Absolute datingAbsolute dating is the process of determining an age on a specified chronology in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy. Absolute dating provides a numerical age or range, in contrast with relative dating, which places events in order without any measure of the age between events.
Chronological datingChronological dating, or simply dating, is the process of attributing to an object or event a date in the past, allowing such object or event to be located in a previously established chronology. This usually requires what is commonly known as a "dating method". Several dating methods exist, depending on different criteria and techniques, and some very well known examples of disciplines using such techniques are, for example, history, archaeology, geology, paleontology, astronomy and even forensic science, since in the latter it is sometimes necessary to investigate the moment in the past during which the death of a cadaver occurred.
Relative datingRelative dating is the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age (i.e., estimated age). In geology, rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another. Prior to the discovery of radiometric dating in the early 20th century, which provided a means of absolute dating, archaeologists and geologists used relative dating to determine ages of materials.
Radiometric datingRadiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay.
Geological history of EarthThe geological history of Earth follows the major geological events in Earth's past based on the geological time scale, a system of chronological measurement based on the study of the planet's rock layers (stratigraphy). Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun, which also created the rest of the Solar System. Initially, the Earth was molten due to extreme volcanism and frequent collisions with other bodies.
GeologistA geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, although backgrounds in physics, chemistry, biology, and other sciences are also useful. Field research (field work) is an important component of geology, although many subdisciplines incorporate laboratory and digitalized work. Geologists can be classified in a larger group of scientists, called geoscientists.
History of EarthThe history of Earth concerns the development of planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to understanding of the main events of Earth's past, characterized by constant geological change and biological evolution. The geological time scale (GTS), as defined by international convention, depicts the large spans of time from the beginning of the Earth to the present, and its divisions chronicle some definitive events of Earth history.
StratigraphyStratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostratigraphy (lithologic stratigraphy), biostratigraphy (biologic stratigraphy), and chronostratigraphy (stratigraphy by age). Catholic priest Nicholas Steno established the theoretical basis for stratigraphy when he introduced the law of superposition, the principle of original horizontality and the principle of lateral continuity in a 1669 work on the fossilization of organic remains in layers of sediment.
Age of EarthThe age of Earth is estimated to be 4.54 ± 0.05 billion years (4.54 × 109 years ± 1%). This age may represent the age of Earth's accretion, or core formation, or of the material from which Earth formed. This dating is based on evidence from radiometric age-dating of meteorite material and is consistent with the radiometric ages of the oldest-known terrestrial material and lunar samples. Following the development of radiometric age-dating in the early 20th century, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old.
PalynologyPalynology is the study of microorganisms and microscopic fragments of mega-organisms that are composed of acid-resistant organic material and occur in sediments, sedimentary rocks, and even some metasedimentary rocks. Palynomorphs are the microscopic, acid-resistant organic remains and debris produced by a wide variety plants, animals, and Protista that have existed since the late Proterozoic.
ChronostratigraphyChronostratigraphy is the branch of stratigraphy that studies the ages of rock strata in relation to time. The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and eventually, the entire geologic record of the Earth. The standard stratigraphic nomenclature is a chronostratigraphic system based on palaeontological intervals of time defined by recognised fossil assemblages (biostratigraphy).
PaleoclimatologyPaleoclimatology (British spelling, palaeoclimatology) is the scientific study of climates predating the invention of meteorological instruments, when no direct measurement data were available. As instrumental records only span a tiny part of Earth's history, the reconstruction of ancient climate is important to understand natural variation and the evolution of the current climate. Paleoclimatology uses a variety of proxy methods from Earth and life sciences to obtain data previously preserved within rocks, sediments, boreholes, ice sheets, tree rings, corals, shells, and microfossils.
Last Glacial PeriodThe Last Glacial Period (LGP), also known colloquially as the Last Ice Age or simply Ice Age, occurred from the end of the Eemian to the end of the Younger Dryas, encompassing the period 115,000-11,700 years ago. The LGP is part of a larger sequence of glacial and interglacial periods known as the Quaternary glaciation which started around 2,588,000 years ago and is ongoing. The definition of the Quaternary as beginning 2.58 million years ago (Mya) is based on the formation of the Arctic ice cap.
PaleomagnetismPaleomagnetism (occasionally palaeomagnetism) is the study of magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called paleomagnetists. Certain magnetic minerals in rocks can record the direction and intensity of Earth's magnetic field at the time they formed. This record provides information on the past behavior of the geomagnetic field and the past location of tectonic plates.
BiostratigraphyBiostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. The primary objective of biostratigraphy is correlation, demonstrating that a particular horizon in one geological section represents the same period of time as another horizon at a different section. Fossils within these strata are useful because sediments of the same age can look completely different, due to local variations in the sedimentary environment.
ThermochronologyThermochronology is the study of the thermal evolution of a region of a planet. Thermochronologists use radiometric dating along with the closure temperatures that represent the temperature of the mineral being studied at the time given by the date recorded to understand the thermal history of a specific rock, mineral, or geologic unit. It is a subfield within geology, and is closely associated with geochronology.
LithostratigraphyLithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneous or sedimentary relating to how the rock was formed. Sedimentary layers are laid down by deposition of sediment associated with weathering processes, decaying organic matter (biogenic) or through chemical precipitation.
Marker horizonMarker horizons (also referred to as chronohorizons, key beds or marker beds) are stratigraphic units of the same age and of such distinctive composition and appearance, that, despite their presence in separate geographic locations, there is no doubt about their being of equivalent age (isochronous) and of common origin. Such clear markers facilitate the correlation of strata, and used in conjunction with fossil floral and faunal assemblages and paleomagnetism, permit the mapping of land masses and bodies of water throughout the history of the earth.
TephrochronologyTephrochronology is a geochronological technique that uses discrete layers of tephra—volcanic ash from a single eruption—to create a chronological framework in which paleoenvironmental or archaeological records can be placed. Such an established event provides a "tephra horizon". The premise of the technique is that each volcanic event produces ash with a unique chemical "fingerprint" that allows the deposit to be identified across the area affected by fallout.
