Geology a science that examines the earth, its form and composition, and the changes it has undergone and is undergoing involves the knowledge of what happened before and the events occurring within the atmosphere requires not only a study of the materials found on earth but an understanding of the various geologic processes aims to develop an understanding of the earth’s materials and how these materials were changed and modified through the action of natural forces over a period of time Geology as a Discipline Two areas of Geology: Physical Geology – deals with the study of the materials composing the earth nd the processes and phenomena that operate beneath and upon its surface.
Historical Geology – deals with the study of the evolution of the earth. Physical geology precedes historical geology because we need to know how our own planet works before we attempt to open its past.
Astronomical Studies About the Earth Aristotle the first to suggest heliocentric universe but was rejected Aristarchus the first Greek to advocate a sun-centered universe (heliocentric) Pythagoras suggested that earth rotates upon an axis and revolves around the sun in its orbit also advocated heliocentric theory Cladius Ptolemy dvanced the geocentric theory which describes the individual apparent path that the sun, moon, planets, and stars follow while moving around a stationary earth Nicolaus Copernicus emerged and revived the first great heliocentric Tycho Brahe responsible for building pointers used to measure the location of heavenly bodies.
Galileo Galilei invented the first astronomical telescope used to support the Heliocentric Theory Johannes Kepler discovered the three fundamental laws of planetary motion which describes the Copernican Theory Sir Isaac Newton Discovered the laws of gravitation and motion that makes Kepler’s and Copernicus’ explanation be understood. Age of the Earth The earth and meteorites were formed from the same materials (solar nebula) and presumably at the same time. Due to this, the earth is inferred to have formed at about 4. 55 billion years ago.
The oldest terrestrial rocks that have been accurately dated directly are close to 4 billion years old and the oldest rocks on each continent are found to be generally between 3. 6 and 3. 9 billion years old. Size of the Earth Erastosthenes calculated the size of the earth by measuring the distance between a deep well to Syene and Alexandria and the angle of the moon and un in Alexandria on the first day of summer. Through mathematical calculation, he found the angle of the moon and sun to be a little more than 70 which is almost 1150th of the complete circle. Before, it was believed that the earth was perfectly round. However, Isaac Newton proved that the earth’s circumference at the poles was less than the circumference at the equator. Its diameter at the equator is about 43. 2 greater than diameter at the poles.
Scientists agree that the slight bulge is caused by rapid rotation of the earth on its axis which makes the earth’s shape spherical. Shape of the Earth The degree of latitude is longer at the vicinity of the poles than near the equator. Analysis shows that the resulting shape of the earth is an oblate spheroid. This means that the earth is flat at the poles while the the equitorial regions are slightly bulging hence a person at one end of the poles would be nearer the earth’s center than he would be at the equator. The earth’s oblate shape and its rotation reduce the weight of an object at the equator than its weight at the poles. The equatorial bulge also produces slight disturbances on the motions of the moon and artificial satellites. Proofs of the Shape of the
Earth 1) Several planes made to go around the largest circumference of the earth, each starting in a different direction, showed that all flights were of equal distances. 2) Persons aboard a ship observe that a passing ship receding farther and farther into the distance seems to sink gradually beneath the water level. 3) Observations made during a lunar eclipse reveal that the earth’s shadow cast on the moon appears circular. 4) Photographs of the earth taken at very high altitude show the horizon as a curves line. 5) An observer at the equator sees the North Star on the horizon but as he travels oward the North pole, the star appears higher and higher in the sky until it is directly overhead at the North Pole. 6) It is found in surveying operations with precise telescopic instruments.
His level of sight would be horizontal perfect according to the level bubble on the telescope. 7) Objects weigh the same every”here because all points on the earth’s surface are equidistant from the center. However, the earth’s shape is not perfect as shown by a slight variation in gravity. 8) Modern navigation methods are based on the assumption that the earth is a sphere since position of vessels have been etermined for centuries by these methods, it follows therefore that the correctness of the assumption has been fully established. Motions of the Day and Night Structures and Composition of the Earth 30% of earth’s crust is covered by land and the rest id covered up with water.
Land Surface The big masses of land are known as continents while the small ones are called islands. The land areas are characterized by such features as plains, mountains, hills, and plateaus. Covering the land features in most places is a layer of loose materials composed of soil, sand, rock, large boulders, gravel, and clay. Water Surface Ocean floor has an average depth of 3,800 meters. Marianas Trench is 1 1 ,034 meters deep. Structures of the Earth Effects of Earth’s Revolution Maps and Map Reading Map – a systematic representation of all or a part of the earth on a flat surface (plane). Atlas – a bound collection of maps and charts. Globe – a ball (shpere) with the representation of the earth on its surface.
Importance of Maps Means by which the earth’s surface can be brought into the laboratory and studied. Means of gaining knowledge and understanding of the earth’s structure and the forces working constantly to change the surface features. Gives a clear evidence of the past events that have shaped the region. Most effective means for showing the location of both natural and cultural features, their sizes and their relationships to one another. Readily displays information that would be impractical to express in words. Basic Features of Maps Grid – means the network of the lines of latitudes and longitudes used on maps and globes. Latitudes – extends east to west on the globe and measure distances north and south from the equator to the poles.
Longitudes/ Meridians – extend from pole to pole in a north-south direction and are used o measure distances east up to 1800 and west to 1800 from prime meridian. Scale – expresses the relationship between distance or area on the map to the distance or area of the earth’s surface. This is usually expressed as ratio or fraction. Color and Symbol ” each color and symbol used on maps has an importance Red – urban areas, important roads, public land, subdivision lines Blue – water features Black – construction work, green woodlands, orchards, etc. Basic Symbols in Topographic Map Latitude and Longitude Types of Maps Topographic Maps show landforms Includes all details that make up the surface features of the land Political
Show national and local boundaries Show relative sizes of town and cities and their political importance Navigation Maps Show routes and distances Hydrographic Maps Show depth of water and the topography of the ocean floor Relief Map Small model of the land surface Used in classrooms to give students an idea about the irregularities of the land Weather Map Show weather phenomena for a particular period Geologic Map Show the distribution of rock formations Key Concepts The Age of the earth is said to be not more than 10 billion years and not less than 4. 6 billion years The earth makes one complete rotation in 24 hours. It takes earth 365 “‘4 days to travel once around its orbit. This is called a solar year. 30% of the earth’s crust is covered by land and the rest is covered by water. Map is one basic tools to be used in the study of the earth.
The basic features are grid, scale, color, symbols, and lines of latitude, longitude, meridians. Time is the basic concept that deals with the occurrence of events. It can be measured in terms of year, month, week, day, hour, minute, or second. The tropical year is measured by the time the earth takes to make one revolution around the sun. Equinox is the time of the year of equal lengths of days and nights. GeologicalForce thatshapes theearth Diastrophism It is the Dynamical forces generally tend to elevate the earth’s surface. They are in constant battle against external forces that tend to wear away the land surface. Theories of Diastrophism 1 . Theory of Isostacy- From Greek word meaning “equal standing”.
It states that as rocks from higher region is removed by erosion and deposited on a lower region slowly rises while the lower region becomes heavier and slowly sinks. 2. Contraction Theory- It states that the earth is gradually shrinking. As the Shrinkage , occurs, the stronger and the heavier blocks of the blocks sinks. . Convection Theory- A Theory which would account for the pushing and folding of rocks through convection currents Continental drift theory Is the theory which accounts for diastrophic movement and for the folding and faulting along the edges of the continents. *CONSTRUCTION THEORY EXPANSION THEORY Is a theory which states that the earth is gradually expanding. Expansion of the earth world change the continents’ positions.
STRUCTURALFEATURES OF EARTH MOVEMENT DEFORMATION OF ROCKS -the effects of diastrophism is more clearly seen in rocks, especially in sedimentary rocks . Any deformation of sedimentary rocks n shown in tilts , bends , or break in the layer FOLDS- A bend or flexure in a rocks that can be likened to waves in the ocean . Each has a crust or uphold and a trough or down fold . DIP AND SRIKES- Dip is the angle between the horizontal plane and a structural surface . PITCHING FOLDS- Folds whose axes slant downward at each end of an imaginary line running along the top of an a anticline or along the bottom ofa syncline are called the axis of he folds the angle between the axis and the horizontal is called pitch.
JOINTS AND FISSURES A joints is a fractures or a little separation between the rocks walls while issures are cracks or actual gaps between the rocks walls . FAULTING- It refers to the surface along which a rock body has been broken and has been displaced. Types of fault 1 . Thrust fault- A low angle fault (45 degrees or less) in which the hanging wall is moved upward in relation to the footwall. 2. Normal fault- also called gravity fault, a dip-slip fault in which the hanging wall moves downward relative to the footwall. 2. Reverse fault- is the material above the fault plane that moves up in relation to the material below. It shows the surface area Of the crust. Earthquakes
An Earthquake is a ground displacement associated with the sudden release in the for of seismic waves, of build-up stress in the lithosphere. Seismic waves- Sounds waves traveling through and across the earth that are produce by earthquake. Three major types of Seismic Waves 1. Primary wave- These are kind of longitudinal wave, identical in character to sound wave passing through a liquid or gas. 2. Shear wave or a secondary wave- In this type, particles oscillate back and fourth at right angle to the direction of the wave travel. 3. Surface waves- Those are seismic waves that travel along the outer layer of the earth. Effects of Earthquake . Soil Reaction- In severe quakes, shaking of the ground can loosen soil and rocks and precipitate disastrous landslides.
Seiches Standing bodies of water an reservoirs, sometimes experience what are called seismic seiches. Seismic sea waves or Tsunami A rapidly moving ocean wave generated by earthquake activity is capable of inflicting heavy damage in coastal regions. MOUNTAINS The mountain belt means a long linear zone in the earth’s crust where the rocks have been intensely deformed by horizontal stresses and generally intruded by molten rock material. The topography can be high and ugged, or it can be worn down to a surface of low relief. Most people think of a mountain as simply a high, or more or less rugged land form, In contrast to flat and low land. Orogenesis- The process of mountain building is called orogenesis.
The factors appear to be most important in this process are: Rock Sequence 1 . Geosynclinal sedimetation and contemporaneous subsidence. 2. Compression and deformation 3. Uplift and erosion Structural deformation This deformed structure compression, in which the scale of deformation ranges from wrinkle grains Of fossils in the rocks to folds tens Of kilometer ide. Metamorphism This refers to changes in the mineral composition and texture of rocks subjected to high temperature and pressure within the earth. Igneous activity This is the concentration of the earth’s lighter lighter mterial in the continental crust which takes place in two steps.
General Classification of Mountains Mountains may be classified either 1 . Geographically and chronologically. according to their arrangement or 2. Structurally, according to their to their geological stratification. Kinds of Mountains 1. Folded mountains or complex mountains- This result from folding of edimentary or lava Beds or may result from variable resistance to erosion. 2. Volcanic Mountains These result from the accumulation of lava and pyroclastics of volcanic events. 3. Erosion Volcanic Mountains These are single mountains or a group of mountains that have been formed by the erosion Of Streams. 3. Fault-block mountains 4. These are mountains that are formed by the displacement of a rock along fault. 5.
Upwarped-mountains These are produced in association with a broad arching of the crust or In some instances because of vertical displacement along high angle faults. Plateaus Is an extensive upland region. It is also often referred to as table land, since it is essentially flat-topped and stands conspicuously above an adjacent land area. Weathering, Erosion and Soil WEATHERING is the interaction between the elements in the atmosphere and the rocks exposed at the earth’s surface. The relative importance of different kinds of weathering processes is largely determined by climate.
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