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Lecture Outlines Natural Disasters, 5th edition Patrick L. Abbott Energy Flows in Earth History and Natural Disasters Natural Disasters, 5th edition, Chapter 2 Christiane Stidham, Stonybrook University Energy Sources of Disasters Four primary energy sources fuel Earth processes: • Impact of extraterrestrial bodies – Asteroids and comets; abundant in early Earth history, rare now • Gravity – Mass of Earth pulls objects (glaciers, hillsides) downhill • Earth’s internal heat – As Earth cools, heat flows from interior to surface – Volcanic eruptions, earthquakes – Plate tectonics; formation of continents, atmosphere and oceans • The Sun – Evaporation of water into atmosphere produces weather – Hailstorms, lightning, tornadoes and hurricanes Origin of the Sun and Planets • Solar system began as rotating spherical cloud of gas, ice, dust and debris • Gravitational attraction brought particles together into bigger and bigger particles • Cloud contracted, sped up and flattened into disk • Formation of Sun – Greatest accumulation of matter (H and He) at center of disk – Temperature at center increased to 1 million degrees centigrade – Nuclear fusion of hydrogen (H) and helium (He) began, producing solar radiation Origin of the Sun and Planets • Formation of planets – Rings of concentrated matter formed within disk – Particles within rings continued to collide to form planets – Inner planets (Mercury, Venus, Earth and Mars) lost much gas and liquid to solar radiation, becoming rocky (terrestrial) – Outer planets retained gas and liquid, as gas planets • Impact origin of the Moon – Early impact of Mars-sized body with Earth – Impact generated massive cloud of dust (from Earth’s crust and mantle) and gas which condensed to form Moon – Lightweight gases and liquids lost to space – Lesser abundance of iron (from Earth’s core) in Moon Earth History • Earth began as aggregating mass of particles and gases – Aggregation took 30 to 100 million years – Occurred about 4.57 billion years ago • Process of aggregation created huge amounts of heat • As temperature rose above 1,000 centigrade, iron melted – Liquid iron is denser than remaining rock, so sank toward center of Earth to form inner and outer core – Release of gravitational energy produced additional heat – Remaining rock melted, allowing low-density material to rise – Low-density material formed crust, oceans and atmosphere Earth History • • • • 3.9 billion years ago: large oceans, small continents 3.5 billion years ago: life (photosynthetic bacteria) 2.5 billion years ago: large continent 1.5 billion years ago: plate tectonics Earth History Analogy with Mother Earth, 46-year-old woman: (1 Mother Earth year = 100 million geologic years) • First seven years unaccounted for • 42 years old: life appeared on continents • 45 years old: flowering plants • 8 months ago: dinosaurs died out • Last week: human ancestors evolved • Yesterday: humans evolved • Last hour: discovered agriculture, settled down • 1 minute ago: Industrial Revolution The Layered Earth • Differentiated into layers of increasing density • Center of Earth: Iron-rich core 7,000 km in diameter – Inner core is solid and 2,450 km in diameter – Outer core is liquid and has viscous convection currents, responsible for Earth’s magnetic field • Surrounding core is Earth’s mantle, 2,900 km thick – Stony in composition (like chondritic meteorites) • Low-density elements have been ‘sweated’ out of the mantle to form the crust, atmosphere and oceans Volcanoes and the Origin of the Ocean, Atmospheres and Life • Volcanic gases: – Hydrogen (H), oxygen (O), carbon (C), sulfur (S), chlorine (Cl), nitrogen (N) • Combine to make: – Water (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen sulfide (H2S), carbon monoxide (CO), nitrogen (N2), hydrogen (H2), hydrochloric acid (HCl), methane (CH4), and others • Dominant volcanic gas is water vapor – more than 90% Volcanoes and the Origin of the Ocean, Atmospheres and Life • Volcanic rocks: – Oxygen (O), silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), magnesium (Mg), sodium (Na), potassium (K) • 4.5 billion years of volcanism has brought light weight elements to the surface to make up – – – – Continents Oceans Atmosphere CHON (carbon, hydrogen, oxygen, nitrogen) elements of life The Layered Earth • Layers can be described in terms of – Different density (resulting from different chemical and mineral compositions) or – Different strength • Describing layers in terms of density: – Crust overlies mantle • Describing layers in terms of strength: – Lithosphere overlies asthenosphere • Lithosphere is rigid (solid rock) • Asthenosphere is fluidlike (plastic rock) The Layered Earth • Asthenosphere is plastic – “Possession of a structure weak enough to yield to an influence, but strong enough not to yield all at once” • • • • About 250 km thick Comes to surface at mid-ocean ridges Lies more than 100 km below surface elsewhere Allows Earth to be oblate spheroid (flattened during rotation; like Solar System during formation) • Allows continents to ‘float’ atop the mantle, by principles of isostasy Isostasy • Isostasy: Less dense materials float on top of more dense materials (i.e. iceberg floating in ocean) • Earth is a series of density-stratified layers • Core – densities up to 16 gm/cm3 • Mantle – densities from 5.7 to 3.3 gm/cm3 • Continents (crust) – densities around 2.7 gm/cm3 • Oceans – densities around 1.03 gm/cm3 • Atmosphere – least dense Isostasy Examples of isostasy: • Impoundment of water in Lake Mead behind Hoover Dam caused area to sink 175 mm over 15 years • Scandinavia is currently rising (about 200 m so far) – Had been depressed under weight of ice sheets during last Ice Age (since 10,000 years ago) – Ground ruptures and earthquakes are present – Viking ship buried in the harbor mud of Stockholm was lifted above sea level – Another 200 m of uplift is likely Behavior of Materials • Gas, solid and liquid are obvious terms, but should be considered with respect to time – Over longer time periods, solids may behave as liquid • Glacier is solid ice, yet flows downhill as ultrahigh viscosity liquid over time span of years • Elastic deformation is recoverable – object returns to original shape • Ductile deformation is permanent – stress applied over long time or at high temperatures • Brittle deformation is permanent – stress applied very quickly to shatter or break object Internal Sources of Energy • Impact energy – Tremendous numbers of smaller bodies hit the Earth early after its formation, converting energy of motion to heat • Gravitational energy – As Earth pulled to smaller and denser mass, gravitational energy was released as heat Heat from both of these early sources is still flowing to the surface today, as heat conducts very slowly through rock Internal Sources of Energy Radioactive elements • Unstable radioactive atoms decay and release heat • Early Earth had much larger amount of short-lived radioactive elements and therefore much greater heat production than now • Radioactive decay process: – Measured by half-life: length of time for half the present number of atoms of a radioactive element (parent) to disintegrate to decay (daughter) product – Half-lives against time is negative exponential curve Internal Sources of Energy • Sum of internal energy from impacts, gravity and radioactive elements (plus tidal friction energy) is very large • Internal temperatures have been declining since early Earth maximum, but still significant enough to cause plate tectonics, earthquakes and volcanic eruptions Age of the Earth • Oldest Solar System materials are 4.57 billion years old – Measured using radioactive elements in Moon rocks and meteorites • Oldest Earth rocks (found in northwest Canada) are 4.055 billion years old • Oldest Earth materials (zircon grains from Australian sandstone) are 4.4 billion years old Age of the Earth • Earth must be younger than 4.57 billion years old materials that formed the planet – Seems that Earth has existed as coherent mass since about 4.54 billion years ago – Probably took 30 million years (0.03 billion years) for Earth to form • Collision that formed the Moon seems to have occurred between 4.537 and 4.533 billion years ago • Earth must be older than 4.4 billion years old zircons Radioactive Isotopes Elements defined by number of positively charged protons – Isotopes are different forms of the same element with different numbers of neutrons – Radioactive isotopes are unstable and release energy through their decay process to more stable isotopes • Nuclear fission: – Parent atom sheds particles to become smaller daughter atom – Alpha particle: two protons and two neutrons (helium atom) – Beta particle: electron – Gamma radiation: lowers energy level of nucleus • Knowing the half-life of radioactive isotopes allows us to use their quantity as clock to date rocks Radioactivity Disasters • Chernobyl disaster of 1986, in Ukraine – Explosion released 185 million curies of radioactive atoms affecting everyone from Scandinavia to Greece – 31 workers were killed and 165,000 later deaths blamed on accident, with more to come • Can such a thing occur in nature? Depends on relative amounts of U-238 and U-235: – U-235 makes up 0.7% of uranium ore – Uranium ore used in reactors is enriched to 2-4% U-235 – Because U-235 decays more rapidly than U-238, at some point in the past all uranium ore would have had about 2-4% U-235 – Sites in West Africa were natural nuclear reactors about 2 billion years ago, at about 400 degrees centigrade temperatures Gravity • Gravity is attraction between objects: – Two bodies attract each other with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them – Planetary mass can be considered concentrated at its center • Gravitational effects of Sun and Moon on Earth – – – – – Moon’s mass is about 1/80 of Earth Sun’s mass is 332,000 times that of Earth Moon is 386,000 km from Earth Sun is 150,000,000 km from Earth Sun’s gravitational pull on Earth is 170 times that of the Moon Gravity • Tidal energy is generated by interactions of gravity between Earth, Sun and Moon • Tides are caused by differences in gravitational pull from one part of Earth to another – Sun’s pull in mostly uniform throughout Earth, so small tides – Moon’s pull is much greater on facing side than on opposite side, so Moon tides are about twice magnitude of Sun’s tides Gravity • Tides affect land, water and air – most obvious in ocean • Moon’s tidal bulges move relative to Sun’s tidal bulges – Both tides coincide twice monthly (spring and neap tides) • Tidal motions within the Earth cause: – Earth’s and Moon’s rotations to slow down – Earth and Moon to move farther apart – Days become longer – Years have fewer days • 370 million years ago, Earth day was 22 hours and year had 400 days Energy, Force, Work, Power and Heat • Energy: Capacity to do work – Potential energy: potential to do work (PE = mgh) – Kinetic energy: energy of motion (KE = ½ mv2) • • • • Work: Force times distance (W = Fd = mad) Force: Mass times acceleration (F = ma) Power: Rate at which work occurs (P = W/T) Heat: Capacity to raise the temperature of a mass (energy) m (mass), g (gravity), h (height), v (velocity), a (acceleration), d (distance) External Sources of Energy All sources of internal heat flow on Earth are dwarfed by 5,300 times greater heat flow to Earth from Sun • Solar radiation: –43% visible wavelengths –49% near-infrared wavelengths –7% ultraviolet wavelengths –Short wavelength • Sun’s energy: –30% reflected back to space at short wavelengths (albedo) –47% absorbed as heat –23% evaporates water and begins hydrologic cycle Hydrologic Cycle • Sun’s heat evaporates water and plants transpire water into atmosphere • Atmospheric moisture condenses and precipitates • Sun’s energy is stored in water and water vapor • Equatorial regions receive excess insolation (solar radiation), while in polar regions radiation back to space exceeds insolation • Imbalance between equatorial and polar regions cause ocean currents and winds, transferring heat Hydrologic Cycle • 97.1% of Earth’s water is in oceans • Of remaining 2.9%: – – – – 68% in glaciers 21% underground 10% in atmosphere 1% in rivers, lakes, inland seas and soil moisture • Water in atmosphere holds, transports and releases solar energy, distributing heat around the Earth Water – The Most Peculiar Substance on Earth? • • • • • • • • • Present in liquid, solid and gas states Highest heat capacity except liquid ammonia Highest heat conduction Highest latent heat of vaporization Highest latent heat of fusion except ammonia Bipolar molecule easily able to bond with ions Highest dielectric constant of liquids Highest surface tension of liquids Expands 9% when frozen (most substances shrink) Processes of Construction vs. Destruction Rock Cycle: • Internal heat melts rock to magma, which rises and cools to form igneous rocks – Process of Construction • External heat from Sun drives hydrologic cycle that weathers and erodes rocks into sediments, which are transported and deposited – Process of Destruction Processes of Construction vs. Destruction Rock Cycle: • Continents could be eroded to sea level in 45 million years (1% Earth history), but processes of construction keep raising continents and forming new landmasses • The power of these Processes of Construction and Destruction causes disasters! Impacts with Asteroids and Comets Earth travels 950 million km around the Sun each year with an orbital speed of 108,000 km/hr kinetic energy = 2.7 x 1033 joules • When this kinetic energy is brought into collision with another body, effects are catastrophic and worldwide: – Asteroid: 65,000 km/hr – Comet: 150,000 km/hr • Additional sources of energy are: – Daily rotational motions of Earth on axis – Monthly rotational motions of Earth-Moon system about center of gravity How We Understand the Earth • Must think in terms of geologic time rather than human time – thousands, millions and billions of years • In 1788, Hutton introduced concept of geologic time: – “No vestige of a beginning, no prospect of an end.” – Everyday changes over millions of years add up to major results • Uniformitarianism: natural laws are uniform through time and space; present is the key to the past • Contrast to previously believed catastrophism • Currently modified actualism: rates of Earth processes can vary End of Chapter 2