Relative dating earth
Biostratigraphy is the science of correlation of sedimentary units base on the identifiable fossils they contain.Paleontologists examine fossils of all kinds, but micropaleontology (the study of microscopic organisms) is perhaps the most useful method of dating because the remains of tiny organisms tend to be better preserved, more widely distributed, and may provide more precise age determinations than larger shells or bone material.
A geologic map or report typically is only a summary of investigations that frequently involve the collecting and processing of hundreds of rock samples, followed by the evaluation and interpretation of data from a variety of analytical techniques.A relative age is the age of a fossil organism, rock, or geologic feature or event defined relative to other organisms, rocks, or features or events rather than in terms of years.Tradition paleontological and biostratigraphic correlation methods are still perhaps the most common relative dating methods used by geologists.More modern correlation technologies include use of marine stable isotope records, paleomagnetic dating, tephrachronology, geomorphological methods, sedimentation characteristics, and other geochemical and radiometric methods.Relatively young deposits can be sometimes dated using tree rings, varved-lake sediments, coral growth patterns, and other methods.Paleontology is the study of life in past geologic periods (fossil plants and animals), incorporating knowledge of an organism's phylogeny, relationships to existing organisms, and correlation to an established chronology of Earth History.
Paleontology is limited to the study of sedimentary deposits where fossils are preserved, but can be used in establish relative ages of nearby igneous intrusion, faults, and other geologic features.
With the cumulative experience of centuries of paleontological research, the chronology of many fossil species are well established in context of both geologic time and distribution.
Geochronology is the science of dating and determining the time sequence of events in the history of the Earth.
This web page provides an overview of selected geochronology methods used by USGS scientists.
New dating methods are invented all the time, however, most have practical limitations.
Geologic research and mapping requires the determinations of the ages and composition of rocks.