Apa itu Geology ?
Geologi berasal dari bahasa
Latin geo, "bumi" dan logos,"ilmu", yang mempelajari planet bumi
sebagai objeknya termasuk material pembentuknya, proses-proses yang mempengaruhi material
bumi, produk yang dihasilkan oleh bumi, serta sejarah dari dari planet ini termasuk mahluk
hidup yang pernah hidup sejak terbentuknya
Ahli geologi mempelajari komposisi dari materi bumi dan
segala macam proses geologi untuk menemukan dan mengeksploitasi sumberdaya mineral dari
bumi. Mereka juga meneliti gempabumi, gunung api dan bencana-bencana geologi lainnya untuk
memperkirakan dan menimalisasi dampak kerusakan dari gejala alam ini. Ahli geologi
meneliti sejarah geologi to melihat atau memperkirakan posisi benua serta samodra, to
mengetahui iklim masa lampau, dan juga mengikuti jejak evolusi kehidupan yang dijumpai
dalam rekaman-rekaman fosil.
Geologi tak terpisahkan dengan ilmu-ilmu yang
lain; Ilmu bumi (earth science) dan ilmu alam dasar overlap bertumpang
tindih dalam daerah penelitiannya. Misalnya, ilmu kimia dipakai untuk menganalisa batuan
dan mineral dari kerak bumi. Biologi membantu dalam mengetahui asal muasal organisme masa
lampau. Dimana, botani memberikan informasi tentang tumbuhan masa lampau, dan pengetahuan
zoologi sangat penting untuk mengetahui binatang masa lampau. Fisika membantu menerangkan
bermacam-macam tenaga fisik yang mempengaruhi bumi dan bagaimana pengaruh tenaga fisik ini
terhadap bumi dan bagaimana respon materi bumi terhadap gaya ini. Penemuan dari Astronomi
menunjukkan bagaimana bumi berinteraksi di tatasurya, astronomer juga berusaha untuk
menerangkan asal muasal bumi.
Bidang studi geologi
Bidang ilmu geologi mempunyai cakupan yang sangat luas, sehingga bisa dibagi menjadi dua
bagian utama: Geologi Fisik dan Sejarah
Geologi. Geologi fisik berhubungan dengan komposisi bumi, struktur yang
membentuknya, pergerakan dalam kerak bumi, dan proses yang terkait didalamnya baik masa
lampau, sedang terjadi dan perubahannya. Bidang studi utama dari Geologi Fisik termasuk
Mineralogi, mempelajari dan klasifikasi mineral; Petrologi, mempelajari asal muasal,
struktur, terdapatnya, dan sejarah dari batuan; Geologi Struktur, menyangkut deformasi
batuan dan bentuk bangunnya serta tatanannya.
is closely related to structural geology but generally treats the deformation and
historical evolution of the Earth's larger structural features. Geomorphology is
concerned with the general configuration of the Earth's surface and the origin,
development, and classification of landforms. Economic geology has to do with geologic
processes and materials that can be utilized by humans, and Geophysics and Geochemistry
rely on data derived from the study of the physics and chemistry of the Earth. More
specialized subfields of physical geology include seismology (the study of
Earthquakes and the Earth's interior), volcanology (the study of volcanoes and
volcanic phenomena), glaciology (see Glaciers and glaciation) and environmental
geology (geological studies related to human environmental concerns), engineering
geology (the application of the geological sciences to engineering practice), and
marine geology, or geological oceanography (that aspect of the study of the ocean
which deals specifically with the ocean floor and the ocean-continent margins).
Plate Tektonic (Tektonic Lempeng) berhubungan
dengan Geologi Struktur tetapi biasanya meneliti deformasi yang berhubungan dengan evolusi
bumi dalam skala ukuran yang sangat besar. Geomorfologi lebih terarah pada configrasi umum
dari bentuk permukaan bumi, asal terbentuknya, perkembangan dan klasifikasi bentuk roman
muka bumi. Geologi ekonomi mencakup pendayagunaan material bumi yang berhubungan dengan
kehidupan manusia. Sedangkan Geofisika dan Geokimia mendasarkan pada hasil pengkajian
fisika dan kimia dari bumi. Bidang studi khusus yang lebis spesifik dari Geologi Fisik
antara lain Seismologi (mempelajari gempa bumi dan struktur dalam dari bumi). Vulkanologi
(mempelajari gunung api dan fenomenanya), Glasiologi (mempelajari gletser dan proses
glasiasi), Geologi Lingkungan
Historical geology is concerned with the evolution of the Earth and its inhabitants from
their origin to the present day. Subfields include Stratigraphy, dealing with the
study, interpretation, and correlation of rock strata, and paleontology, the study of
prehistoric plants and animals as revealed by their fossils and related to the chronology
of the Earth's history. Geochronology is the study of time in relationship to the history
of the Earth, and Paleogeography deals with the physical geography of all or part
of the Earth's surface at some time in the geologic past. More specialized are Paleoclimatology
(the study of climates of the geologic past), Paleoecology (the study of the
relationship between ancient organisms and their environment), Paleomagnetism
(the study of the Earth's magnetic field over geologic time), and Micropaleontology
(the study of microscopically small fossils).
The major branches of historical geology--like those of physical geology--overlap in a
number of areas and are interdependent. Thus the unification of physical and historical
geology leads ultimately to a better understanding of the Earth.
HISTORY OF GEOLOGY
Although geology is a relatively young science, humans have long been interested in the
Earth. Prehistoric people utilized stones as tools and weapons, formed clay into pottery,
and sought shelter in rocky caves. But their knowledge of the Earth was restricted to the
ground beneath their feet or the limited areas that they could explore on foot.
Curiosity probably prompted early humans to pick up stones that later became tools. Fear
undoubtedly spurred speculation about such cataclysmic events as earthquakes and volcanic
eruptions. In early interpretations such geologic phenomena were explained by means of
unworldly or supernatural forces. According to an early Hindu legend, the Earth was
supported by eight elephants that stood on the back of a giant turtle. The turtle,
believed to be an incarnation of the god Vishnu, rested on the back of a coiled cobra, the
symbol of water. When any of these creatures moved, the Earth would vibrate, producing an
earthquake. In Japanese folklore, earthquakes are caused by a giant catfish that lives in
mud beneath the Earth. The fish can only be controlled while pinned beneath a huge
"keystone" possessing magical powers. When the catfish frees itself and thrashes
about, earthquakes are produced.
Ancient Greek and Roman Beliefs
As early as the 4th century BC, Aristotle taught that the Earth was a sphere. He also
believed that streams originated from springs and that minerals were formed from
"exhalations" of the Earth. He said that earthquakes were caused when
"pent-up" winds burst to the surface after being trapped in subterranean
Titus Lucretius Carus, an early Roman, wrote that quakes were caused by the collapse of
the roofs of great caverns. Other ancient Romans speculated about volcanic eruptions.
Indeed, the term volcano probably derives from the island of Vulcano, one of the Lipari
(Aeolian) Islands in the Tyrrhenian Sea. This island's active volcano was assumed to be
the home of Vulcan, Roman god of fire. Vulcan was the blacksmith of the gods, and when his
forge was heated, smoke issued from Vulcano's crater. The volcanic explosions were thought
to be caused by Vulcan pounding on his anvil.
Other ancients pondered the origin of fossils. In the 5th century BC, Anaximander of
Miletus noted fossil fish well above sea level and concluded that fish had been the
ancestors of all living things, including humans. Xenophanes of Colophon (5th century BC)
found fossils of marine organisms far inland and correctly inferred that they represented
the remains of sea-dwelling animals. Approximately 100 years later HERODOTUS of
Halicarnassus found nummulites (large foraminifera) in Egyptian limestones. He said that
these small, disk-shaped fossils were lentils left over from the slaves who built the
pyramids. Herodotus also stated that lower Egypt had been formed from sediment deposited
by the Nile. Because its roughly triangular shape resembles the Greek letter delta, he
named that region the delta. Today this term is used to describe similar river-laid
deposits in all parts of the world.
In the 4th century BC, Empedoced of Agrigentum recognized fossils in Sicily. He proposed
that plants, animals, and humans had appeared in this order because each depends on its
predecessor for survival--an "evolutionary" approach far ahead of its time.
Aristotle and Theophrastus of Lesbos also collected fossil fish, and the latter made one
of the earliest attempts to classify minerals.
There were few attempts to solve the Earth's mysteries during the Middle Ages. No
distinction was made between rocks, minerals, and fossils as the terms are now understood.
Early in the 11th century, however, AVICENNA, a Persian physician and Islamic scholar,
perceived basic geologic processes that were not to be understood for centuries. He
recognized water and wind as erosional agents, flooding of the land by prehistoric seas,
the development of solid rock from soft, water-deposited sediment, the formation of soils,
and fossils as the remains of ancient animals. Avicenna also grasped the importance of
time in geological processes. A less important contribution was made by Albertus Magnus, a
13th-century German scholar who wrote about rocks, minerals, and mountains.
The Renaissance: An Awakening
Interest in the Earth was rekindled early in the Renaissance by Leonardo Da Vinci. He
recognized the true nature of fossils and refuted the then-popular notions that fossils
were freaks of nature or devices that Satan had put in the rocks to lead people astray.
His approach to the study of the Earth was modern in that he explained features in the
rocks in the light of natural processes that could still be observed.
In the mid-16th century Georg Bauer, a German writing under the name of Georgius Agricola,
wrote on the origin of mountains, minerals, and underground water. Two of his books, De
natura fossilium (1546) and De re metallica (1556), laid the foundations for mineralogy
and mining geology.
The 17th Century
In 1667, Nicolaus STENO, a Danish physician and theologian, published the first true
treatise on geology. He wrote on processes of sedimentation, the origin of rocks, the
formation of crystals and fossils, and the interpretation of rock strata. His Prodromus
(1669) established criteria for differentiating between freshwater and marine sediments.
He was the first to recognize the principle of superposition--that the lower layers in a
sequence of rock strata must be older than those deposited above them. He also stated that
rock layers were formed from beds of sediment that were originally laid down in a nearly
horizontal position--the principle of original horizontality. Steno was also the first to
note that the crystal faces of a given mineral always have the same angle with respect to
one another. This is now known as the law of constancy of interfacial angles.
Despite advances in the 17th century, however, the concept of geologic time was not
understood. The creation of the Earth and the geologic record were still explained in
terms of biblical chronology. Accordingly, the creation was believed to have taken place
in 4004 BC, a date based on the calculations of James USSHER, a mid-17th-century Irish
18th- and 19th-Century Advances
Modern geologic thought began to develop in the 18th century and expanded steadily in the
19th. Benoit de Maillet, a French consul to Egypt, was probably the first to note that
older rocks contain fewer fossil species than do younger rocks. He also concluded that
layered rocks were deposited over long spans of time. In his Telliamed (de Maillet spelled
backward) he wrote of the formation of the Earth and of the origin of animals.
Giovanni Arduino, an Italian mineralogist, wrote on metamorphism and attempted to arrange
rocks chronologically from youngest to oldest. He classified them as "primitive"
or "primary," "secondary," and "tertiary." The last term is
still used today.
Two major geological controversies emerged during the late 18th century, both of which
were largely resolved by Scottish geologist James Hutton. The first centered on the
neptunism/plutonism debate. Proponents of neptunism, led by German mineralogist Abraham
Gottlob Werner, held that all bedrock had been precipitated in an ancient universal sea.
Accordingly, fossils were seen as victims of Noah's Flood, and granite and basalt were
believed to be the oldest deposits of an ancient sea. Proponents of plutonism, led by
Hutton, acknowledged that sedimentary buildup occurred but held that most rock had
solidified from an original molten mass. Neptunism was eventually discounted when granite
and basalt were proved to be igneous rocks.
The second controversy involved Catastrophism, a then widely held doctrine that the
Earth's major physical features were caused by periodic, worldwide catastrophes. Hutton
shared the belief that the Earth had undergone great changes, but he saw no concrete
evidence for catastrophism. He proposed that all past geologic events were somehow
connected, that the most important events occurred over immense time periods, and that
they continue to occur in the present. Hutton's concepts, which became known as
Uniformitarianism, established the significance of geologic time and provided the
cornerstone of future geologic thought.
Field studies and mapmaking burgeoned in the 19th century. William Smith, an English civil
engineer, observed that each layer of rock contained fossils characteristic of that
particular stratum and that such strata might be identified by their fossils and thus
correlated over wide areas. He laid the foundation for stratigraphical paleontology and
published the first geologic map of England. William Maclure, a Scottish geologist who
settled in Virginia, published the first maps of what was then the United States in 1809.
Near the end of the 19th century, geologists began to abandon a 6,000-year age for the
Earth, and many thought that the Earth was at least tens of millions of years old. In 1896
radioactivity was discovered by Henri Becquerel, a French physicist. This paved the way
for the 20th-century development of Radiometric Age-dating, which has found some rocks to
be 3.8 billion years old.
Geology in the 20th Century
With an understanding of geologic time and with Hutton's concept of uniformitarianism to
guide them, 20th-century geologists began to forge geology as it is known today.
Increasing knowledge of radioactive minerals, rates of decay, and decay products led to
the development of the long-awaited "geologic clock," which suggests that the
Earth is at least 4.6 billion years old. New sophisticated instruments and research
techniques have been developed; the Earth is now studied from ships, aircraft, and
In 1912, Alfred Wagoner, a German meteorologist, put forth his theory of Continental
drift. He proposed that a single protocontinent--Pangaea--had broken apart and the
fragments had drifted away to form the continents as they are known today. Wegener's
revolutionary proposal was rejected for decades, but in the early 1960s, geologist Harry
H. Hess and Robert S. Dietz, a geological oceanographer, developed the theory of Seafloor
Spreading. This theory, along with a better understanding of paleomagnetism, led to the
theory of plate tectonics, or global tectonics. This important and now widely accepted
theory assumes that the several moving plates of the Earth's crust are formed by volcanic
activity at the oceanic ridges and destroyed in great seafloor trenches at the margins of
the continents. One of the great geologic theories of all time, plate tectonics has
revolutionized geologic thought and stimulated global research.
The concept of plate tectonics has advanced research in marine geology, and special
attention is being directed to the ocean basins. Deep-sea cores recovered by research
vessels have confirmed seafloor spreading and yielded much information about the
composition and geologic history of the ocean floor. Studies of the continental shelves
have provided clues to valuable deposits of oil and natural gas. Radar and infrared
imagery from high-altitude aircraft and satellites are being used to study volcanoes and
potential earthquake faults and to locate accumulations of valuable mineral deposits.
In the laboratory, computer models are being developed to assist in solving geological
problems. The mass spectrometer, scanning electron microscope, and computerized axial
tomography are probing rocks, minerals, and fossils as geologists use evidence from the
past to understand the present and predict the future.
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Geological Sciences (1938; repr. 1990)
Dana, J. D., Geology (1849; repr. 1992);
Dean, D. R., James Hutton and the History of Geology
Dott, R. H., and Batten, R. L., Evolution of the
Earth, 4th ed. (1988);
Erickson, J., Fossils and Minerals:
Clues to the Earth's Past (1992);
Judson, S., et al., Physical Geology, 8th ed. (1989);
Levin, H. L., Contemporary Physical Geology, 3d ed.
(1990); and The Earth through Time, 4th ed. (1993);
Montgomery, C. W., Fundamentals of Geology (1993);
Skinner, B. J., and Porter, S. C., Dynamic Earth, 2d