiforms", or where it buckles downwards, creating
"synforms". If the tops of the rock units within the folds remain pointing upwards, they are called
anticlines and synclines, respectively. If some of the units in the fold are facing downward, the