earth's evolution through geologic time

   In the late 18th centry, James Hutton recognized the immensity of  Earth history and the importance of time as a component in all geological processes. In the 19th centry, Sir Charles Lyell and others effectively demonstrated that Earth had experienced many episodes of mountain building and erosion, which must have required great spans of geologic time.
    Most geologic processes that shape the surface of the earth and give structure to its interior operate over long time, up to millions and billions of years. The igneous, metamorphic, and sedimentary rocks exposed at the surface are the visible record of the geological processes of the past. From the time and space relations that those rocks manifest, geologist have built the geologic time scale, which is used for placing the geologic event of earth history in sequence according to ralative age. Spontaneous decay of radioactive atoms in rocks gives absolute ages that date the geologic period and the origin of the earth.
    The only record we have of things that happened on Earth in the geological past is the rocks that were preserved from erosional destrution. If we were drill a hole into any spot on Earth we would find the rock the carry the geologic history of that spot. The depper the hole, the older the rocks would be and the longer the history they would disclose.
    

   Fossil, the ramain or trace of prehistoric life, are important in clusions in sediment and sedmentary life, are important tools for interpreting the geologic past. The scientific of fossil is called paleontology. It is an interdisciplinary science that blends geology and biology in an attempt to understand all aspects of the succession of life over the vast expanse of geologic time. Knowing the nature of life forms that existed at a particular times helps researchers understand past environmental conditions. Furture, fossil are important time indicators and play a key role in correlating rocks of similar ages that are from different places.

 Geologists have divided the whole geologic history into units of varying magnitude. Together, they comprise the geologic time scale of  Earth history. the major units of the time scale were delineated during the 19th century, principlly by workers in western europe ang Great Britain. Because radiometric dating was unavialable at that time, the entire time scale was created using  methods of relating dating. It was only in 20th centry that radiometric methods permited numerical dates to be added.


   The geologic time scale divided Earth's history into units of varying magnitude. It is commonly presented in chart form, with the oldest time and the event at the bottom and the youngest at the top. the principle subdivisions of the geologic time scale, called eons, inculde the Archean, Proterozoic(together, those two erons are commonly referred to as the precambrian), and ,begining about 524million years ago, the Phanerozoic(meaning "visible life")eron is divided into the following eras:Paleozoic("ancient life"), Mesozoic("middle life"), and Cenozoic("recent life").