GEY102 Introduction to Geology PDF

GEY102- Introduction to Geology A lecture note by; Prof. M.E.Nton Department of Geology, University of Ibadan 1 Nature and scope of Geology 2 What is Geology? To the geologist, the earth is...

GEY102- Introduction to Geology A lecture note by; Prof. M.E.Nton Department of Geology, University of Ibadan 1 Nature and scope of Geology 2 What is Geology? To the geologist, the earth is not simply the globe upon which we live; it is an  Geology is derived from the ever-present challenge to learn more Greek ``geo’’, meaning about such things as earthquakes, ``earth’’, plus logos, meaning volcanoes, glaciers, and the meaning of ``discourse’’. This is briefly fossils. described as the study of the earth How old is the earth? Where did it come from? Of what is it made ? To answer  Widely, it is described as the these questions, the earth scientist must study of the physical features study the evidences of events that of the earth, the composition occurred millions of years ago. and structures of the rocks composing it, the forces at He must relate his findings to the results work in altering it and the of similar events that are happening records of animals and plants today. that had lived in it. In pursuing his study of the earth, the geologist To understand the nature3 relies heavily on other basic sciences. of prehistoric plants and For example, astronomy (the study of the nature and movements of planets, stars and other animals, we must turn to heavenly bodies) tells us where the earth fits into the universe and also suggests several theories as to the origin of our planet.  BIOLOGY, the study of all living forms. Chemistry (the study of the composition of substances and the changes which they undergo)  Zoology provides us with information about is used to analyze and study the rocks and the animals and minerals of the earths ’crust.  Botany gives us some insight into the nature of ancient plants. The science of physics (the study of matter and motion) helps to explain the various physical forces affecting the earth and the reaction of the  By using these sciences as well as others, the earths ’materials to the forces. geologist is better able to cope with the many complex problems that are inherent in the study of the earth and its history. The scope of geology is so broad that it has been split into two major divisions; physical and historical geology. 4 The term Earth Science, is commonly used in conjunction with the study of the earth. Although earth science Geology is related to civil engineering. Site for dams is includes the study of geology, it also the work of a geologist. encompasses the science of Meteorology (study of the atmosphere), Oceanography  Rocks are defined as aggregate of minerals (study of the oceans), and astronomy. and minerals are substances that have definite shapes called crystals. The study of rocks in the widest form –  Examples of minerals are calcite, feldspars, composition, origin and texture is quartz etc. called Petrology.  The study of minerals is called Mineralogy. The Thus we have; sedimentary, igneous study of crystal forms is known as and metamorphic petrology. Crystallography. Sedimentology or Sedimentary Petrology is the study of the sedimentary processes ( origin), composition and deposition of sedimentary rocks.  Economic Geology is the study of economic  Geochemistry is the study of the products of the earths’ crust and their chemistry of the natural materials found applications for commercial and industrial on the earths’ crust-in minerals, ores, 5 purposes. Included here for example are the rocks, soils and water bodies. important fields of mining and petroleum geology.  Geophysics is the study of the physics of the earth , i.e. the resistivity, magnetic  Mining Geology is the study of the qualitative properties of the earth. characteristics of minerals and the acts of exploitation them.  Structural geology is the study of the definite arrangement of rocks, rivers,  Petroleum Geology involves the study of the valleys, faults etc of the earth in their origin, occurrence and exploitation of initial state. petroleum and natural gas.  The study of the global arrangements of  The study of surface and under ground rocks i.e. their forms and structures is water is called Hydrogeology. called Tectonics or Geotectonics.  Engineering Geology is the application of  The origin of the surface features of the principles of geology to solving engineering earth is the field of Geomorphology. problems.  Photo Geology involves the use of aerial photography in deducing the geology of an area.  Remote Sensing relates to acquisition of information and data by interpretation from recording devices carried by aircrafts and satellites about ground features without coming into physical contact.  A new developed airborne tool of remote sensing using laser pulses called LiDAR (Light Detection and Ranging) has been developed which can see the ground through a tree cover.In combination with GPS, it is an important tool for detecting faults and measuring ground elevation.  The study of all aforementioned part is called physical geology 6  Medical Geology is the newest discipline of geology in which rocks and minerals are evaluated with respect to the health of living things, mainly humans. It involves such studies as toxicity of elements (such as trace elements) found in the earths’ crust and how they impact nutrition or geographic pattern of diseases.  Environmental Geology comes into play in studying the impact of engineering and mining projects on the environment, such as on human health, safety and well-being and also protection of ecosystems. Geological studies may also cover earthquakes, tsunamis, and landslides etc, which have enormous influence on the environment, particularly along sea coasts.  Oceanography and Marine Geology- Oceanography is the scientific study of the oceans in all aspects. Marine Geology involves the study of the structure of the ocean floor and ocean-continental borders. It involves study of the relief features, the rocks and sediments, their geochemistry, along with study and exploration of valuable minerals, including hydrocarbon, found in them. It also involves enquiry into depositional processes of waves and currents. 7  When sedimentary rocks are studied The study of past lives (fossils) such as in including the fossil contents, we are able to  knowing the distribution, ecology and 8 lay them in their order of succession. This evolution is known as Palaeontology. study is called Stratigraphy.  Geology is also associated with the scientific study of lakes, ponds and other confined  Historical Geology is a wider scope than water bodies with respect to their physical, Stratigraphy as it includes not only the chemical, biological and ecological succession of the strata and living things, attributes; this area is called Limnology. but also the entire history of the Earth, from its origin to developments right  Most elementary rocks contain radioactive through present. Of course, stratigraphy is elements e.g. carbon, rubidium, potassium an essential part, but the subject includes etc. The radioactive and stable isotopes of evolution of life forms, tectonism and all certain elements together with the rocks are other processes and events that created used in successfully determining absolute the present features of the Earth. ages of rocks and the nature of the earth in aspect of geology called Geochronology or isotope Geology. Such study is also useful in the determination of the origin, mechanisms and conditions of some geologic processes.  APPLICATIONS OF GEOLOGY 9  Geology is very important to the  Geologic principles solve needs of man. The search for fuel engineering problems such as and mineral deposits has shown some progress by the roles of in site selection for geologists. constructing railway lines, dams, hydroelectricity power, determining the strength of  The study of geology, more particularly through its fossil record rocks for putting up buildings, helps in understanding the process etc. of natural evolution.  It helps to forecast certain  It helps to combat the problems of natural calamities such as water supply earthquakes.  Principal Divisions of the Earth 10 The earth consists of air, water and land. THE ATMOSPHERE  We recognize these more technically as The atmosphere or gaseous portion of the earth the atmosphere, a gaseous envelope extends upward for hundreds of kilometers above the sea level. It is a mixture of nitrogen, oxygen, surrounding the earth; the hydrosphere, carbon dioxide, water vapour and other gases. the waters filling the depressions and covering almost three –quarters of the  The atmosphere makes life possible on our surface; planet. Moreover, it acts as an insulating agent protecting us from the heat and ultraviolet  the biosphere, which is all of the living or radiation of the sun and shielding us from once living materials on the earth. bombardment of meteorites, and it makes possible the evaporation and precipitation of  The geosphere or lithosphere, is the solid moisture. part of the earth which underlies the atmosphere and hydrosphere.  The atmosphere is an important geologic agent and is responsible for the processes of weathering which are continually at work on the earths’ surface.  THE HYDROSPHERE THE LITHOSPHERE  The hydrosphere includes all the waters  Of prime importance to the geologist is 11 the of the oceans, lakes and rivers on the lithosphere. surface of the earth, as well as ground water which exists in the pores and  This is , the solid portion of the earth, composed of crevices of the crustal rocks and soils. rocks and minerals which, in turn, comprised the Most of this water is contained in the continental masses and ocean basins. oceans, which cover 71% of the earths’ surface to an average depth of about  The rocks of the lithosphere are of three basic 4kms. types: igneous, sedimentary and metamorphic.  Igneous rocks were originally in a molten state,  The waters of the earth are essential to but have since cooled and solidified to form mans’ existence and they are also of rocks such as granite and basalt. considerable geologic importance.  Sedimentary rocks were formed from sediments Running streams and oceans are (fragments of pre-existing rocks deposited by actively engaged in eroding, transporting and depositing sediments; wind, water or ice. Limestone, sandstone and and water, working in conjunction with claystone etc are typical of this group. atmospheric agents, has been the  Metamorphic rocks have been transformed from major force in forming the earths’ rocks that were either sedimentary or igneous in surface features throughout geologic time. origin. This transformation takes place as the rock is subjected to great physical and chemical changes. Marble, which in its original form was limestone, is an example of a metamorphic rock.  BIOSPHERE THE PLANET EARTH-PHYSICAL DATA 12  The Earth is the third planet from the Sun, around This covers the sum total of all which it revolves in an elliptical orbit; one orbit organic life on the surface of the taking 365days, 5 hours, 48 minutes and 45.51 seconds. earth, in the oceans and the The maximum distance of the Earth from the sun atmosphere, and with which it  is 152.6 million km, and the minimum, 147.4 interacts to form the global million km. ecosystems. It sustains the evolution  The Earth rotates on its own axis, taking 23 hours, of todays’ life forms through the 56 minutes and 4.0996 seconds. geological time.  Its circumference at the equator is 40,076km, and at the poles 40,000 km.  Its mean mass is 5.997 x 1024 kg, and density 5517kg/cu.cm. It has a total surface area of 510,066,000 km2 of which the land surface is 148,950,800km2 (29.1%) and oceanic surface, 361,149,700 km2 (70.9%). The age of the Earth is estimated at about 4.6 billion years  The Earth in Space 13  The earth, its relation to the stars and  This galaxy (milky way) , which contains planets, and speculations as to its origin, every star that we can see with the naked attracted man’s curiosity long before the eye, is lens-shaped and contains birth of geological sciences. Although, such thousands of millions of stars, including studies fall more properly within the realm of our sun. astronomy, a brief survey of the earth and  A great mass of gaseous material, like the its planetary relations will provide the other star, the sun, has a diameter of reader with some understanding of its about 865,000 miles (1,392,082.56 km) and place in the universe. is located halfway between the centre  Galaxies, disc-shaped clusters containing and the edge of the Milky Way. The sun is millions or billions of stars, are the major important to man for it is the centre of the constituents of the universe. Astronomers solar system. The solar system is estimate that there are large numbers of composed of the sun, nine planets (all of galaxies in outer space. However, only one, which revolve around the sun), thousands the Milky Way, the galaxy in which the of asteroids or planetoids (small planets), earth is located, needs to be discussed. comets and meterors.  The planets, the largest of the solid  Located between the orbits of Mars and 14 bodies in the solar systems, all move on Jupiter are thousands of small planet-like essentially the same plane around the bodies called asteroids (or planetoids). sun. Nine (9) in number, they are (in They revolve around the sun in much the order from the sun): Mercury, Venus, same manner as the planets. Earth, Mars, Jupiter, Saturn, Uranus,  Meterors, rock-like objects travelling Neptune and Pluto. through space, become highly heated  Associated with most of the planets are when they enter the earths’ atmosphere. smaller bodies called satellites or These so-called ``shooting stars’’ are moons, which revolve around each usually completely burnt out before they planet. The moon, earths’ satellite, reach the earths’ surface. Some, revolves around our planet however, strike the earth as meteorites. approximately once every month. Some  The solar system also contains large self- planets (Mercury, Venus and Pluto) luminous, celestial bodies called comets. have no known satellites. However, When comets come near the sun, they Jupiter, the largest, has twelve. can be seen from the earth. Unfortunately, because of the eccentric ( off-center) orbits, comets are infrequently visible, but their return to the vicinity of the earth is mathematically predicted. 15  Internal structure of the Earth 16  The earths’ interior lies just below us, yet its accessibility to direct observation is very limited. Most of our knowledge of the interior of the earth comes from the study of Primary and Secondary waves that travel through the earth and emerge at some distant points. The technique involves accurately measuring the time required for seismic waves to travel from the focus of an earthquake or nuclear explosion to a seismographic station. On the basis of seismic investigation, the earth can be divided into 3 major zones i.e. the crust, mantle and core  17  CRUST: The outer superficial layer of the earth is called  At the bottom of the crust, earthquake waves the crust. It extends down to 30 to 40km beneath the continents and even further beneath some mountain undergo an abrupt increase in velocity as they regions and to about 10 km beneath sea level in enter a denser layer, the mantle. The crust- oceanic regions. The mean density of the continental mantle boundary is called Mohorovicic crust is between 2.37 and 3.30g/cm3 while that of the Discontinuity or shortened, the Moho. This is oceanic crust is about 2.9g/cm3. named after a Yugoslavian seismologist, Andrija  The materials making up the oceanic crust have been Mohorovicic, who did a pioneering study of called Sima, because they are rich in silicon, iron, and magnesium. The rocks are primarily of basaltic type. increase in seismic waves abruptly after 50km.  The material comprising the continental crust appears to  The crust that is intermediate in character occurs occur in two distinct layers. The upper layer is granitic or associated with the mobile belts. The thickness, granodioritic in nature. Because these rocks contain a high percentage of silicon and aluminum, they are often density and composition of this intermediate or referred to as Sial. The lower layer appears to be transitional crust can be highly varied due to the composed of simatic rocks, similar to those underlying complex ``mix’’ of continental and oceanic the oceanic basin. The upper sialic material resting on materials, with additions of various kinds of lower simatic rocks in the continental regions marks a boundary between the upper crust and lower crust and volcanism and intrusive. is referred to as Conrad Discontinuity.  MANTLE: The mantle has been divided into 18 2 layers, an upper mantle and lower  CORE: The core is the central part of the Earth, lying mantle; the boundary between these below the Gutenberg discontinuity. The core normally being taken at 1000km depth. extends from a depth of about 2900km to the Most recent studies suggest a depth of centre of the earth. It comprises about 16% of the earths’ volume and 31% of its mass. about 700km to be more appropriate.  The core is divided into a liquid outer core and a  The mantle is solid and at about 2900km, is solid inner core. S-waves do not pass through the a boundary with the third major layer, the outer core, indicating that the outer core is liquid in nature. Core. Although the thickness of the mantle is less than half the earths’ radius, the  The mantle-core boundary is called Gutenberg Discontinuity. At this boundary, the density mantle forms 83% of the total volume of increases from 5.5g/cm3 to 10.0g/cm3. The the earth and about 68% by mass. The Gutenberg discontinuity is marked by reduction of mantle is thought to be ultrabasic in P-waves and the disappearance of S-waves. It probably reflects a change in composition from composition i.e. very low in silica and solid phase of the mantle to liquid phase of the correspondingly rich in magnesium and core. It has been suggested that the core is mainly iron. The mantle is assumed to give rise to iron and some nickel and that both liquid outer core and the solid inner core are made up of the crust. nearly the same materials. The inner core is about 1220km thick, with temperatures in the region of 6650oC. Lighter materials (perhaps sulfur, oxygen or silicon) may also be present in small amounts (perhaps 8-20%) to explain its density. See you in the physical class! 19