Chapter I - Introduction to Geology and the Components of the Earth System 2024/2025 PDF

Chapter I: Introduction to Geology and the Components of the Earth System 2024/2025 1. What is Geology? Geology (in Greek, Geo means Earth, Logos means Science) is a branch of science dealing with the study of the Earth. It is also known as earth science. The study of the earth comprises of th...

Chapter I: Introduction to Geology and the Components of the Earth System 2024/2025 1. What is Geology? Geology (in Greek, Geo means Earth, Logos means Science) is a branch of science dealing with the study of the Earth. It is also known as earth science. The study of the earth comprises of the whole earth, its origin, structure, composition and history (including the development of life) and the nature of the processes. 2. Main Branches of Geology Being a broad and diverse field, Geology has many branches and applications. Further, let’s take a look at the four major branches of Geology along with some examples, namely: physical geology, historical geology, environmental geology, and economic geology. 2.1 Physical Geology Physical geology is the branch of geology that studies the physical features and processes of the Earth. It investigates how the Earth’s surface and interior are shaped by natural forces such as plate tectonics, erosion, weathering, volcanism, earthquakes, etc. Physical geology also examines the properties and classification of earth materials such as minerals and rocks. Some examples of physical geology topics are:  Geomorphology: the study of landforms and their formation.  Mineralogy: the study of minerals and their structure, composition, identification, and classification.  Petrology: the study of rocks and their origin, composition, texture, and classification.  Volcanology: the study of volcanoes and volcanic phenomena.  Seismology: the study of earthquakes and seismic waves. 1 Chapter I: Introduction to Geology and the Components of the Earth System 2024/2025 2.2 Historical Geology Historical geology is the branch of geology that studies the geological history of the Earth and its life forms. Additionally, it reconstructs the past events and changes that have occurred on the Earth’s surface and interior over billions of years. Historical geology also explores the origin, evolution, extinction, and distribution of life on Earth. Some examples of historical geology topics are:  Stratigraphy: the study of rock layers (strata) and their correlation, dating, and interpretation.  Paleontology: the study of fossils and ancient life forms.  Geochronology: the study of the age of rocks and geological events using various dating methods such as radiometric dating. 2.3 Environmental Geology Environmental geology is the branch of geology that studies the interactions between the Earth and human activities. It evaluates how human activities affect or are affected by the Earth’s systems such as the atmosphere, hydrosphere, biosphere, and lithosphere. Some examples of environmental geology topics are:  Hydrogeology: the study of groundwater flow, quality, quantity, and management.  Geochemistry: the study of chemical composition and reactions of earth materials and fluids.  Engineering geology: the study of geological factors that influence engineering projects such as dams, bridges, tunnels, buildings, etc. 2 Chapter I: Introduction to Geology and the Components of the Earth System 2024/2025 2.4 Economic geology Economic geology is the branch of geology that studies the earth’s materials that have economic value or potential. It investigates the occurrence, distribution, extraction, and utilization of mineral and energy resources such as metals, gemstones, coal, oil, gas, etc. Some examples of economic geology topics are:  Mining geology: the study of ore deposits and their exploration, mining, processing, and reclamation.  Petroleum geology: the study of oil and gas deposits and their exploration, drilling, production, and transportation.  Mineral economics: the study of supply, demand, price, and trade of mineral resources. 3. Importance of geology to man Geology is important because virtually all the natural materials our society needs such as oil, gas, metals, building materials, and so forth are found by geologists. Geologic engineers evaluate roads, buildings and dams for geologic stability and hazard potential. The entire human race depends directly or indirectly on geology for its livelihood and survival, for example; the cloths you wear, the radio you listen to, the food you eat and even the pencil you use at school exist because of geologic discoveries. Let us elaborate on the geology surrounding the pencil;  Pencil brass : from copper or zinc  Wood : shaped by machines made of iron  Colour : paint pigment from various minerals  Pencil lead : from lead, graphite and clays 3 Chapter I: Introduction to Geology and the Components of the Earth System 2024/2025 Figure 01: Relationship between geology and other science subjects 4 Chapter I: Introduction to Geology and the Components of the Earth System 2024/2025 4. Solar system: Assemblage consisting of the Sun and those bodies orbiting around it: 8 planets with about 210 known planetary satellites (moons); countless asteroids ; comets and othericy bodies; and vast reaches of highly tenuous gas and dust. Located at the center of the solar system and influencing the motion of all the other bodies through its gravitational force is the Sun, which in itself contains more than 99 percent of the mass of the system. Visualized from Figure 02, all the eight planets are observed to move around the Sun counter-clockwise in an elliptical orbit. Figure 02: The Solar system. 5 Chapter I: Introduction to Geology and the Components of the Earth System 2024/2025 4.1 Planets category: As two categories of planets are “The Giant Planets” and “The Terrestrial Planets”: a) The Terrestrial Planets: the sizes of the planets of “The Terrestrial Planets” category are generally small in size. Those planets are Mercury, Venus, the Earth, and Mars. They are mainly rocky in nature or composition. b) The Giant Planets: On the other side, “The Giant Planets” i.e. Jupiter, Saturn, Uranus, and Neptune; are very giant in size. They are the largest planets in the solar system. They contain a high range of “hydrogen ices and gases”. Figure 03: Planets category 6 Chapter I: Introduction to Geology and the Components of the Earth System 2024/2025 5. The Earth Earth is the fifth largest planet in the solar system; it is the only world in our solar system with liquid water on the surface. Just slightly larger than nearby Venus, Earth is the biggest of the four planets closest to the Sun, all of which are made of rock and metal. When the solar system settled into its current layout about 4.5 billion years ago, Earth formed when gravity pulled swirling gas and dust in to become the third planet from the Sun. Like its fellow terrestrial planets, Earth has a central core, a rocky mantle, and a solid crust. 5.1 The Composition and Structure of Earth The Earth can be divided into layers based on chemical composition and physical characteristics. Figure 04: Layers of the Earth (Noreen Meghani 2016) 7 Chapter I: Introduction to Geology and the Components of the Earth System 2024/2025 5.1.1 Compositional Layers (chemical composition) The Earth has different compositional and mechanical layers. Compositional layers are determined by their components, while mechanical layers are determined by their physical properties. a- Crust This is the layers on which you stand on. All the mountain, jungles and oceans you know are carried on this layer. It is the thinnest layer of the four layers. This layer is 70 Km thick on the land, and 5 Km thick at some ocean floors. The crust is mostly composed of silica, alumina, lime, magnesia, and iron oxide (rust). b- Mantle This layer starts below the crust layer, and is denser than the crust. It is 3,000 Km in thickness. It is mostly made of silicate rocks rich in magnesium and iron. This layer is not a perfectly solid. At some locations, the rock is completely melted, which is called magma. When this magma reaches near the crust, it erupts as Lava from the volcanoes. c- Core The innermost layers of the Earth. The Earth has an outer core (liquid) and an inner core (solid). They are not chemically distinct from each other, but they are chemically distinct from the mantle. The core is mainly composed of nickel and iron. Its depth is 2900-6370km. 8 Chapter I: Introduction to Geology and the Components of the Earth System 2024/2025 Figure 05: compositional and Mechanical layers of the Earth 5.1.2 Mechanical Layers (physical characteristics) The mechanical layers of the Earth a differentiated by their strength or rigidity. These layers are not the same as the compositional layers of the Earth, such as the crust, mantle, and core, though sometimes the boundaries fall in the same places. Based on physical properties internal structure of the Earth is divided into : (1) Lithosphere, (2) Asthenosphere, (3) Mesosphere, (4) Outer Core and (5) Inner Core. a- Lithosphere Lithosphere (“rock sphere”) includes the crust and part of the upper mantle. It is solid, strong, and rigid outer layer of a planet. Earth’s lithosphere varies greatly in thickness, from as little as 10 km in some oceanic areas to as much as 300 km in some continental areas. 9 Chapter I: Introduction to Geology and the Components of the Earth System 2024/2025 Figure 06: Earth’s Lithosphere. b- Asthenosphere Asthenosphere (astheno means weak) is the upper portion of the mantle. It is present just below the lithosphere ranging up to 80-200 km. Density of asthenosphere is higher than that of the crust. It is ductile, and mechanically weak. These characteristics of the asthenosphere help in the movement of plate tectonic and isostatic modifications (the elevated part at one part of the crust area is balanced by a depressed part at another crust area). Asthenosphere is the main source of magma that reaches to the surface during volcanic eruptions. Figure 07: Earth’s Asthenosphere. 10 Chapter I: Introduction to Geology and the Components of the Earth System 2024/2025 c- Mesosphere Mesosphere (“middle sphere”) is the region between the asthenosphere and the core. The rock below the asthenosphere is stronger and more rigid than in the asthenosphere. It is so because the high pressure at this depth offsets the effect of high temperature, forcing the rock to be stronger than the overlying asthenosphere. d- Outer Core A layer of liquid iron and nickel (and other elements) beneath the mesosphere. This is the only layer of the Earth that is a true liquid, and the core-mantle boundary is the only boundary of Earth’s layers that is both mechanical and compositional. Flow of the liquid outer core is responsible for Earth’s magnetic field. e- Inner Core: The innermost part of Earth is the core and is about 2414 km thick. Both the inner and outer cores consist primarily of iron and nickel. They're extremely hot, with temperatures ranging from 7200–9000℉ (4000–5000℃). 11 Chapter I: Introduction to Geology and the Components of the Earth System 2024/2025 Figure 08: The Structure of the Earth 12