Consequences of a “dynamic” Earth Earthquakes Volcanoes Mountain Building
Energy Sources for Natural Disasters 1. Gravity The planet Earth generates a pull on every other object in the entire universe! It is this pull that creates weight. It is this pull that causes an object to fall. Such a pull is called a force. The force that causes an object to fall is the force due to gravity. Gravity on the earth is constant... All objects fall equally fast. If we think about this and take it a bit further we come to the realization that the force of gravity is what causes the acceleration due to gravity. The gravitational acceleration of the Earth (9.8 m/s 2 )
Gravity and Newton’s Law F = ma (or F=mg) A force applied to an object causes an acceleration in that object. The force of gravity is what causes the acceleration due to gravity. (9.8m/s) The more material an object has or the greater its mass, the greater the force that pulls on it. The net force acting on an object is equal to the product of the object's mass and its acceleration. Consider free fall of an object due to gravity. The force of gravity is proportional to mass m, so we can write F = mg, where g is the acceleration of gravity, directed downwards..
Energy Sources for Natural Disasters 1. Gravity - 2. Earth’s Internal Heat
Internal Sources of Energy Three Sources of the Earth’s Internal Energy (Heat) 1.Impacts of asteroids 2.Decay of radioactive elements 3.Gravitational contraction
Origin of the Solar System Rotating cloud of dust and gas gathers due to gravitational forces. Rotating mass contracts and flattens with most of the mass in the center. A B C Planets form by the accretion of stony and iron meteorites as well as ice particles. D Star ignites to form the sun. Gases blown to outer planets.
Differentiation of the Earth……. produces Earths’ internal structure Crust, Mantle and Core
Radius = 6370 km Distance to Core is ~1/2 the radius (2900 km depth)
Earth Structure The earth today is the product of over 4.5 billion years of differentiation into layers of varying density. The 8 most abundant elements in the earth are iron (Fe), oxygen (O), silicon (Si), magnesium (Mg), sodium (Na), calcium (Ca), aluminum (Al) and potassium (K),
Earth Structure - Density Stratified Layers Earth’s Core The earth’s core is composed of two parts, the inner core and the outer core. The inner core is SOLID iron (Fe) and nickel (Ni) and the outer core is LIQUID Fe and Ni.
Earth Structure - Density Stratified Layers Mantle Chemically the mantle is composed of Fe, Mg, Si and O. (ULTRAMAFIC composed of Fe, Mg silicates) The mantle extends from roughly 50- 2900km below the earth’s surface.
Earth Structure - Density Stratified Layers Crust Is composed of two types: Oceanic Crust (below ocean) which is 7-10 km thick also made of Si, O, Fe and Mg. (MAFIC composed of Ca, Fe, Mg silicates) Continental Crust which is 20-70km thick made of Si, O, Fe and Mg. (FELSIC composed of Ca, Na, K silicates)
Earth Structure - Density Stratified Layers Crust vs. Mantle The mantle contains MORE Fe and Mg than the oceanic crust and the oceanic crust contains MORE Fe and Mg than the continental crust. Because Fe and Mg are DENSER elements, the mantle is denser than the oceanic crust and the oceanic crust is denser than the continental crust. Assume the two blocks to the left are of equal volume and they are composed of the same material (red atoms). If density=mass/volume which box has the higher density? Density can also vary from element to element
Earth Structure - Layers of Different Strengths The earth is layered with respect to physical properties. The crust and the upper part of the mantle is called the LITHOSPHERE and it is RIGID, BRITTLE and behaves ELASTICALLY. The part of the mantle directly below the lithosphere is termed the ASTHENOSPHERE which behaves like a PLASTIC - a solid that flows.
Moho Continental Oceanic Upper Mantle and Crustal Structure Lithosphere (or plate) = crust + uppermost, rigid part of the mantle
Natural Disasters Earth’s Internal Structure Introduction to Plate Tectonics Earth’s Energy Sources and Systems
Plate Tectonic Theory 6 large plates (e.g., Pacific Plate) 7-10 small plates (e.g., Arabian Plate)
Mantle Convection Drives Plate Motion internal heat engine Heat Sources Original heat from formation of the Earth Radioactive decay of U, Th, and K in the core and mantle