Earth’s Structure Earth’s Structure
Earth consists of a series of concentric Divisions of the Earth based upon layers or spheres which differ in physical state are the Lithosphere, chemistry and physical properties. Asthenosphere, Mesosphere, Outer The compositional layers of the Earth, core, and Inner core. differentiated by their chemistry, are The Lithosphere is rigid, or brittle, the Crust, the Mantle, and the Core. and consists of the crust and The Core is subdivided into a molten uppermost mantle. outer core and solid inner core. The Aesthenosphere is ductile, or Three spheres surround the rocky plastic, and can flow. portion of the Earth. The Mesosphere is a more rigid Hydrosphere includes all of the zone of the mantle. “free” water of the Earth contained The Outer Core is liquid, and the in the ocean, lakes, rivers, snow, ice, Inner Core is solid, as increased water vapor and groundwater. pressure in the inner core raises Atmosphere is the gaseous envelope the melting point temperature. that surrounds the Earth and is mainly a mixture of nitrogen and The layers are arranged in order of oxygen. increasing density, from the Crust Biosphere refers to all living and to the Core. This is known as non-living organic matter. density stratification.
Density Density Stratification
Luke, What is density? How did Earth’s layers form? embrace your density ! Defined as mass per About 5 billion years ago … Oh, wait … unit volume Solar system (Sun and planets) began to form from Determines what solar nebula, including “Proto-Earth” floats on top (less Nebular material (gas and dust) in Proto-Earth was dense), sinks to very uniform, no stratification bottom (more dense) As Earth began to cool and coalesce, heavier Delineates the inner materials, such as iron and nickel, migrated toward layers of Earth center ρ Denoted by rho ( ) Lighter materials, such as silicon, oxygen, aluminum, Delicious! and potassium remained near the surface
1 Origin of Oceans Two types of crust About 4 billion years ago … oceanic vs. continental 1. Outgassing Volcanic activity released low- density gases from interior Mostly water vapor, carbon dioxide, hydrogen, others
2. Condensation into gaseous clouds
3. Formation of early atmosphere and oceans Atmosphere devoid of oxygen Oceans’ chemistry different from today’s oceans
Continental Margin
continental shelf Ocean Basin continental slope shoreline sea level continental rise 0 (with thick wedge of sediment 0 4 km abyssal plain at base of slope) Oceanic Crust Continental 25 km 7 km (2.9 g/cm 3 ) Crust 3 Isostasy 10 Moho (2.7 g/cm ) 10
transition from Two types of crust continental crust to oceanic crust the ductile (or plastic ) 20 Moho 20 Asthenosphere supports the this column of Oceanic Crust Continental Crust rigid Lithosphere 30 30 continental lithosphere thin, more dens e thick, les s dens e condition of equilibrium is • composed of dark-colored mafic • composed of light-colored felsic maintained between crustal 40 is in equilibrium with40 rocks like bas alt (rich in Mg, Fe ) rocks like granite (rich in S i, Al) blocks of different thickness 3 3 • avg. density: 2.9-3.0 g/c m • avg. density: 2.7-2.8 g/c m and density 50 uppermost Mantle 50 (3.3 g/cm )3 • thickness: 4-10 km • thickness: 30-40 km 89 km 76 km the Asthenosphere and forms ocean basins "buoyant" continents stand high Lithosphere can accommodate 60 60 s ubducted at trenches during pre fere ntially pres e rved during changes in the redistribution of collision collision load (ice sheets, volcanoes, 70 70 ocean basins <200 million years old continents >3500 million years old (i.e., the present ocean basins (i.e., the continents are old) mountains, erosion) this column of 80 80 are relatively young features) the Lithosphere is in isostatic oceanic lithosphere equilibrium with the underlying Asthenosphere, meaning that 90 90 the pressure at point A is equal 100 base of Lithosphere 100 to the pressure at point B. ABAsthenosphere
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