(relative geologic timescale) (b) Absolute Dating Following the discovery of radioactivity in 1895, radiometric dating techniques were developed to determine the absolute ages, i.e. In the succession of strata, each layer represents the geographical conditions that occurred over that area at the time the layer was deposited.
Although some information can be gleaned from igneous and metamorphic rocks, these rock types mainly record events which took place at depth, and help us unravel plate tectonic events.
Much of the information available about surface events is linked to those rocks which formed at the surface, sedimentary rocks.
Cliffs, road cuts, and non-vegetated landscapes allow us glimpses into geology which is often hidden from view.
Cliffs and road cuts are "side views" or "geologic cross-sections" of the topography which show the relative positions of various rock layers and structures at a given spot.
The laws of physics and chemistry that governed geologic processes in the past are the same as those that govern processes now and in the future.
The geologic timescale is a chronology (calendar) of events on Earth based on obtaining ages of past events.
To review our principles of relative dating as applied to such geologic cross-sections, we will make use of a neat learning tool available on the Internet.
"Athro Limited" is a private company which provides education modules on the Internet.
Covering some 70% of the earth's surface, these rocks have two characteristics which are of central importance for time considerations.