From Wikipedia, the free encyclopedia
Geology (from the
Greek γῆ,
gê, "earth" and λόγος,
logos, "speech") is the
science and study of the solid and liquid matter that constitutes the
Earth. The field of geology encompasses the study of the composition,
structure,
physical properties, dynamics, and
history of
Earth materials, and the processes by which they are formed, moved, and changed. The field is a major
academic discipline, and is also important for
mineral and
hydrocarbon extraction, knowledge about and mitigation of
natural hazards, some
engineering fields, and understanding
past climates and environments.
History and etymology
History
A mosquito and a fly in this
Baltic amber necklace are between 40 and 60 million years old
Some modern scholars, such as
Fielding H. Garrison, are of the opinion that modern geology began in the
medieval Islamic world.
[3] Abu al-Rayhan al-Biruni (973–1048 AD) was one of the earliest
Muslim geologists, whose works included the earliest writings on the
geology of India, hypothesizing that the
Indian subcontinent was once a sea.
[4] Ibn Sina (Avicenna, 981–1037), in particular, made significant contributions to geology and the natural sciences (which he called
Attabieyat) along with other
natural philosophers such as
Ikhwan AI-Safa and many others. He wrote an encyclopaedic work entitled “
Kitab al-Shifa” (the Book of Cure, Healing or Remedy from ignorance), in which Part 2, Section 5, contains his essay on Mineralogy and Meteorology, in six chapters: Formation of mountains, The advantages of mountains in the formation of clouds; Sources of water; Origin of earthquakes; Formation of minerals; The diversity of earth’s
terrain. These principles were later known in the
Renaissance of
Europe as the
law of superposition of strata, the concept of
catastrophism, and the doctrine of
uniformitarianism. These concepts were also embodied in the Theory of the Earth by
James Hutton in the Eighteenth century C.E. Academics such as
Toulmin and
Goodfield (1965), commented on Avicenna's contribution: "Around A.D. 1000, Avicenna was already suggesting a hypothesis about the origin of
mountain ranges, which in the Christian world, would still have been considered quite radical eight hundred years later".
[5] Avicenna's
scientific methodology of
field observation was also original in the Earth sciences, and remains an essential part of modern geological investigations.
[2]
In China, the
polymath Shen Kua (1031–1095) formulated a hypothesis for the process of land formation: based on his observation of fossil animal shells in a geological
stratum in a mountain hundreds of miles from the ocean, he inferred that the land was formed by erosion of the mountains and by
deposition of
silt.
Georg Agricola (1494–1555), a physician, wrote the first systematic treatise about
mining and
smelting works,
De re metallica libri XII, with an appendix
Buch von den Lebewesen unter Tage (Book of the Creatures Beneath the Earth). He covered subjects like
wind energy,
hydrodynamic power, melting cookers, transport of ores, extraction of
soda,
sulfur and
alum, and administrative issues. The book was published in 1556.
William Smith (1769–1839) drew some of the first geological maps and began the process of ordering
rock strata (layers) by examining the fossils contained in them.
[6]
James Hutton is often viewed as the first modern
geologist.
[7] In 1785 he presented a paper entitled
Theory of the Earth to the
Royal Society of Edinburgh. In his paper, he explained his theory that the Earth must be much older than had previously been supposed in order to allow enough time for mountains to be eroded and for
sediments to form new rocks at the bottom of the sea, which in turn were raised up to become dry land. Hutton published a two-volume version of his ideas in 1795 (
Vol. 1,
Vol. 2).
Followers of Hutton were known as
Plutonists because they believed that some rocks were formed by
vulcanism which is the deposition of lava from volcanoes, as opposed to the
Neptunists, who believed that all rocks had settled out of a large ocean whose level gradually dropped over time.
Sir Charles Lyell first published his famous book,
Principles of Geology[8], in 1830. Lyell continued to publish new revisions until he died in 1875. The book, which influenced the thought of
Charles Darwin, successfully promoted the doctrine of
uniformitarianism. This theory states that slow geological processes have occurred throughout the
Earth's history and are still occurring today. In contrast,
catastrophism is the theory that Earth's features formed in single, catastrophic events and remained unchanged thereafter. Though Hutton believed in uniformitarianism, the idea was not widely accepted at the time.
Much of 19th-century geology revolved around the question of the
Earth's exact age. Estimates varied from a few 100,000 to billions of years.
[9] The most significant advance in 20th century geology has been the development of the theory of
plate tectonics in the 1960s. Plate tectonic theory arose out of two separate geological observations:
seafloor spreading and
continental drift. The theory revolutionized the
Earth sciences.
Etymology
Geologic time
Geological time put in a diagram called a
geological clock, showing the relative lengths of the
eons of the Earth's history.
The geologic time scale encompasses the history of the Earth.
[11] It is bracketed at the young end by the dates of the earliest
solar system material at 4.567
Ga[12] (gigaannum: billion years ago) and the
age of the Earth at 4.54 Ga
[13][14], at the beginning of the informally-recognized
Hadean eon. At the young end of the scale, it is bracketed by the present day in the
Holocene epoch.
Important milestones
Brief time scale
The second and third timelines are each subsections of their preceding timeline as indicated by asterisks. The
Holocene (the latest
epoch) is too small to be shown clearly on this timeline.
Millions of Years
Relative and Absolute Dating
Geological events can be given a precise date at a point in time, or they can be related to other events that came before and after them. Geologists use a variety of methods to give both relative and absolute dates to geological events. They then use these dates to find the rates at which processes occur.
Relative dating
Methods for
relative dating were developed when geology first emerged as a
formal science. Geologists still use the following principles today as a means to provide information about geologic history and the timing of geologic events.
The principle of intrusive relationships concerns crosscutting
intrusions. In geology, when an
igneous intrusion cuts across a formation of
sedimentary rock, it can be determined that the igneous intrusion is younger than the sedimentary rock. There are a number of different types of intrusions, including stocks,
laccoliths,
batholiths,
sills and
dikes.
The principle of cross-cutting relationships pertains to the formation of
faults and the age of the sequences through which they cut. Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault. Finding the key bed in these situations may help determine whether the fault is a
normal fault or a
thrust fault.
[15]
The principle of inclusions and components states that, with sedimentary rocks, if inclusions (or
clasts) are found in a formation, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer. A similar situation with igneous rocks occurs when
xenoliths are found. These foreign bodies are picked up as
magma or lava flows, and are incorporated, later to cool in the matrix. As a result, xenoliths are older than the rock which contains them.
The principle of uniformitarianism states that the geologic processes observed in operation that modify the Earth's crust at present have worked in much the same way over geologic time.
[16] A fundamental principle of geology advanced by the 18th century Scottish physician and geologist
James Hutton, is that "the present is the key to the past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now."
[citation needed]
The principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds. Observation of modern marine and non-marine sediments in a wide variety of environments supports this generalization (although
cross-bedding is inclined, the overall orientation of cross-bedded units is horizontal).
[15]
The principle of superposition states that a sedimentary rock layer in a tectonically undisturbed sequence is younger than the one beneath it and older than the one above it. Logically a younger layer cannot slip beneath a layer previously deposited. This principle allows sedimentary layers to be viewed as a form of vertical time line, a partial or complete record of the time elapsed from deposition of the lowest layer to deposition of the highest bed.
[15]
The principle of faunal succession is based on the appearance of fossils in sedimentary rocks. As organisms exist at the same time period throughout the world, their presence or (sometimes) absence may be used to provide a relative age of the formations in which they are found. Based on principles laid out by
William Smith almost a hundred years before the publication of
Charles Darwin's
theory of evolution, the principles of succession were developed independently of evolutionary thought. The principle becomes quite complex, however, given the uncertainties of fossilization, the localization of fossil types due to lateral changes in habitat (
facies change in sedimentary strata), and that not all fossils may be found globally at the same time.
[17]
Absolute dating
Geologists can also give precise absolute dates to geologic events. These dates are useful on their own, and can also be used in conjunction with relative dating methods or to calibrate relative dating methods.
[18]
A large advance in geology in the advent of the 20th century was the ability to give precise absolute dates to geologic events through radioactive isotopes and other methods. The advent of
isotopic dating changed the understanding of geologic time. Before, geologists could only use fossils to date sections of rock relative to one another. With isotopic dates,
absolute dating became possible, and these absolute dates could be applied fossil sequences in which there was datable material, converting the old relative ages into new absolute ages.
Fractionation of the
lanthanide series elements is used to compute ages since rocks were removed from the mantle.
Geologic Materials
The majority of geological data come from research on solid Earth materials. These typically fall into one of two categories: rock and unconsolidated material.
Rock
This schematic diagram of the rock cycle shows the relationship between magma and sedimentary, metamorphic, and igneous rock
There are three major types of rock: igneous, sedimentary, and metamorphic. The
rock cycle is an important concept in geology which illustrates the relationships between these three types of rock, and magma. When a rock
crystallizes from melt (
magma and/or
lava), it is an
igneous rock. This rock can be
weathered and
eroded, and then
redeposited and
lithified into a sedimentary rock, or be turned into a
metamorphic rock due to heat and pressure that change the
mineral content of the rock and give it a characteristic
fabric. The sedimentary rock can then be subsequently turned into a metamorphic rock due to heat and pressure, and the metamorphic rock can be weathered, eroded, deposited, and lithified, becoming a sedimentary rock. Sedimentary rock may also be re-eroded and redeposited, and metamorphic rock may also undergo additional metamorphism. All three types of rocks may be re-melted; when this happens, a new magma is formed, from which an igneous rock may once again crystallize.
The majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth.
Unconsolidated material
Whole-Earth structure
Plate tectonics
On this diagram, subducting slabs are in blue, and continental margins and a few plate boundaries are in red. The blue blob in the cutaway section is the seismically-imaged
Farallon Plate, which is subducting beneath North America. The remnants of this plate on the Surface of the Earth are the
Juan de Fuca Plate and Explorer plate in the Northwestern USA / Southwestern Canada, and the
Cocos Plate on the west coast of Mexico.
The development of plate tectonics provided a physical basis for many observations of the solid Earth. Long linear regions of geologic features could be explained as plate boundaries.
[23] Mid-ocean ridges, high regions on the seafloor where
hydrothermal vents and volcanoes exist, were explained as
divergent boundaries, where two plates move apart. Arcs of volcanoes and earthquakes were explained as
convergent boundaries, where one plate
subducts under another.
Transform boundaries, such as the
San Andreas fault system, resulted in widespread powerful earthquakes. Plate tectonics also provided a mechanism for
Alfred Wegener's theory of
continental drift[24], in which the
continents move across the surface of the Earth over geologic time. They also provided a driving force for crustal deformation, and a new setting for the observations of
structural geology. The power of the theory of plate tectonics lies in its ability to combine all of these observations into a single theory of how the lithosphere moves over the convecting mantle.
Earth structure
Earth layered structure. (1) inner core; (2) outer core; (3) lower mantle; (4) upper mantle; (5) lithosphere; (6) crust
Earth layered structure. Typical wave paths from earthquakes like these gave early seismologists insights into the layered structure of the Earth
Seismologists can use the arrival times of
seismic waves in reverse to image the interior of the Earth. Early advances in this field showed the existence of a liquid
outer core (where
shear waves were not able to propagate) and a dense solid
inner core. These advances led to the development of a layered model of the Earth, with a
crust and
lithosphere on top, the
mantle below (separated within itself by
seismic discontinuities at 410 and 660 kilometers), and the outer core and inner core below that. More recently, seismologists have been able to create detailed images of wave speeds inside the earth in the same way a doctor images a body in a CT scan. These images have led to a much more detailed view of the interior of the Earth, and have replaced the simplified layered model with a much more dynamic model.
Mineralogists have been able to use the pressure and temperature data from the seismic and modelling studies alongside knowledge of the elemental composition of the Earth at depth to reproduce these conditions in experimental settings and measure changes in crystal structure. These studies explain the chemical changes associated with the major seismic discontinuities in the mantle, and show the crystallographic structures expected in the inner core of the Earth.
Geological evolution of an area
An originally horizontal sequence of sedimentary rocks (in shades of tan) are affected by
igneous activity. Deep below the surface are a
magma chamber and large associated igneous bodies. The magma chamber feeds the
volcano, and sends off shoots of
magma that will later crystallize into dikes and sills. Magma also advances upwards to form
intrusive igneous bodies. The diagram illustrates both a
cinder cone volcano, which releases ash, and a
composite volcano, which releases both lava and ash.
An illustration of the three types of faults. Strike-slip faults occur when rock units slide past one another, normal faults occur when rocks are undergoing horizontal extension, and thrust faults occur when rocks are undergoing horizontal shortening.
The geology of an area evolves through time as rock units are deposited and inserted and deformational processes change their shapes and locations.
When rock units are placed under horizontal
compression, they shorten and become thicker. Because rock units, other than muds,
do not significantly change in volume, this is accomplished in two primary ways: through
faulting and
folding. In the shallow crust, where
brittle deformation can occur,
thrust faults form, which cause deeper rock to move on top of shallower rock. Because deeper rock is often older, as noted by the
principle of superposition, this can result in older rocks moving on top of younger ones. Movement along faults can result in
folding, either because the faults are not planar, or because the rock layers are dragged along, forming drag folds, as slip occurs are along the fault. Deeper in the Earth, rocks behave
plastically, and fold instead of faulting. These folds can either be those where the material in the center of the fold buckles upwards, creating "
antiforms", or where it buckles downwards, creating "
synforms". If the tops of the rock units within the folds remain pointing upwards, they are called
anticlines and
synclines, respectively. If some of the units in the fold are facing downward, the structure is called an overturned anticline or syncline, and if all of the rock units are overturned or the correct up-direction is unknown, they are simply called by the most general terms, antiforms and synforms.
Even higher pressures and temperatures during horizontal shortening can cause both folding and
metamorphism of the rocks. This metamorphism causes changes in the
mineral composition of the rocks; creates a
foliation, or planar surface, that is related to mineral growth under stress; and can remove signs of the original textures of the rocks, such as
bedding in sedimentary rocks, flow features of
lavas, and crystal patterns in
crystalline rocks.
Extension causes the rock units as a whole to become longer and thinner. This is primarily accomplished through
normal faulting and through the ductile stretching and thinning. Normal faults drop rock units that are higher below those that are lower. This typically results in younger units being placed below older units. Stretching of units can result in their thinning; in fact, there is a location within the
Maria Fold and Thrust Belt in which the entire sedimentary sequence of the Grand Canyon can be seen over a length of less than a meter. Rocks at the depth to be ductilely stretched are often also metamorphosed. These stretched rocks can also pinch into lenses, known as
boudins, after the French word for "sausage", because of their visual similarity.
Where rock units slide past one another,
strike-slip faults develop in shallow regions, and become
shear zones at deeper depths where the rocks deform ductilely.
Geologic cross-section of
Kittatinny Mountain. This cross-section shows metamorphic rocks, overlain by younger sediments deposited after the metamorphic event. These rock units were later folded and faulted during the uplift of the mountain.
The addition of new rock units, both depositionally and intrusively, often occurs during deformation. Faulting and other deformational processes result in the creation of topographic gradients, causing material on the rock unit that is increasing in elevation to be eroded by hillslopes and channels. These sediments are deposited on the rock unit that is going down. Continual motion along the fault maintains the topographic gradient in spite of the movement of sediment, and continues to create accommodation space for the material to deposit. Deformational events are often also associated with volcanism and igneous activity. Volcanic ashes and lavas accumulate on the surface, and igneous intrusions enter from below.
Dikes, long, planar igneous intrusions, enter along cracks, and therefore often form in large numbers in areas that are being actively deformed. This can result in the emplacement of
dike swarms, such as those that are observable across the Canadian shield, or rings of dikes around the
lava tube of a volcano.
All of these processes do not necessarily occur in a single environment, and do not necessarily occur in a single order. The
Hawaiian Islands, for example, consist almost entirely of layered
basaltic lava flows. The sedimentary sequences of the mid-continental United States and the
Grand Canyon in the southwestern United States contain almost-undeformed stacks of sedimentary rocks that have remained in place since
Cambrian time. Other areas are much more geologically complex. In the southwestern United States, sedimentary, volcanic, and intrusive rocks have been metamorphosed, faulted, foliated, and folded. Even older rocks, such as the
Acasta gneiss of the
Slave craton in northwestern
Canada, the
oldest known rock in the world have been metamorphosed to the point where their origin is undiscernable without laboratory analysis. In addition, these processes can occur in stages. In many places, the Grand Canyon in the southwestern United States being a very visible example, the lower rock units were metamorphosed and deformed, and then deformation ended and the upper, undeformed units were deposited. Although any amount of rock emplacement and rock deformation can occur, and they can occur any number of times, these concepts provide a guide to understanding the
geological history of an area.
Methods of geology
Geologists use a number of field, laboratory, and numerical modeling methods to decipher Earth history and understand the processes that occur on and in the Earth. In typical geological investigations, geologists use primary information related to
petrology (the study of rocks),
stratigraphy (the study of sedimentary layers), and
structural geology (the study of positions of rock units and their deformation). In many cases, geologists also study modern
soils,
rivers,
landscapes, and
glaciers; investigate past and current life and
biogeochemical pathways, and use
geophysical methods to investigate the subsurface.
Field methods
A typical
USGS field mapping camp in the 1950's
Geological
field work varies depending on the task at hand. Typical fieldwork could consist of:
- Geological mapping[25]
- Structural mapping: the locations of the major rock units and the faults and folds that led to their placement there.
- Stratigraphic mapping: the locations of sedimentary facies (lithofacies and biofacies) or the mapping of isopachs of equal thickness of sedimentary rock
- Surficial mapping: the locations of soils and surficial deposits
- Surveying of topographic features
- Subsurface mapping through geophysical methods.[27]
- These methods include:
- They are used for:
- High-resolution stratigraphy
- Biogeochemistry and geomicrobiology[28]
- Collecting samples to:
- And to use these discoveries to
- Understand early life on Earth and how it functioned and metabolized
- Find important compounds for use in pharmaceuticals.
- Paleontology: excavation of fossil material
- Collection of samples for geochronology and thermochronology[29]
- Glaciology: measurement of characteristics of glaciers and their motion[30]
Laboratory methods
Petrology
Petrologists use
fluid inclusion data
[35] and perform high temperature and pressure physical experiments
[36] to understand the temperatures and pressures at which different mineral phases appear, and how they change through igneous
[37] and metamorphic processes. This research can be extrapolated to the field to understand metamorphic processes and the conditions of crystallization of igneous rocks.
[38] This work can also help to explain processes that occur within the Earth, such as
subduction and
magma chamber evolution.
Structural geology
A diagram of an orogenic wedge. The wedge grows through faulting in the interior and along the main basal fault, called the
décollement. It builds its shape into a
critical taper, in which the angles within the wedge remain the same as failures inside the material balance failures along the décollement. It is analogous to a bulldozer pushing a pile of dirt, where the bulldozer is the overriding plate.
Structural geologists use microscopic analysis of oriented
thin sections of geologic samples to observe the
fabric within the rocks which gives information about strain within the crystal structure of the rocks. They also plot and combine measurements of geological structures in order to better understand the orientations of faults and folds in order to reconstruct the history of rock deformation in the area. In addition, they perform analog and numerical experiments of rock deformation in large and small settings.
The analysis of structures is often accomplished by plotting the orientations various features onto
stereonets. A stereonet is a stereographic projection of a sphere onto a plane, in which planes are projected as lines and lines are projected as points. These can be used to find the locations of
fold axes, relationships between several faults, and relationships between other geologic structures.
Among the most well-known experiments in structural geology are those involving orogenic wedges, which are zones in which
mountains are built along
convergent tectonic plate boundaries.
[39] In the analog versions of these experiments, horizontal layers of sand are pulled along a lower surface into a back stop, which results in realistic-looking patterns of faulting and the growth of a
critically-tapered (all angles remain the same) orogenic wedge.
[40] Numerical models work in the same way as these analog models, though they are often more sophisticated and can include patterns of erosion and uplift in the mountain belt.
[41] This helps to show the relationship between erosion and the shape of the mountain range. These studies can also give useful information about pathways for metamorphism through pressure, temperature, space, and time.
[42]
Stratigraphy
Main article:
Stratigraphy
Exploration geologists examining a freshly recovered drill core.
Chile, 1994
In the laboratory, stratigraphers analyze samples of stratigraphic sections that can be returned from the field, such as those from
drill cores.
[43] Stratigraphers also analyze data from geophysical surveys that show the locations of stratigraphic units in the subsurface.
[44] Geophysical data and
well logs can be combined to produce a better view of the subsurface, and stratigraphers often use computer programs to do this in three dimensions.
[45] Stratigraphers can then use these data to reconstruct ancient processes occurring on the surface of the Earth,
[46] interpret past environments, and locate areas for water, coal, and hydrocarbon extraction.
In the laboratory,
biostratigraphers analyze rock samples from outcrop and drill cores for the fossils found in them.
[43] These fossils help scientists to date the core and to understand the
depositional environment in which the rock units formed. Geochronologists precisely date rocks within the stratigraphic section in order to provide better absolute bounds on the timing and rates of deposition.
[47] Magnetic stratigraphers look for signs of magnetic reversals in igneous rock units within the drill cores.
[43] Other scientists perform stable isotope studies on the rocks to gain information about past climate.
[43]
Planetary geology
Surface of Mars as photographed by the
Viking 2 lander December 9, 1977.
With the advent of
space exploration in the twentieth century, geologists have begun to look at other planetary bodies in the same way as the Earth. This led to the establishment of the field of
planetary geology, sometimes known as Astrogeology, in which geologic principles are applied to other bodies of the solar system.
Although the Greek-language-origin prefix
geo refers to Earth, "geology" is often used in conjunction with the names of other planetary bodies when describing their composition and internal processes: examples are "the
geology of Mars" and "
Lunar geology". Specialised terms such as
selenology (studies of the Moon),
areology (of Mars), etc., are also in use.
Although planetary geologists are interested in all aspects of the planets, a significant focus is in the search for past or present life on other worlds. This has led to many missions whose purpose (or one of their purposes) is to examine planetary bodies for evidence of life. One of these is the
Phoenix lander, which analyzed
Martian polar soil for water and chemical and mineralogical constituents related to biological processes.
Applied geology
Economic geology
Economic geologists help locate and manage the Earth's
natural resources, such as petroleum and coal, as well as mineral resources, which include metals such as iron, copper, and uranium.
Mining geology
Mining geology consists of the extractions of mineral resources from the Earth. Some resources of economic interests include
gemstones,
metals, and many minerals such as
asbestos,
perlite,
mica,
phosphates,
zeolites,
clay,
pumice,
quartz, and
silica, as well as elements such as
sulfur,
chlorine, and
helium.
Petroleum geology
Petroleum geologists study locations of the subsurface of the Earth which can contain extractable hydrocarbons, especially
petroleum and
natural gas. Because many of these reservoirs are found in
sedimentary basins[48], they study the formation of these basins, as well as their sedimentary and tectonic evolution and the present-day positions of the rock units.
Engineering geology
Engineering geology is the application of the geologic principles to engineering practice for the purpose of assuring that the geologic factors affecting the location, design, construction, operation and maintenance of engineering works are properly addressed.
In the field of
civil engineering, geological principles and analyses are used in order to ascertain the mechanical principles of the material on which structures are built. This allows tunnels to be built without collapsing, bridges and skyscrapers to be built with sturdy foundations, and buildings to be built that will not settle in clay and mud.
[49]
Hydrology and environmental issues
Main article:
Hydrogeology
Geology and geologic principles can be applied to various environmental problems, such as
stream restoration, the restoration of
brownfields, and the understanding of the interactions between
natural habitat and the geologic environment. Groundwater hydrology, or
hydrogeology, is used to locate groundwater,
[50] which can often provide a ready supply of uncontaminated water and is especially important in arid regions,
[51] and to monitor the spread of contaminants in groundwater wells.
[50][52]
Natural hazards
Main article:
Natural hazard
Geologists and geophysicists study natural hazards in order to enact safe
building codes and warning systems that are used to prevent loss of property and life.
[56] Examples of important natural hazards that are pertinent to geology (as opposed those that are mainly or only pertinent to meteorology) are:
Fields or related disciplines
Regional geology
By mountain range
By nations
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By planet
See also
Notes
- ^ Rudwick, M. J. S. (1985). The Meaning of Fossils: Episodes in the History of Palaeontology. University of Chicago Press. p. 24. ISBN 0226731030.
- ^ a b Munim M. Al-Rawi and Salim Al-Hassani (November 2002). "The Contribution of Ibn Sina (Avicenna) to the development of Earth sciences". FSTC. http://www.muslimheritage.com/uploads/ibnsina.pdf. Retrieved 2008-07-01.
- ^ Fielding H. Garrison wrote in the History of Medicine:
"The
Saracens themselves were the originators not only of
algebra,
chemistry, and geology, but of many of the so-called improvements or refinements of civilization, such as street lamps, window-panes, fireworks, stringed instruments,
cultivated fruits, perfumes, spices, etc."
- ^ Abdus Salam (1984), "Islam and Science". In C. H. Lai (1987), Ideals and Realities: Selected Essays of Abdus Salam, 2nd ed., World Scientific, Singapore, pp. 179–213.
- ^ Toulmin, S. and Goodfield, J. (1965), ’The Ancestry of science: The Discovery of Time’, Hutchinson & Co., London, p. 64 (see also The Contribution of Ibn Sina to the development of Earth sciences)
- ^ a b Simon Winchester ; (2002). The map that changed the world: William Smith and the birth of modern geology. New York, NY: Perennial. ISBN 0060931809.
- ^ James Hutton: The Founder of Modern Geology, American Museum of Natural History
- ^ Charles Lyell. (1991). Principles of geology. Chicago: University of Chicago Press. ISBN 9780226497976.
- ^ England, Philip (2007). "John Perry's neglected critique of Kelvin's age for the Earth: A missed opportunity in geodynamics". GSA Today 17: 4. doi:10.1130/GSAT01701A.1.
- ^ Winchester, Simon (2001). The Map that Changed the World. HarperCollins Publishers. pp. 25. ISBN 0-06-093180-9
- ^ International Commission on Stratigraphy
- ^ a b Amelin, Y; Krot, An; Hutcheon, Id; Ulyanov, Aa (Sep 2002). "Lead isotopic ages of chondrules and calcium-aluminum-rich inclusions.". Science (New York, N.Y.) 297 (5587): 1678–83. doi:10.1126/science.1073950. ISSN 0036-8075. PMID 12215641.
- ^ a b Patterson, C., 1956. “Age of Meteorites and the Earth.” Geochimica et Cosmochimica Acta 10: p. 230-237.
- ^ a b G. Brent Dalrymple (1994). The age of the earth. Stanford, Calif.: Stanford Univ. Press. ISBN 0804723311.
- ^ a b c Olsen, Paul E. (2001). "Steno's Principles of Stratigraphy". Dinosaurs and the History of Life. Columbia University. http://rainbow.ldeo.columbia.edu/courses/v1001/steno.html. Retrieved 2009-03-14.
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