Physical Geology - Introduction To Earth PDF

College of Science  College of Science Physical Geology  Main Subjects: Geology & Physical Geology Origin of Earth Earth as a System Earth’s Internal Structure Dynamic layers Geologic Time Historical Notes about Geology Physic...

College of Science  College of Science Physical Geology  Main Subjects: Geology & Physical Geology Origin of Earth Earth as a System Earth’s Internal Structure Dynamic layers Geologic Time Historical Notes about Geology Physical Geology  Geology & Physical Geology  Geology means “the study of Earth”. (Geo = Earth & logy = Science) that gives Earth Science…… Physical Geology is the science that deals with the study of the materials constituting the earth, and the processes taking place above and beneath the earth’s surface. Physical Geology  Origin of the Earth The earth is one of the major eight planets that revolve around the sun. It was formed as the other planets of the solar system (the sun and the other planets) from a vast cloud of dust and gases called a Nebula. Physical Geology  Origin of the Earth Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune Physical Geology  Origin of the Earth Nebular Hypothesis This hypothesis suggests that the bodies of the solar system formed from an enormous nebular cloud composed mostly of hydrogen and helium with only small percentage of the heavier elements. Physical Geology  Origin of the Earth About 5 billion years ago, this cloud began to contract under its own gravitational influence, this contraction caused rotation of the cloud which became faster and faster as it contracted. The rotation caused the nebular cloud to flatten into a desk. Physical Geology  Origin of the Earth Smaller accumulations formed nuclei from which the planets formed. The sun was formed at the center of the desk. Physical Geology  Origin of the Earth  The atmosphere develops from volcanic gases. When the Earth becomes cool enough. Moisture condenses and accumulates. The oceans are born. Physical Geology  Spheres of the Earth There are four different “spheres” around the earth: 1. Hydrosphere 2. Atmosphere 3. Biosphere (ecosphere) 4. Lithosphere (geosphere) Physical Geology  Spheres of the Earth: Hydrosphere It includes all water bodies on the earth such as the oceans & seas, which constitute about 71% of the earth’s surface, the freshwater streams, lakes as well as the underground water. Fresh water is very important for life and also responsible for sculpting and creating many landforms on the earth. Physical Geology  Spheres of the Earth: Hydrosphere Hydrosphere covers about 70 % of Earth’s surface. Oceans represents 97% of Earth’s water. In the southern hemisphere, the area which is covered by water Oceans represents increase by about 20 % than on the 97% of Earth’s water northern hemisphere Physical Geology  Spheres of the Earth: Hydrosphere Fresh water and its distribution (Groundwater, Lakes, Streams and Glaciers) Physical Geology  Spheres of the Earth: Biosphere It includes all life on the earth either plant life or animal life, in the sea or on land. Physical Geology  Spheres of the Earth: Atmosphere Earth's atmosphere can be divided into five main layers. These layers are mainly determined by whether temperature increases or decreases with altitude. From lowest to highest, these layers are: Troposphere Stratosphere Mesosphere Thermosphere Exosphere Physical Geology  Spheres of the Earth: Atmosphere The atmosphere is primarily composed of: Nitrogen (N2, 78%) Oxygen (O2, 21%) Other Gases (Others, 1%) Physical Geology  Spheres of the Earth: Geosphere The lithosphere (geosphere) includes the crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth. The lithosphere is underlain by the asthenosphere, the weaker, hotter, and deeper part of the upper mantle. Physical Geology  Earth Materials  Elements combine in a variety of Earth materials.  Organic compounds – Carbon containing compounds. Most are residue from once living creatures. Include wood, peat, lignite, coal and oil. Geologically rare (decomposes in contact with oxygen). Physical Geology  Earth Materials  Elements combine in a variety of Earth materials.  Minerals – Inorganic crystalline solids. Comprise rocks and, hence, most of the earth. Most rocks on Earth are silicates (based on Si and O).  Glasses – Non-crystalline mineral-like matter.  Rocks – Aggregates of minerals. There are many types. Igneous – Cooled from a liquid (melt) Sedimentary – Debris cemented from pre-existing rock. Metamorphic – Rock altered by pressure and temperature. Physical Geology  Earth Materials  Metals – Solids made of metallic elements.  Melts – Rocks that have been heated to a liquid.  Magma – Molten rock beneath the surface.  Lava – Molten rock at the surface.  Volatiles – Materials that turn into gas at the surface.  H2O, CO2, CH4 and SO2  Volatiles are released from volcanic eruption. Physical Geology  Earth’s Internal Structure  We live on the thin outer skin of Earth.  Early perceptions about Earth’s interior were wrong.  Open caverns filled with magma, water and air.  Furnaces and flames.  We now know that Earth is comprised of layers.  The Crust.  The Mantle.  The Core. Outer Core. Inner Core. Physical Geology  Earth’s Internal Structure Physical Geology  Earth’s Internal Structure The information on the earth’s interior subdivisions was mainly obtained by analyzing seismic waves that were originated from earthquakes. Physical Geology  Earth’s Internal Structure: Crust It is the rigid outermost layer of the earth. It is divided into Oceanic crust & Continental crust. The oceanic crust ranges in thickness from 3-15 km and is composed of basalt (alkaline). It is chemically composed of iron and magnesium silicates and hence takes the name Sima (Silicon and magnesium). Physical Geology  Earth’s Internal Structure: Crust The Continental crust ranges in thickness from 20-70 km and is composed of granite (acidic). It is chemically composed of aluminum and potassium silicates and hence takes the name Sial (Silicon and aluminum). The Oceanic crust is denser than the continental crust and hence the mountains act as roots on the continents to substitute for the unbalance. Physical Geology  Earth’s Internal Structure: Mantle The mantle underlies the crust and separated from it by Moho discontinuity (Mohorovic). It has a depth to about 2900 km and is composed of denser material, mainly silicates of iron, magnesium, sodium and aluminum. Although the mantle behaves like a solid in transmitting earthquake waves, mantle rocks are able to flow at a slow rate. Physical Geology  Earth’s Internal Structure: Lithosphere The mantle is divided into: Lower mantle or mesosphere Upper mantle or Asthenosphere The upper rigid part of the Asthenosphere together with the crust is known as the Lithosphere. Oceanic Crust Continental Crust Physical Geology  Earth’s Internal Structure: Core The core is the innermost layer of the earth. It is composed mainly of nickel and iron together with other elements. It is divided into outer core which is liquid and able to flow and circulates as the earth rotates generating the earth’s magnetic field. The inner core is on the other hand solid and made up of the Earth’s Internal Structures same material as the outer core. Physical Geology  Earth’s Internal Structure: Core Physical Geology  Earth’s Internal Structure Mechanical Layers Earth is divided according to the mechanical behavior of its rocks to two distinctive zones: 1) The Lithosphere: 2) The Astenosphere: This zone consists of cool situated beneath the rigid shell with an average lithosphere to a depth of thickness of 100 km. It about 660 km. It consists of includes the crust and the soft, relatively week rocks. upper part of the mantle. Physical Geology  Dynamic Earth Earth is a dynamic planet. There are two types of processes that change the earth's surface which are: Destructive & Constructive processes Destructive processes are those Constructive processes such as that wear away the land such as volcanism & mountain building weathering and erosion. increase the average elevation of the land. Physical Geology  Dynamic Earth Destructive Processes Physical Geology  Age of the Earth The concept of geologic time is new to many non- geologists because people are accustomed to dealing with time measured in hours, days, weeks, & years. Those who study geology must deal with vast time periods: millions or billions of years. When viewed in the context of Earth's 4.6 billion year historic, a geologic event that occurred 100 million years ago may be described as "recent" by a geologist. Physical Geology  Age of the Earth Before the 19th century, it wasn’t possible to determine the absolute age of the earth. Only a relative age could be given to the different rock layers. Relative age: Events are placed in their proper sequence or order without knowing their absolute age in years. This is done by applying the following principles: The law of superposition The principle of faunal succession Physical Geology  Law of Superposition In any undeformed sequence of sedimentary rocks or lava flows, each layer is older than the one above it and younger than the one below it. Physical Geology  Principle of Faunal Succesion Fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content. Geologists collected fossils from countless rock layers around the world and used these fossils to identify rocks of the same age in widely separated places and to build the geologic time scale. Physical Geology  Fossils Fossils are remains or traces of ancient animals and plants. Physical Geology 38  Absolute Age In the twentieth century, the discovery of radioactive materials helped the scientists to give an absolute age for the events in the earth’s history. The earth’s age is estimated to be about 4.6 billion years. 65 to present 65-245 245-570 570-4600 Cenozoic Mesozoic Paleozoic Precambrian Age in Millions of Years Physical Geology 39  Absolute Age Physical Geology  Geologic Time Scale Life started on the earth about 600 M.Y., this time is called Phanerozoic (13 % of Earth History). The other 4000 M.Y. are called Precambrian. There was little life in the Precambrian represented by first one-celled and first multi-celled organisms Physical Geology 41  Geologic Time Scale The Phanerozoic Eon is divided into three Eras: Paleozoic, Mesozoic & Cenozoic. Each of these eras is further subdivided into: periods & epochs. Physical Geology 42  Geologic Time Scale Physical Geology 43  Historical Notes about Geology The geological thinking during the 17th & 18th centuries was dominated by two major thinking "schools". catastrophism uniformitarianism Physical Geology 44  Catastrophism The catastrophism doctrine (or principle) strongly influenced people thinking about the dynamics of Earth. The theory suggested that Earth's landforms had been formed mainly by great catastrophes. Features such as mountains and canyons, which today we know took great periods of time to form, were explained as having been formed by sudden, often worldwide disasters produced by unknown causes that no longer operate. Physical Geology 45  Uniformitarianism (The Birth of Geology) The late 1700s is considered as the beginning of modern geology. At that time, James Hutton, a Scottish physician published his Theory of the Earth. In his book, Hutton proposed for the first time, a principle that came to be known as the doctrine of uniformitarianism. It represents the fundamental principle of modern geology. The doctrine states that physical, chemical, and biological laws that operate today have also operated in the geologic past. This idea is commonly stated as "the present is the key to the past". Physical Geology 46  Uniformitarianism (Hutton’s Theory) The Present is the key to the Past The physical, chemical and biological processes that operate today have also operated in the geologic past. Physical Geology 47  Uniformitarianism (Hutton’s Theory) Although the work of Hutton laid the cornerstone of modern geology, but it is believed that the English geologist Sir Charles Lyell was the person who set the basic principles of modern geology. Between 1830-1872, he produced 11 editions of his book "Principles of Geology". He was able to show in a more convincing way that geologic processes observed today can be assumed to have operated in the past. The acceptance of the principle of uniformitarianism meant the acceptance of a very long history for Earth. Although processes vary in their intensity, they still take a very long time to create or destroy major landforms. Physical Geology 48  End of Chapter 1 Chapter 2: Plate Tectonics Physical Geology 49