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Transcript
• • • • • • • • • • • • • 1 Planet Earth MAIN IDEA The major geologic features of Earth's surface are (1) the surface fluids (air and water), (2) the continents, and (3) the ocean basins. The characteristics of these features indicate that Earth is undergoing constant change. Earth is unique in the Solar System. SUPPORTING IDEAS 1. A comparison of Earth with other terrestrial planets provides an insight into the distinguishing characteristics of our planet and what makes it unique. 2. Earth's atmosphere is a thin shell surrounding the planet and is in constant motion. It is unique in the Solar System in that it is composed of 78% nitrogen and 21% oxygen. 3. The hydrosphere is another feature that makes Earth unique. It moves from the ocean to the atmosphere and over the surface in a great cycle. 4. The biosphere exists because of water. Although it is relatively small compared with other major layers of Earth, the biosphere has been a major geologic force operating at the surface. • • • • • • • • • 5. Continents and ocean basins are the principal surface features of Earth. 6. The continents consist of three major components: (a) shields, (b) stable platforms, and (c) belts of folded mountains. All these components show the mobility of the crust. 7. The ocean floor contains several major structural and topographic divisions: (a) the oceanic ridge (b) the abyssal floor, (c) seamounts, (d) trenches, and (e) continental margins. 8. Earth is a differentiated planet, with its materials segregated and concentrated into layers according to density. The internal layers based on composition are (a) crust, (b) mantle, and (c) core. The major internal layers based on physical properties are (a)lithosphere, (b) asthenosphere, (c) mesosphere, (d) outer core, and (e) inner core. Material within these units is in motion, making Earth a changing, dynamic planet. Earth’s Outermost Layers • The most dynamic portion of the Earth – Atmosphere • Thin gaseous envelope surrounding Earth – Hydrosphere • Water layer dominated by the oceans – Biosphere • All living things on the planet – Lithosphere • Rocky outer shell The Atmosphere • Insignificant fraction of Earth’s total mass (<0.01%) – Moves easily, interacts with oceans and landmasses • Circulation patterns are evident from space • Solar heat drives this circulation • Evaporation and precipitation of water play a role in circulation Hurricane Felix - 2007 The Atmosphere • Composition is unique in our solar system – 78% nitrogen – 21% oxygen (not present in early atmosphere) – Minor amounts of carbon dioxide, argon and water vapor • Formation of limestone in the ocean has trapped large amount of CO2 The Hydrosphere • Total mass of water on or near the Earth’s surface – Covers 71% of Earth’s surface – ~98% in oceans – 2% in glaciers, groundwater, lakes and streams (fresh water) – The presence of water moderates climates and shapes the Earth’s surface Earth Infrared satellite image of the Gulf Stream Iceberg The Biosphere • All life on Earth – Animals & plants on land, in the sea and air – Microorganisms, the most common form of life – Forms a narrow zone near the Earth’s surface Herbs & Weeds Microorganisms Figures from Brock; Biology of Microorganisms, 11th ed., Madigan and Martinko Microorganisms Microorganisms Mammal Phylogeny Birds: Diatryma phororhachids Diatrymidae Marine Reptiles Ammonoids - Parapuzosia The Biosphere • The diversity of life – 1.6 million known species • insects account for over one-half • mammals only ~4000 species (0.025%) – 30 million or more may exist – Local environment controls distribution • Temperature, pressure & chemistry • Wide range of environmental conditions The Biosphere • The biosphere as a geologic force – Current atmosphere produced by biosphere (Oxygen) – Ocean composition influenced by biosphere precipitation of calcium carbonate – Fossils fuels – Fossils record past Earth environments • Current living species account for only 10% of known species throughout geologic history Earth’s Internal Structure • The solid Earth has a layered structure – Layers defined by composition and physical properties – Compositional layers • crust - mantle - core – Physical layers • lithosphere - asthenosphere - mesosphere outer core - inner core Compositional Layers • Crust – Outermost compositional layer – Definite change in composition at the base of the crust – Crust may be divided into 2 types • Continental crust • Oceanic crust Compositional Layers • Crust – Continental crust • Thicker than oceanic crust - up to 75 km • Less dense - 2.7 g/cm3 • Strongly deformed • Much older - may be billions of years old Compositional Layers • Crust – Oceanic crust • Thinner than continental crust - about 8 km • More dense - 3.0 g/cm3 • Comparatively undeformed • Much younger - < 200 million years old • Composed of basalt Crustal Properties Crust Density continental ~2.8 g/cm3 oceanic ~3.2 g/cm3 Composition Thickness Felsic Thick: 20-70 km Mafic Thin: 2-10 km Age Old: up to 4 Byrs Young: <200 Mys Compositional Layers • Mantle – Largest layer in the Earth • 2900 km thick • 82% by volume • 68% by mass – Composed of silicate rocks with abundant iron and magnesium: Mafic • Density ranges from 3.2 to 5 g/cm3 • Fragments found in some volcanic rocks Compositional Layers • Core – Central mass about 7000km in diameter – Average density of 10.8 g/cm3 – 16% by volume, 32% of mass – Indirect evidence of composition • Metallic iron Physical Layers • Lithosphere – Crust + upper portion of the mantle – Solid & rigid – Thickness ranges from 10 km beneath oceans to 300 km in continental areas Physical Layers • Asthenosphere – Upper layer in the mantle – Temperature and pressure combine to allow rock to partially melt • Rocks are soft and plastic • Flow slowly, easily deformed – Boundary with lithosphere is defined by mechanical properties, not composition Physical Layers • Mesosphere – The region between the asthenosphere and the core – Higher pressure offsets higher temperatures – Rocks gain rigidity and mechanical strength Physical Layers • Outer Core – ~2270 km thick – Liquid, flows – Flow creates magnetic field • Inner Core – ~1200 km thick – Solid The Core • Seismic wave studies have provided primary evidence for existence and nature of Earth’s core • Specific areas on the opposite side of the Earth from large earthquakes do not receive seismic waves, resulting in seismic shadow zones • P-wave shadow zone (103°-142° from epicenter) explained by refraction of waves encountering core-mantle boundary • S-wave shadow zone (≥103° from epicenter) suggests outer core is a liquid • Careful observations of P-wave refraction patterns indicate inner core is solid Majors Features of the Continents • Shields – Large, flat areas of highly deformed crystalline rock - most more than 1 billion years old – Basement complex • Stable platforms (cratons) – Areas where the basement complex is covered by layered sedimentary rocks • Folded Mountain Belts – Young, linear regions of deformed rocks North American Craton Shield Western North American Mobile Belt Platform Eastern Nor American Mobile Be Major Features of the Oceans • Oceanic Ridge – 70,000 km long continuous feature – Broad ridge, highly fractured with a central rift valley – Fractures, perpendicular to the ridge, are common • Trenches – Lowest areas on Earth – Adjacent to chains of volcanoes Major Features of the Oceans • Abyssal Floor – Abyssal hills - small hills up to 900 m high • Cover 80+% of ocean floor • Most common landform on Earth – Abyssal plains - smooth area adjacent to continents • Sediment covered abyssal hills • Seamounts – Isolated peaks of submarine volcanoes Major Features of the Oceans • Continental Margins – Continental shelf - submerged portions of continents • Part of the continent, not the ocean basin • Arial extent has varied throughout geologic history –11% of continents are submerged today – Continental slope • Long slope from continents to ocean basin Ocean Basins Heat driven convection 1. Bottom water is warmed 2. It expands an is therefore less dense 3. It rises to the surface and then spreads out 4. Cooler water at the sides descends to fill the void A convective thunderstorm Plate Tectonics Basic idea of plate tectonics Earth’s surface is composed of a few large, thick plates that move slowly and change in size Intense geologic activity is concentrated at plate boundaries, where plates move away, toward, or past each other Combination of continental drift and seafloor spreading hypotheses in late 1960s The ‘Ring of Fire’ Juan de Fuca plate Intraplate volcanism Rising mantle plumes can produce localized hotspots and volcanoes when they produce magmas that rise through oceanic or continental crust. Hawaii is an example Composition? Hurricanes http://www.youtube.com/watch?v=_SLXYRJnYm0 http://www.rap.ucar.edu/weather/satellite/ Hurricane Felix - 2007 What do you need for hurricane formation? SST > 26.5 C; Coriolis force; weak wind shear Where and when do these conditions exist in the Atlantic? Surface Water Temperature (SST) Hurricanes are “Warm-Core Lows” High warm Low Note where rising and sinking motion occurs. Energy Conversion! • Hurricanes (a.k.a. Typhoons, Tropical cyclones) are giant machines for converting latent heat to kinetic energy! • Consider rain rate of 5 cm/day over an area of 500 km radius (typical for tropical depression, tropical storm, and hurricane) • Over a 7 day lifecycle, the energy released is equal to 50,000 1 MT nuclear explosions! • This is equivalent to the total explosive yield of the nuclear arsenals of the US and USSR at the height of the Cold War! “Storm Surge” causes some of the worst damage Folly Beach, South Carolina (Before Hugo) Folly Beach, South Carolina (After Hugo) http://www.geog.ucsb.edu/~joel/g110_w08/lecture_notes/sun_angle/anim_fall.gif http://www.geog.ucsb.edu/~joel/g110_w08/lecture_notes/sun_angle/anim_sum.gif Precambrian Hadean Earth 2004 - Fred Sulahria Heavy Bombardment Period Atmospheric Formation Hypothesis: Captured from Solar Nebula • Mostly Hydrogen and Helium • Would have been quickly lost If initially lost - where did the present atmosphere come from? 1. Accreted as hydrous minerals and outgassed from volcanoes 2. Returned to Earth from comets Secondary Atmosphere - Outgassing Initially Composed of: • Ammonia (NH3) • Hydrogen (H2) • Carbon dioxide (CO2) • Methane (CH4) • Water vapor (H2O) • Nitrogen (N2) Oceans “Raining” of the Oceans “Vaporization” of the Oceans Hadean Oceans Characteristics • Liquid Water existed at 4.4 Gyrs Evidence • Jack Hills Formation zircon crystals with water inclusions •“Ephemeral” (periodically vaporized) •solar system evidence for heavy bombardment and models • Acidic (water + carbon dioxide = carbonic acid) • no limestones, atmospheric models •acidic water (dissolves ions) •Probably “salty” • Stabilized by end of Hadean (about 3.8 Gyrs) • first limestones & sedimentary rocks