Historical geology

Geologic Time Spiral

Historical geology or palaeogeology is a discipline that uses the principles and methods of geology to reconstruct the geological history of Earth.<ref name=":0">Template:Cite book</ref> Historical geology examines the vastness of geologic time, measured in billions of years, and investigates changes in the Earth, gradual and sudden, over this deep time. It focuses on geological processes, such as plate tectonics, that have changed the Earth's surface and subsurface over time and the use of methods including stratigraphy, structural geology, paleontology, and sedimentology to tell the sequence of these events. It also focuses on the evolution of life during different time periods in the geologic time scale.<ref>Levin, Harold L.; King, David T. (2017). The Earth Through Time (11th ed.). Hoboken, New Jersey: John Wiley & Sons. p. 8. Template:ISBN.</ref>

Historical development

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: the law of superposition, the principle of original horizontality, and the principle of lateral continuity.<ref>Levin, Harold L.; King, David T. (2017). The Earth Through Time (11th ed.). Hoboken, New Jersey: John Wiley & Sons. p. 17. Template:ISBN.</ref>

18th-century geologist James Hutton contributed to an early understanding of the Earth's history by proposing the theory of uniformitarianism, which is now a basic principle in all branches of geology. Uniformitarianism describes an Earth formed by the same natural phenomena that are at work today, the product of slow and continuous geological changes.<ref>Template:Cite book</ref><ref>Template:Cite web</ref> The theory can be summarized by the phrase "the present is the key to the past."<ref>Levin, Harold L.; King, David T. (2017). The Earth Through Time (11th ed.). Hoboken, New Jersey: John Wiley & Sons. p. 20. Template:ISBN.</ref> Hutton also described the concept of deep time. The prevailing conceptualization of Earth history in 18th-century Europe, grounded in a literal interpretation of Christian scripture, was that of a young Earth shaped by catastrophic events. Hutton, however, depicted a very old Earth, shaped by slow, continuous change.<ref>Hutton, James (1788). "Theory of the Earth; or an Investigation of the Laws Observable in the Composition, Dissolution, and Restoration of Land upon the Globe." Transactions of the Royal Society of Edinburgh. Royal Society of Edinburgh. 1 (Part 2): 209–304.</ref> Charles Lyell further developed the theory of uniformitarianism in the 19th century.<ref>Template:Cite web</ref> Modern geologists have generally acknowledged that Earth's geological history is a product of both sudden, cataclysmic events (such as meteorite impacts and volcanic eruptions) and gradual processes (such as weathering, erosion, and deposition).

The discovery of radioactive decay in the late 19th century and the development of radiometric dating techniques in the 20th century provided a means of deriving absolute ages of events in geological history.

Use and importance

Geology is considered a historical science; accordingly, historical geology plays a prominent role in the field.<ref>Template:Cite journal</ref>

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.<ref name=":0" />

Economic geology, the search for and extraction of fuel and raw materials, is heavily dependent on an understanding of the geological history of an area. Environmental geology, which examines the impacts of natural hazards such as earthquakes and volcanism, must rely on a detailed knowledge of geological history.

Methods

Stratigraphy

Template:MainLayers of rock, or strata, represent a geologic record of Earth's history. Stratigraphy is the study of strata: their order, position, and age.

Structural geology

Template:MainStructural geology is concerned with rocks' deformational histories.

Paleontology

Template:MainFossils 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

Sedimentology is the study of the formation, transport, deposition, and diagenesis of sediments. 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.

Relative dating

Template:Main 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.<ref>Template:Cite web</ref>

Absolute dating

Template:Main Absolute dating allows geologists to determine a more precise chronology of geological events, based on numerical ages or ranges. Absolute dating includes the use of radiometric dating methods, such as radiocarbon dating, potassium–argon dating, and uranium–lead dating. Luminescence dating, dendrochronology, and amino acid dating are other methods of absolute dating.<ref>Template:Cite web</ref>

Plate tectonics

The theory of plate tectonics explains how the movement of lithospheric plates has structured the Earth throughout its geological history.<ref>Levin, Harold L.; King, David T. (2017). The Earth Through Time (11th ed.). Hoboken, New Jersey: John Wiley & Sons. p. 9. Template:ISBN.</ref>

Weathering, erosion, and deposition

Weathering, erosion, and deposition are examples of gradual geological processes, taking place over large sections of the geologic time scale. In the rock cycle, rocks are continually broken down, transported, and deposited, cycling through three main rock types: sedimentary, metamorphic, and igneous.

Paleoclimatology

Paleoclimatology is the study of past climates recorded in geological time.

Brief geological history

Eon	Era	Period	Epochs	Start
rowspan="22" style="background:Template:Period color" | Phanerozoic	rowspan="7" style="background:Template:Period color" | Cenozoic	rowspan="2" style="background:Template:Period color" | Quaternary	style="background:Template:Period color" | Holocene	0.0117
style="background:Template:Period color" | Pleistocene	2.558
rowspan="2" style="background:Template:Period color" | Neogene	style="background:Template:Period color" | Pliocene	5.333*
style="background:Template:Period color" | Miocene	23.030*
rowspan="3" style="background:Template:Period color" | Paleogene	style="background:Template:Period color" | Oligocene	33.9*
style="background:Template:Period color" | Eocene	56.0*
style="background:Template:Period color" | Paleocene	66.0*
rowspan="8" style="background:Template:Period color" | Mesozoic	rowspan="2" style="background:Template:Period color" | Cretaceous	style="background:Template:Period color" | Late Cretaceous	100.5*
style="background:Template:Period color" | Early Cretaceous	c. 145.0
rowspan="3" style="background:Template:Period color" | Jurassic	style="background:Template:Period color" | Late Jurassic	163.5 ± 1.0
style="background:Template:Period color" | Middle Jurassic	174.1 ± 1.0*
style="background:Template:Period color" | Early Jurassic	201.3 ± 0.2*
rowspan="3" style="background:Template:Period color" | Triassic	style="background:Template:Period color" | Late Triassic	c. 235*
style="background:Template:Period color" | Middle Triassic	247.2
style="background:Template:Period color" | Early Triassic	252.2 ± 0.5*
rowspan="7" style="background:Template:Period color" | Paleozoic	style="background:Template:Period color" | Permian	style="background:Template:Period color" |	298.9 ± 0.2*
rowspan="2" style="background:Template:Period color" | Carboniferous	style="background:Template:Period color" | Pennsylvanian	323.2 ± 0.4*
style="background:Template:Period color" | Mississippian	358.9 ± 0.4*
style="background:Template:Period color" | Devonian	style="background:Template:Period color" |	419.2 ± 3.2*
style="background:Template:Period color" | Silurian	style="background:Template:Period color" |	443.4 ± 1.5*
style="background:Template:Period color" | Ordovician	style="background:Template:Period color" |	485.4 ± 1.9*
style="background:Template:Period color" | Cambrian	style="background:Template:Period color" |	541.0 ± 1.0*
rowspan="10" style="background:Template:Period color" | Proterozoic	rowspan="3" style="background:Template:Period color" | Neoproterozoic	style="background:Template:Period color" | Ediacaran	rowspan="15" style="background:Template:Period color" | Precambrian	c. 635*
style="background:Template:Period color" | Cryogenian	850
style="background:Template:Period color" | Tonian	1000
rowspan="3" style="background:Template:Period color" | Mesoproterozoic	style="background:Template:Period color" | Stenian	1200
style="background:Template:Period color" | Ectasian	1400
style="background:Template:Period color" | Calymmian	1600
rowspan="4" style="background:Template:Period color" | Paleoproterozoic	style="background:Template:Period color" | Statherian	1800
style="background:Template:Period color" | Orosirian	2050
style="background:Template:Period color" | Rhyacian	2300
style="background:Template:Period color" | Siderian	2500
rowspan="4" style="background:Template:Period color" | Archean	style="background:Template:Period color" | Neoarchean		2800
style="background:Template:Period color" | Mesoarchean	3200
style="background:Template:Period color" | Paleoarchean	3600
style="background:Template:Period color" | Eoarchean	4000
style="background:Template:Period color" | Hadean			4567

External links

• Geology – Earth history | Encyclopedia Britannica
• Historical Geology | OpenGeology.org
• GEOL 102 Historical Geology | Lecture notes for course at the University of Maryland