Without absolute ages, investigators could only determine which fossil organisms lived at the same time and the relative order of their appearance in the correlated sedimentary rock record.
Unlike ages derived from fossils, which occur only in sedimentary rocks, absolute ages are obtained from minerals that grow as liquid rock bodies cool at or below the surface.
Dating, in geology, determining a chronology or calendar of events in the history of Earth, using to a large degree the evidence of organic evolution in the sedimentary rocks accumulated through geologic time in marine and continental environments.
To date past events, processes, formations, and fossil organisms, geologists employ a variety of techniques.
With time, water-soluble “cement” will cause the sandy units to become sandstone.
Rocks of this kind in the ancient record may very well have resulted from rapid uplift and continent collision.The two approaches are often complementary, as when a sequence of occurrences in one context can be correlated with an absolute chronlogy elsewhere.Local relationships on a single outcrop or archaeological site can often be interpreted to deduce the sequence in which the materials were assembled.Where this occurs at the edge of a continent, as along the west coast of North and South America, large mountain chains develop with abundant volcanoes and their subvolcanic equivalents.These units, called igneous rock, or magma in their molten form, constitute major crustal additions.Similarly, in geologic studies, vast quantities of information from widely spaced outcrops have to be integrated.Some method of correlating rock units must be found.Just as the use of the fossil record has allowed a precise definition of geologic processes in approximately the past 600 million years, absolute ages allow correlations back to Earth’s oldest known rocks formed more than 4 billion years ago.In fact, even in younger rocks, absolute dating is the only way that the fossil record can be calibrated.Episodes of global volcanic activity, rifting of continents, folding, and metamorphism are defined by absolute ages.The results suggest that the present-day global tectonic scheme was operative in the distant past as well.plate tectonics has had a profound impact on the scientific understanding of our dynamic planet.