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Chapter One Introduction to Geology Geology literally means "study of the Earth." Physical geology examines the materials and processes of the Earth. Historical geology examines the origin and evolution of our planet through time. • Geology is an evolving science - the theory of plate tectonics was just accepted in the 1960's. • • Geology is an extremely controversial science - the theory of evolution (paleontology) is central to geology. Geology seeks to understand the origin of our planet and our place in the Universe - answers to these questions are also posed outside of the realm of science. History of Early Geology Catastrophism (James Ussher, mid 1600s) - He interpreted that the Earth was created at 4004 B.C. Subsequent workers then developed the notion of catastrophism, which held that the the Earth’s landforms were formed over very short periods of time. Uniformitarianism (James Hutton, late 1700s) - He proposed that the same processes that are at work today were at work in the past. Summarized by “The present is the key to the past.” Hutton recognized that time is the critical element to the formation of common geologic structures. Uniformitarianism is a basic foundation of modern geology. Although catastrophism was abandoned, there is certainly evidence that sudden events do occur. From space, Earth looks small, finite and fragile. What's the first thing that you notice about our planet when you see this image? The Earth is composed of several integrated parts (spheres) that interact with one another: atmosphere hydrosphere solid earth (lithosphere) biosphere The Earth System Hydrosphere: Oceans are the most prominent features of our (blue) planet. The oceans cover ~71% of our planet. Atmosphere: the swirling clouds of the atmosphere represent the very thin blanket of air that covers our planet. It is not only the air we breathe, but protects us from harmful radiation from the sun. The Earth System Biosphere: includes all life on Earth concentrated at the surface. Plants and animals don't only respond the their environment but also exercise a very strong control over the other parts of the planet. Solid Earth: represents the majority of the Earth system. Most of the Earth lies at inaccessible depths. However, the solid Earth exerts a strong influence on all other parts (ex. magnetic field). Theories of the Origin of the Universe • Theological “Theories”: • Scientific Theories: – Continuous creation – Big Bang Theory – the commonly accepted theory( given by Georges Lemaître in 1927) The Big Bang theory • • • • The theory that the universe was expanding implies the universe must have been smaller in the past than it is today. It implies that the universe must have had a beginning. Astronomers today believe the universe exploded outward from a single point. This idea is known as the Big Bang theory. The Big Bang theory • • The Big Bang theory says the universe began as a huge explosion between 10 billion and 20 billion years ago. According to this theory, all matter and energy started in a space smaller than the nucleus of an atom. Big “Bang Theory” • Technically, there was no “bang” • Technically, galaxies are not moving away from each other • Reality: space expands – When there are more space between galaxies, they “move” away from each other – Analogy: dots on an expanding balloon Evidence for the Big Bang • Theory predicts an expanding universe – Confirmed by Red Shift (Doppler effect) in spectrum • Theory predicts cosmic background radiation – Background radiation was discovered in 1964 by Arno Penzias and Robert Wilson, who later won the Nobel Prize for this discovery Doppler Shift • In the 1800s, Christian Doppler discovered that when the source of a sound wave is moving, its frequency changes. • The change in sound you hear is caused by a Doppler shift. • Doppler shift is related to the net change between the source of the waves and the observer. Doppler Shift • Doppler shift also occurs with electromagnetic waves, such as visible light, X-rays, and microwaves. • This phenomenon is an important tool used by astronomers to study the motion of objects in space. The expanding universe • • The faster the source of light is moving away from the observer, the greater the redshift. The opposite (blueshift) happens when an object is moving toward the observer. The expanding universe • • Edwin Hubble in 1929 discovered that the farther away a galaxy was, the faster it was moving away from Earth. This concept came to be known as the expanding universe. Evidence for the Big Bang theory • • In the 1960s, Arno Penzias and Robert Wilson were trying to measure electromagnetic waves given off by the Milky Way. The “noise” these scientists found was the cosmic microwave background radiation predicted by the Big Bang theory. Evidence for the Big Bang theory • • The proportion of hydrogen to helium is consistent with the physics of the Big Bang. If the universe were significantly older, there would be more heavy elements present compared with hydrogen and helium. Planetary systems • A star with orbiting planets is called a planetary system. • Scientists now believe that planets are a natural by-product of the formation of stars. How the solar system formed Nebular Hypothesis • Scientists think that the solar system was formed out of the same nebula (vast cloud of dust and gas that created the Sun. A diffuse, spherical slowly rotating nebula begins to contract As a result of contraction and rotation, a flat rapidly rotating disc is formed with matter concentrated at the centre Enveloping gas and dust form grains that collide and clump together to form protoplanets SUN The Sun is the Solar System's star, and by far its chief component. Its large mass (332,900 Earth masses) produces temperatures and densities in its core great enough to sustain nuclear fusion which releases enormous amounts of energy, mostly radiated into space as electromagnetic radiation. Also known as ‘yellow dwarf’ sun is one of the brightest stars. Dimmer and cooler stars are known as red dwarfs. 85% Stars are red dwarfs. Terrestrial or inner planets: Mercury, Venus, Earth, Mars Mercury: smallest planet, no satellite, large iron core, no atmosphere Venus:close in size to Earth, (0.815 Earth mass) and like Earth, has a thick silicate mantle around an iron core, a substantial atmosphere, it is much drier than Earth and its atmosphere ninety times as dense, no natural satellites, hottest planet, with surface temperatures over 4000C most likely due to the amount of greenhouse gases in the atmosphere. Earth:the largest and densest of the inner planets, is the only place in the universe where life is known to exist, hydrosphere is unique among the terrestrial planets. Earth's atmosphere is radically different from those of the other planets, having been altered by the presence of life to contain 21% free oxygen, has one natural satellite, the moon, the only large satellite of a terrestrial planet in the Solar System. Mars: smaller than Earth and Venus (0.107 Earth masses), an atmosphere of mostlyCO2, surface, peppered with vast volcanoes such as Olympus Mons, red colour comes from iron oxide (rust) in its soil, has two tiny natural satellites). Asteroid belt: occupies the orbit between Mars and Jupiter, thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter. Ceres is the largest body in the asteroid belt Outer solar system: Gas giants or Jovian planets: not composed of rock or other solid matter, mainly composed of hydrogen and helium Jupiter:at 318 Earth masses, composed largely of hydrogen and helium. Jupiter's strong internal heat creates a number of semi-permanent features in its atmosphere, such as cloud bands and the Great Red spot. Jupiter has 63 known satellites. Saturn:distinguished by its rings, has several similarities to Jupiter, such as its atmospheric composition. Although Saturn has 60% of Jupiter's volume, it is the least dense planet in the Solar System. The rings of Saturn are made up of small ice and rock particles. Saturn has 62 satellites Ice Giants: Composed of water ammonia and methane ice Uranus: lightest outer planet, 14 earth masses, 27 known satellites, orbits the sun on its side with axial tilt over 90 degree. Neptune: smaller but denser, 17 earth masses, 13 satellites Inside the Earth Composition (What it is made of) • Crust • Mantle • Core Earth’s Layers • How are the earth’s layers similar to an egg? • Shell=crust • Egg white=mantle • Yolk=core Average density of the earth: 5.52 grams/cm3. Continental Crust: 2.7 to 3.0 Oceanic crust: 3.0 to 3.3 Mantle (silicates): 3.3 to 5.7 Outer Core (liquid): 9.9 to 12.2 Inner Core (solid): 12.6 to 13.0 How do we know about the interior of the earth ? 1. Seismology studies 2. Gravity measurements 3. Magnetic studies Types of seismic waves 1. P waves (compressional waves) 2. S waves or shear waves P waves travel 1.7 times faster than S waves. S waves can only travel in a solid medium AS SEISMIC WAVES TRAVEL FROM MATERIAL OF ONE SPEED AND DENSITY TO ANOTHER THE INCIDENT WAVES ARE REFLECTED AND TRANSMITTED (REFRACTED) BOTH THE ANGLES AND SIZE (AMPLITUDE) OF THE WAVES CHANGE, DEPENDING ON THE VELOCITY AND DENSITY CHANGE THIS EFFECT LETS US STUDY EARTH STRUCTURE (AND IS USED IN LENSES, EYEGLASSES, ETC. FOR LIGHT) Physical Structure of the Earth (5 Layers) • Lithosphere- rigid outer layer (crust) • Asthenosphere- solid rock that flows slowly (like hot asphalt) • Mesosphere- middle layer • Outer Core- liquid layer • Inner Core- solid, very dense The Crust The Earth's Crust is like the skin of an apple. It is very thin in comparison to the other three layers. The crust is only about 3-5 miles (8 kilometers) thick under the oceans (oceanic crust) and about 25 miles (32 kilometers) thick under the continents (continental crust). The crust is composed of two rocks. The continental crust is mostly granite. The oceanic crust is basalt. Basalt is much denser than granite. Because of this the less dense continents ride on the denser oceanic plates. Properties of the Crust Continental Crust Depth : 20 to 70 km, average 30 to 40 km Composition: felsic, intermediate, and mafic igneous, sedimentary, and metamorphic rocks Age: 0 to 4 b.y. Summary: thicker, less dense, heterogeneous, old Oceanic Crust Depth : ~7 km Composition: mafic igneous rock (basalt & gabbro) with thin layer of sediments on top Age: 0 to 200 m.y. Summary: thin, more dense, homogeneous, young Oceanic and Continental Crust The Mantle The Mantle is the largest layer of the Earth at 2900 km thick. The middle mantle is composed of very hot dense rock that flows like asphalt under a heavy weight. The movement of the middle mantle (asthenosphere) is the reason that the crustal plates of the Earth The Lithosphere The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the Lithosphere. The Lithospheric Plates The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, semirigid asthenosphere. The Lithosphere • Lithosphere= the crust and the uppermost part of mantle The Asthenosphere • Asthenosphere= the fluid like portion of the mantle that lies just below lithosphere. The lithosphere “floats” on the asthenosphere Convection Currents The middle mantle "flows" because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again -repeating this cycle over and over. The Outer Core The core of the Earth is like a ball of very hot metals. The outer core is so hot that the metals in it are all in the liquid state. The outer core is composed of the melted metals of nickel and iron. The Inner Core The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move about like a liquid, but are forced to vibrate in place like a solid. The Core • Inner core: The inner core is solid and unattached to the mantle, suspended in the molten outer core. It is believed to have solidified as a result of pressure-freezing which occurs to most liquids when temperature decreases or pressure increases. LOW VELOCITY ZONES Schematic view of the interior of Earth. 1. continental crust - 2. oceanic crust - 3. upper mantle - 4. lower mantle - 5. outer core - 6. inner core - A: Mohorovičić discontinuity - B: Gutenberg Discontinuity C: Lehmann discontinuity 1. Mohorovicic Discontinuity or ‘Moho” Seismic velocities tend to gradually increase with depth in the mantle due to the increasing pressure, and therefore density, with depth. However, seismic waves recorded at distances corresponding to depths of around 100 km to 250 km arrive later than expected indicating a zone of low seismic wave velocity. Furthermore, while both the P and S waves travel more slowly, the S waves are weakened. This is interpreted to be a zone that is partially molten. Alternatively, it may simply represent a zone where the mantle is very close to its melting point for that depth and pressure that it is very "soft." Then this represents a zone of weakness in the upper mantle. This zone is called the asthenosphere or "weak sphere." MOHO Lehman Siesmic Discontinuity / The InnerCore A sudden increase in P wave velocities at a depth of 5150 km indicates the presence of another discontinuity. This velocity increase is consistent with a change from a molten outer core to a solid inner core. Gutenberg discontinuity Lehman discontinuity Gutenberg Seismic Discontinuity/Core-Mantle Boundary Gutenberg (1914) explained that as the result of a molten core beginning at a depth of around 2900 km, S waves could not penetrate this molten layer and P waves were (bent). severely slowed and refracted What Causes the Earth's Magnetic Field? The outer core is a hot, electrically conducting liquid within which convective motion occurs. This conductive layer combines with Earth's rotation to create a dynamo effect that maintains a system of electrical currents known as the Earth's magnetic field. The discovery of the liquid outer core allowed another hypothesis: the geodynamo. Iron, whether liquid or solid, is a conductor of electricity. Electric currents would therefore flow in molten iron. Moving a flowing electric current generates a magnetic field at a right angle to the electric current direction (basic physics of electromagnetism). This convective motion would displace the flowing electric currents thereby generating magnetic fields. The magnetic field is oriented around the axis of rotation of the Earth. Practice Quiz Question • Can you label the following layers? What are the geologic landforms on the earth ? When you think of landforms, you might think of mountains or valleys. These are continental landforms, or landforms on the continents. Landforms are also found under the ocean’s water. These are called oceanic landforms. Continental vs. Oceanic Landforms • Canyon • Valley • Volcano • Mountain range • Low hills or plains • Trench • Rift • Seamount • Mid-ocean ridge • Ocean basin and abyssal plains Plains • Plains are large flat areas of land that are relatively low. A plain found in the ocean is called an abyssal plain. • A mountain has high elevations with steep sides and pointed tops. The top of the mountain is a peak, or summit. Circum-Pacific belt Alpine-Himalayan Belt Shield areas: Most stable parts of the continents. Rocks are as old as 3.8 billion Mountain range of the ocean : Ocean ridge system 65000 km continuous belt around the globe Mid-Ocean Ridge On the bottom of the ocean, there is a central ridge, or mountain range, that divides the ocean floor into two parts. This underwater volcanic mountain is the midocean ridge. It is more than 50,000 km in length DID YOU KNOW? The Earth’s longest mountain range is underwater ? Valleys • Valleys are low, narrow areas on Earth’s crust. On land, valleys are usually formed by erosion. • Valleys in the ocean are called a rift zone, or rift valley. The most extensive rift valley is located along the crest of the mid-ocean ridge www.inewscatcher.com/timages/9f26ca47 ac9ab0 Canyon and Trenches • A canyon has steep, rocky walls and is usually formed by water erosion like the Grand Canyon. • Ocean trenches have a much lower elevation than the surrounding area and is caused by one plate sliding under another plate. Trenches The many steep-sided canyons and deep, narrow valleys in the bottom of the ocean are trenches. Ocean trenches are the deepest part of the ocean basin and are deeper than any valley found on land. Did you Know? The Marianas Trench in the Pacific Ocean is the deepest trench in the world. It is nearly 7 miles (11 kilometers) below sea level. Mount Everest is only 5.5 miles (9 kilometers) above sea level. visual.merriam-webster.com/.../ocean-floor.jpg catastrophemonitor.com/public_html/images/art. A volcano is a mountain that opens downward to a pool of molten rock below the surface of the earth. When pressure builds up, eruptions occur. Gases and rock shoot up through the opening and spill over or fill the air with lava fragments. Eruptions can cause lateral blasts, lava flows, hot ash flows, mudslides, avalanches, falling ash and floods. Volcano eruptions have been known to knock down entire forests. An erupting volcano can trigger tsunamis, flashfloods, earthquakes, mudflows and rockfalls. Seamounts Volcanic cone shaped peaks that dot the ocean floor are called seamounts. Most are found in the Pacific Ocean. Most seamounts began life as volcanoes formed over hot spots in the ocean floor Guyots A guyot /ɡiˈoː/, also known as a tablemount, is an isolated underwater volcanic mountain, with a flat top over 200 meters (660 feet) below the surface of the sea. Guyots are most commonly found in the Pacific Ocean. Guyots show evidence of having been above the surface with gradual subsidence through stages from fringed reefed mountain, coral atoll, and finally a flat topped submerged mountain. Their flatness is due to erosion by waves, winds, and atmospheric processes What are the landforms on the ocean floor? The amazing ocean floor is made up of three parts: •the continental shelf •the continental slope •the deep blue sea Continental Shelf The edges of the continents slope down from the shore into the ocean. The part of the continent located under the water is the continental shelf. In some places the shelf is fairly shallow and in other places it becomes very deep. The steep slope where the continental shelf drops to the bottom of the ocean floor is called the continental slope. The depth of the water increases greatly here. Quick Quiz 1. The ocean is a big, flat featureless plain. True false 2. or False The steep part where the continental shelf slopes down to the deepest part of the ocean is called the continental slope. True true or False 3. What are the deepest parts of the ocean called? a. Deep-sea trenches b. Abyssal plains c. Continents d. Seamounts Deep sea trenches 4. What is a seamount? a. A scientist who studies the ocean floor b. Deep-sea trench c. A fancy seagull d. A volcano that formed over a hot spot on the ocean floor. How can we classify and illustrate natural processes as constructive or destructive? Constructive – Processes that create landforms Destructive – Processes that destroy landforms Natural Processes that can affect Earth’s oceans and landforms include: • Weathering – a term used to describe processes that break down rocks at or near the surface of the earth. Water is an important cause of weathering. • Erosion – the movement of sediments and soil by wind, water, and gravity • Deposition – the dropping, or depositing, of sediments by water, wind, or ice. Deposition builds up new land on Earth’s surface, like a delta at the end of a river or the pile up of a sand dune in a desert. • Landslides – mass movements of land due to gravity. • Volcanic Eruptions – Volcanoes can change the Earth’s surface. When the magma erupts from the volcano, the top of the mountain can be changed. The lava and ash can destroy forests and bury fields. Eruptions can even change weather patterns. • Earthquakes – vibrations on the surface of the Earth caused by sudden movement in Earth, often along a fault line. Large earthquakes can cause landslides. Earthquakes under the ocean can cause huge waves, called tsunamis that destroy land and cause great damage on shore. • Floods – rapid erosion can take place and move soil and sediments away. When the flood recedes, new sediment is left behind and can build up rich soil deposits. What are examples of ways natural processes can be both destructive and constructive? Constructive forces Destructive forces Both Kinds of forces Acknowledged sources 1.teachers.greenville.k12.sc.us/.../Geological%20Feature s%20of%20the%20Earth.ppt 2.www.livingston.org/15262082112049837/.../Inside_th e_Earth.ppt 3.teacherweb.com/TX/FriendswoodJrHigh/So/EarthInterior.ppt 4.www.ichthus.info/PowerPoint/BigBangand-Beyond.ppt 5.www.cpo.com/home/.../2/.../PESChp28U niverse3.ppt 6.www.pfm.howard.edu/astronomy/Universe.ppt 7. science.pppst.com/geology.html