Historical geology orpalaeogeology is a discipline that uses the principles and methods ofgeology to reconstruct thegeological history of Earth.[1] Historical geology examines the vastness of geologic time, measured in billions of years, and investigates changes in theEarth, gradual and sudden, over thisdeep time. It focuses on geological processes, such asplate tectonics, that have changed the Earth's surface and subsurface over time and the use of methods includingstratigraphy,structural geology,paleontology, andsedimentology to tell the sequence of these events. It also focuses on theevolution oflife during different time periods in thegeologic time scale.[2]
During the 17th century,Nicolas Steno was the first to observe and propose a number of basic principles of historical geology, including three key stratigraphic principles: thelaw of superposition, theprinciple of original horizontality, and theprinciple of lateral continuity.[3]
18th-century geologistJames Hutton contributed to an early understanding of theEarth's history by proposing the theory ofuniformitarianism, which is now a basic principle in all branches of geology. Uniformitarianism describes anEarth formed by the samenatural phenomena that are at work today, the product of slow and continuous geological changes.[4][5] The theory can be summarized by the phrase "the present is the key to the past."[6] Hutton also described the concept of deep time. The prevailing conceptualization of Earth history in 18th-century Europe, grounded in a literal interpretation ofChristian scripture, was that of a young Earth shaped bycatastrophic events. Hutton, however, depicted a very old Earth, shaped by slow, continuous change.[7]Charles Lyell further developed the theory of uniformitarianism in the 19th century.[8] Modern geologists have generally acknowledged that Earth's geological history is a product of both sudden, cataclysmic events (such asmeteorite impacts andvolcanic eruptions) and gradual processes (such as weathering, erosion, and deposition).
The discovery ofradioactive decay in the late 19th century and the development ofradiometric dating techniques in the 20th century provided a means of derivingabsolute ages of events in geological history.
Geology is considered a historical science; accordingly, historical geology plays a prominent role in the field.[9]
Historical geology covers much of the same subject matter as physical geology, the study of geological processes and the ways in which they shape the Earth's structure and composition. Historical geology extends physical geology into the past.[1]
Economic geology, the search for and extraction offuel andraw materials, is heavily dependent on an understanding of the geological history of an area.Environmental geology, which examines the impacts ofnatural hazards such asearthquakes andvolcanism, must rely on a detailed knowledge of geological history.
Layers of rock, orstrata, represent ageologic record of Earth's history. Stratigraphy is the study of strata: their order, position, and age.
Structural geology is concerned with rocks'deformational histories.
Fossils are organic traces of Earth's history. In a historical geology context, paleontological methods can be used to study fossils and their environments, including surrounding rocks, and place them within the geologic time scale.
Sedimentology is the study of the formation, transport, deposition, and diagenesis ofsediments.Sedimentary rocks, including limestone, sandstone, and shale, serve as a record of Earth's history: they contain fossils and are transformed by geological processes, such as weathering, erosion, and deposition, through deep time.
Historical geology makes use of relative dating in order to establish the sequence of geological events in relation to each another, without determining their specific numerical ages or ranges.[10]
Absolute dating allows geologists to determine a more precise chronology of geological events, based on numerical ages or ranges. Absolute dating includes the use ofradiometric dating methods, such asradiocarbon dating,potassium–argon dating, anduranium–lead dating.Luminescence dating,dendrochronology, andamino acid dating are other methods of absolute dating.[11]
The theory of plate tectonics explains how the movement oflithospheric plates has structured the Earth throughout its geological history.[12]
Weathering,erosion, anddeposition are examples of gradual geological processes, taking place over large sections of the geologic time scale. In therock cycle, rocks are continually broken down, transported, and deposited, cycling through three main rock types:sedimentary,metamorphic, andigneous.
Paleoclimatology is the study of past climates recorded in geological time.
| Eon | Era | Period | Epochs | Start |
|---|---|---|---|---|
| Phanerozoic | Cenozoic | Quaternary | Holocene | 0.0117 |
| Pleistocene | 2.558 | |||
| Neogene | Pliocene | 5.333* | ||
| Miocene | 23.030* | |||
| Paleogene | Oligocene | 33.9* | ||
| Eocene | 56.0* | |||
| Paleocene | 66.0* | |||
| Mesozoic | Cretaceous | Late Cretaceous | 100.5* | |
| Early Cretaceous | c. 145.0 | |||
| Jurassic | Late Jurassic | 163.5 ± 1.0 | ||
| Middle Jurassic | 174.1 ± 1.0* | |||
| Early Jurassic | 201.3 ± 0.2* | |||
| Triassic | Late Triassic | c. 235* | ||
| Middle Triassic | 247.2 | |||
| Early Triassic | 252.2 ± 0.5* | |||
| Paleozoic | Permian | 298.9 ± 0.2* | ||
| Carboniferous | Pennsylvanian | 323.2 ± 0.4* | ||
| Mississippian | 358.9 ± 0.4* | |||
| Devonian | 419.2 ± 3.2* | |||
| Silurian | 443.4 ± 1.5* | |||
| Ordovician | 485.4 ± 1.9* | |||
| Cambrian | 541.0 ± 1.0* | |||
| Proterozoic | Neoproterozoic | Ediacaran | Precambrian | c. 635* |
| Cryogenian | 850 | |||
| Tonian | 1000 | |||
| Mesoproterozoic | Stenian | 1200 | ||
| Ectasian | 1400 | |||
| Calymmian | 1600 | |||
| Paleoproterozoic | Statherian | 1800 | ||
| Orosirian | 2050 | |||
| Rhyacian | 2300 | |||
| Siderian | 2500 | |||
| Archean | Neoarchean | 2800 | ||
| Mesoarchean | 3200 | |||
| Paleoarchean | 3600 | |||
| Eoarchean | 4000 | |||
| Hadean | 4567 |
| Overviews | |
|---|---|
| History of geology | |
| Composition and structure | |
| Historical geology | |
| Dynamic Earth | |
| Water | |
| Geodesy | |
| Geophysics | |
| Applications | |
| Occupations | |
