Physical Geology (GEOL 201) Introduction PDF

A The Formation of the Solar Physical Geology (GEO...

A The Formation of the Solar Physical Geology (GEOL 201) System B Introduction C Dr. Mohamed Salah Department of Earth Sciences D Faculty of Arts and Sciences American University of Beirut (AUB) Email: [email protected] The Earth System 1 E 2 6/10/2024 6/10/2024 Chemical element, Crystals, Mineral Minerals are the basic constituents of rocks! Stone. Pumicite. Conglomerate. Rocks tell us many things! 6/10/2024 6/10/2024 Introduction 3 6/10/2024 Introduction 4 1  Ocean vs. Continents: Why do they exist? How did they form? Rocks, layers of rocks, sediments! Geology is an outdoor Science! Oceans cover 71% of the Earth’s surface! 6/10/2024 Introduction 5 6/10/2024 Introduction 6 Late Paleozoic (260 Ma) Earth changes, continents and oceans are in a continuous motion. Land and ocean distribution has been always changing Cretaceous (100 Ma) throughout geological times. Time Eocene (40 Ma) Is this geographic distribution of landmasses/oceans fixed? 8 6/10/2024 Introduction 6/10/2024 Introduction 7 2  Earthquakes and Volcanoes: Why are some regions subjected to frequent earthquakes and active volcanoes whereas others not? 1. Distribution of earthquakes around the Pacific Ocean: The Circum-Pacific Belt! 1. The Circum-Pacific Belt! 2. Concentration of volcanoes around the Pacific 2. The Mediterranean-Alpian-Himalayan Belt Ocean: The Ring of Fire! The Earth System 6/10/2024 6/10/2024 Introduction Introduction 10 GEOLOGICAL HAZARDS! We are subjected to the Earth dynamics. Earthquakes are caused by the breaking of rocks along geologic faults! CO2 emissions - Global Warming Offshore earthquakes The burning of fossil fuels is the main may cause tsunamis. The 2011 tsunami that cause of global warming and many struck Japan. subsequent catastrophic consequences! 1906 2004 Carroll Glacier, Alaska 11 6/10/2024 Introduction 6/10/2024 Introduction 11 12 3  Mountains. How did the Shrinking glaciers: Himalaya, Alps, and the Rocky The burning of fossil fuels to power the modern society causes Global mountains rise to such great Warming and many other catastrophic consequences! heights? Introduction 6/10/2024 Mount Everest is 8.8 km asl. 14 6/10/2024 13 Oil (liquid petroleum) Resources from marine geology are everywhere in our daily life! Meteorite. Extinctions. New life! The Earth is a fragile planet. What changes are likely to occur in 6/10/2024 the future? 15 6/10/2024 15 4  The goal of geology—and of science in general—is to explain the 1) The Scientific Method physical universe. Scientists believe that physical events have physical explanations, The Earth is a unique planet........ Why? even if they may be beyond our present capacity to understand them. Geology is the science that studies Earth: How was it born? How did it evolve? How does it work?, and How can we The scientific method, on which all scientists rely, is the general procedure for discovering how the universe works through preserve its habitats for life? systematic observations and experiments. The term geology (from the Greek words for “Earth” and “knowledge”) was coined by scientific philosophers more than 200 Using the scientific method to years ago to describe the study of rock formations and fossils. make new discoveries and to Through careful observations and reasoning, their successors confirm old ones is the process of developed the theories of biological evolution, continental drift, and scientific research. plate tectonics—many of which are major topics of this course. These geologists are researching soil samples near a lake in Minnesota. 6/10/2024 The Earth System 20 6/10/2024 The Earth System 21 When scientists propose a hypothesis—a tentative explanation based on data collected through observations and experiments— A coherent set of hypotheses that explains some aspect of they present it to the community of scientists for criticism and nature constitutes a theory. repeated testing. Theories usually obey physical laws -general principles about how A hypothesis is supported if it explains new data or predicts the the universe works that can be applied in almost every situation, outcome of new experiments. A hypothesis that is confirmed by such as Newton’s law of gravity. other scientists gains credibility. Some hypotheses and theories have been so extensively tested Here are four interesting scientific hypotheses that we will that all scientists accept them as true. encounter in this course: For instance, the theory that Earth is nearly spherical is supported by so much experience and direct evidence that we take it to be a fact. 1. Earth is billions of years old. 2. Coal is a rock formed from dead plants. The longer a theory holds up to all scientific challenges, the more 3. Earthquakes are caused by the breaking of rocks along geologic confidently it is held. faults. 4. The burning of fossil fuels causes global warming. 6/10/2024 The Earth System 22 6/10/2024 The Earth System 23 5  2) Geology as a Science A scientific model: Knowledge based on many hypotheses and theories can be used to create a scientific model—a precise The major questions of geology involve processes that representation of how a natural process operates or how a operate on larger and longer scales. natural system behaves. Controlled laboratory measurements yield critical data for Scientists combine related ideas in a model to test the consistency of testing geologic hypotheses and theories—the ages and their knowledge and to make predictions. properties of rocks, for instance—but they are usually Like a good hypothesis or theory, a good model makes predictions that insufficient to solve major geologic problems. agree with observations. To encourage discussion of their ideas, scientists share those ideas and The great discoveries about the Earth were made by the data on which they are based. They present their findings at observing Earth processes in their uncontrolled, natural professional meetings, publish them in professional journals, and explain environment. them in informal conversations with colleagues. Scientists learn from one another’s work as well as from the discoveries For this reason, geology is an outdoor science with its own of the past. particular style and outlook. Geologists go to the field to observe nature directly. 6/10/2024 The Earth System 24 6/10/2024 The Earth System 25 Geology is principally an outdoor science. Here, a geologist welds a GPS station placed on the flanks of Mount St. Helens. The stations will monitor the Geologists discover how ocean basins have evolved by sailing rough seas to changing shape of the land surface as molten rock moves upward within the map the ocean floor. Here, the research crew lowers a corer that will gather volcano. mud and sediment from the ocean floor. 6/10/2024 The Earth System 26 6/10/2024 The Earth System 27 6 ▪ Geology is closely related to other areas of Earth science, including: 1. Oceanography, the study of the oceans. 2. Meteorology, the study of the atmosphere. 3. Ecology, the study of the abundance and distribution of life. ▪ Geophysics, geochemistry, and geobiology (paleontology) are subfields of geology that apply the methods of physics, chemistry, and biology to geologic problems. Geophysicists deploy instruments A geochemist readies a rock Geobiologists investigate to measure the underground sample for analysis by a mass underground life inside Spider activity of a volcano. spectrometer. Cave at Carlsbad Caverns, New Mexico. 6/10/2024 The Earth System 28 6/10/2024 The Earth System 29 A special aspect of geology is its ability to probe Earth’s long history by reading Geology is a planetary science that what has been “written in stone.” uses remote sensing devices, such The geologic record is the information as instruments mounted on Earth- preserved in the rocks that have been orbiting spacecraft, to scan the formed at various times throughout the entire globe. Earth’s history. Geologists develop computer models Geologists decipher the geologic record that can analyze the huge quantities by combining information from many of data amassed by satellites to kinds of work: examination of rocks in map the continents, chart the the field; careful mapping of their positions relative to older and younger motions of the atmosphere and rock formations; collection of oceans, and monitor how our representative samples; and environment is changing. determination of their ages using An astronaut checks out sensitive laboratory instruments; etc. instrumentation for monitoring Earth’s surface. These multicolored layers of sand at Colorado National Monument were deposited more than 200 million years ago. 6/10/2024 The Earth System 30 6/10/2024 31 7  The geologic record tells us that the processes we see in action on Earth today have worked in much the same way throughout the geologic Geologists (Earth Scientists) seek answers to many basic past. questions: This important concept is known as the principle of uniformitarianism. This 1. Of what material is the planet composed? concept was later summarized in a memorable line: “The present is the key to the past.” 2. Why are there continents and oceans? 3. How did the Himalayan, Alps, and Rocky Mountains rise to their Geologic 1 2 great heights? processes take 4. Why are some regions subject to earthquakes and volcanic place over a eruptions while others are not? tremendous 5. How did Earth’s surface environment and the life it hosts range of scales evolve over billions of years? in both space and time: 6. What changes are likely to occur in the future? 1. Some take place over thousands of The answers to such questions are fascinating. centuries! 2. Others occur rapidly! Welcome to physical geology! 6/10/2024 Introduction 6/10/2024 The Earth System 32 33 Physical Geology 3) Earth’s Shape and Surface Physical geology: A scientific discipline of geology that is concerned with Earth is not a perfect sphere. Because of its daily rotation, it all aspects of the Earth: its formation, structure, composition, physical bulges out slightly at its equator and is slightly squashed at its properties, constituent minerals and rocks, different Earth processes, and poles. surficial features. The smooth curvature of the Earth’s surface is broken by mountains and valleys and many other ups and downs. Earth’s topography is measured with respect to sea level, a smooth surface set at the average level of the ocean water. Earth’s topography is measured with respect to sea level. 6/10/2024 Introduction 34 6/10/2024 The Earth System 35 8  4) Peeling the Onion: Discovery Earth’s Density of a Layered Earth The density of a substance is its mass divided by volume. The Earth’s average density is about 5.5 g/cm3; twice that of tombstone Seismic waves, generated granite. by earthquakes, when recorded by sensitive Some iron-rich rocks brought to Earth’s surface by volcanoes have instruments called densities as high as 3.5 g/cm3. seismometers, allow Going downward into Earth’s interior, the pressure on rock increases geologists to locate with the weight of the overlying mass. The pressure squeezes the earthquakes and to make rocks into smaller volumes, making density higher. pictures of Earth’s inner workings. The Mantle and Core Earth’s interior is divided In thinking about what lay beneath our feet, scientists turned to into concentric layers of meteorites, which are pieces of the solar system that have fallen to different compositions, Earth. separated by sharp, nearly Meteorites may be made of an alloy of two heavy metals, iron and spherical boundaries. nickel, and thus may have densities as high as 8.0 g/cm3. 6/10/2024 The Earth System 36 6/10/2024 The Earth System 37 These two elements (Fe and Ni) are relatively abundant throughout The Crust our solar system. Two common types of meteorites are shown below. The Moho boundary separates the crust composed of low-density Sometime in Earth’s past, most of the iron and nickel in its interior silicates from the higher-density silicates of the mantle, which contain had dropped inward to its center under the force of gravity. This more magnesium and iron. movement created a dense core, which is surrounded by a shell of The Moho is shallower beneath the oceans than beneath the continents. less-dense, silicate-rich, rock that is called the mantle. On average, the thickness of the oceanic crust is only about 7 km, compared to almost 40 km for the continental crust. 1. This stony meteorite, which is similar in 2. This iron-nickel meteorite, which is composition to Earth’s silicate mantle, has similar in composition to Earth’s core, a density of about 3.0 g/cm3. has a density of about 8.0 g/cm3. 6/10/2024 The Earth System 38 6/10/2024 The Earth System 39 9  The Inner Core 5) Earth as a System of This is another sharp spherical boundary at the much greater depth of 5150 Interacting Components km, indicating a central mass with a higher density than the liquid outer core. The inner core transmits both shear and compressional waves. The inner core Earth is a restless planet, continously changing through geologic is therefore a solid metallic sphere suspended within the liquid outer core. The activities such as earthquakes, volcanoes, and glaciation. These radius of the inner core is 1220 km, about two-thirds of the Moon’s radius. activities are powered by two heat engines: one internal, the other external. Jumps in density between Earth’s major layers are caused primarily by differences in their chemical composition. All parts of our Iron and oxygen are the most abundant planet and all elements, but they are distributed their differently: The The The interactions, Iron, the densest, is concentrated in the Mantle Liquid Solid taken together, core, whereas oxygen, the least dense, is Outer Inner constitute the Core Core concentrated in the crust and mantle. Earth system. The crust contains more silica than the mantle, and the core almost none. 6/10/2024 The Earth System 40 6/10/2024 The Earth System 41 Gear of Earth science concepts: Earth’s internal heat engine is powered by the heat energy trapped in The Earth as a system of interacting components: its deep interior during its violent origin and released inside the planet by radioactivity. This internal heat drives movement in the mantle and core, supplying the energy that melts rock, moves continents, and lifts up mountains. Earth’s external heat engine is driven by solar energy: heat supplied to Earth’s surface by the Sun. The external heat engine energizes the atmosphere and oceans and is responsible for Earth’s climate and weather. Rain, wind, and ice erode mountains and shape the landscape, and the shape of the landscape, in turn, influences the climate. The Earth System 6/10/2024 The Earth System 42 6/10/2024 43 10  Specialized Two main systems control Earth processes: subsystems that produce specific 1. The climate system includes all the Earth system components types of activity, that determine climate on a global scale and how climate such as climate changes with time. change or mountain 2. The Plate Tectonic System: Earth’s most dramatic geologic building, are events—volcanic eruptions and earthquakes, for example— called result from interactions within Earth’s interior. These geosystems. phenomena are driven by Earth’s internal heat, which is The Earth transferred upward through the circulation of material in the system can be Earth’s mantle. thought of as a collection of This general many open, process, in which interacting (and hotter material rises often and cooler material overlapping) sinks, is called geosystems. convection. The Earth system encompasses all parts of our planet and their interactions. 6/10/2024 44 6/10/2024 45 The magnetic field produced by the geodynamo -the swirling currents in the Earth’s outer core- reaches outward Interactions Among Geosystems Support Life into space far beyond Earth’s atmosphere. The biosphere—the habitat of life—participates as an active There, it forms a barrier to the highly energetic particles that component of the climate system, regulating the amount of CO2, stream outward from the Sun—the solar wind. CH4, and other greenhouse gases in the atmosphere, which in turn determines the planet’s surface temperature. Without this shield, Plate tectonics produces volcanoes that resupply the Earth’s surface would atmosphere and oceans with water and gases from Earth’s deep be bombarded by harmful solar radiation, interior, and it is responsible for the tectonic processes that which would kill many raise mountains. forms of life that now The interactions of the atmosphere, hydrosphere, and prosper in its biosphere. cryosphere (ice-covered areas) with the surface topography create a variety of habitats that enrich the biosphere and, through the erosion of rock and dissolution of minerals, provide life with essential nutrients. The Earth System The Earth System 6/10/2024 46 6/10/2024 47 11  6) An Overview of Geologic Time Geologists look into the “deep time” of Earth’s early history (measured in billions of years), just as astronomers look into the Using evidence from meteorites, geologists showed that the “deep space” of the outer universe (measured in billions of light- Earth and the other planets of the solar system formed years). about 4.56 billion years ago through the rapid condensation of a dust cloud that circulated around the young Sun. Life also began very early in Earth’s history, as we can tell from the study of fossils, traces of organisms preserved in the geologic record. Fossils of primitive bacteria have been found in rocks dated at 3.5 billion years ago. A key event in Earth’s history was the evolution of organisms that release oxygen into the atmosphere and oceans. This geologic time line shows some of the major events observed in the geologic record, beginning with the formation of the planets. The Earth System 6/10/2024 48 6/10/2024 The Earth System 49 Five of these huge turnovers are marked on the geologic time line below. Life on early Earth was simple, consisting mostly of small, The most recent one was caused by a large meteorite impact 65 million single-celled organisms that floated near the surface of the years ago. The meteorite caused the extinction of half of Earth’s species, including all the dinosaurs. oceans or lived on the seafloor. In addition to meteorite impacts, scientists have proposed Between 1 and 2 billion years ago, more complex life-forms such as algae other kinds of extreme events, such as rapid climate changes and seaweeds evolved. brought on by glaciations and massive eruptions of volcanic Although biological evolution is often viewed as a very slow material. process, it is punctuated by brief periods of rapid change. Spectacular examples are mass extinctions, during which many kinds of organisms suddenly disappeared from the geologic record. 6/10/2024 The Earth System 50 6/10/2024 The Earth System 51 12  In a geologic sense Humans are quite a new “addition” to the Earth system; however, their impact has been very large. Geologic Time Scale. Earth is 4.6 billions of years old!! 6/10/2024 The “geologic spiral”: If the Earth’s whole history was equated to a 24-hours day, modern 6/10/2024 thinking humans (Homo sapiens ) would have arrived on the scene just about ten seconds ago. The Earth System 52 EXERCISES Media Support 1. Give two reasons why Earth’s shape is not a perfect sphere. 2. How does the chemical composition of Earth’s crust differ Earth’s Major Layers: from that of its mantle? From that of its core? http://bcs.whfreeman.com/webpub/geology/understandingearth 3. Explain how Earth’s outer core can be liquid while the mantle is 7e/qrcodes/animations/WHFGEO_earthsmajorlayers.html solid. 4. Earth’s mantle is solid, but it undergoes convection as part of the plate tectonic system. Explain why these statements are not contradictory. 5. Imagine you are a tour guide on a journey from Earth’s surface to its center. How would you describe the material that your tour group encounters on the way down? Why is the density of the material always increasing as you go deeper? 6/10/2024 54 6/10/2024 55 13