Earth's Internal Structure PDF

EARTH'S INTERNAL STRUCTURE Earth's Differentiation Differentiation = segregated into a series of concentric layers of differing composition and density Molten iron and nickel sank to form the core Lighter silicates flowed up to form mantle and crust Distinct Layers Compositional Layers...

EARTH'S INTERNAL STRUCTURE Earth's Differentiation Differentiation = segregated into a series of concentric layers of differing composition and density Molten iron and nickel sank to form the core Lighter silicates flowed up to form mantle and crust Distinct Layers Compositional Layers \- Based on material or chemical composition Crust Mantle Core Mechanical Layers \- Based on temperature and the ability of seismic waves to penetrate Earth's interior - Lithosphere - Asthenosphere - Lower Mantle/Mesosphere - Outer Core - Inner Core Crust - The outermost layer of the Earth - Oxygen is the most common element in the crust! - Oxygen bonds with the other elements to make minerals of the crust. The crust is not just oxygen! - 2 types: - Continental Crust 20km \~ 90km thick (12\~56miles) - Density of 2.7g/cm3 (less dense, therefore floats over oceanic crust) - Made up of granite and andesite rocks - Continental crust is made up of all rock types. - In general it is where you find less dense minerals - More pores (spaces) in the rocks further decrease density - Oceanic Crust 5km \~ 10km thick (3\~6miles) - Density of 3g/cm3 - Consist primarily of basalt rock - Oceanic crust made of more dense rocks. - The minerals have a higher amounts of iron and magnesium - Smaller pores means higher density Mantle - Layer beneath the crust - Mantle is about 2,900 km thick! About 1800miles. - Contributes to 67% of the total mass of Earth. - The mantle is SOLID ROCK, it is not a liquid! - Has a density from about 3.5g/cm3 to 5.5g/cm3 - The material is similar to that of ultramafic rock called peridotite which is made of iron and magnesium. - But, if the mantle is SOLID how can it flow? - At about 100km -- 150km it is hot enough to flow very slowly. - Its temperature is hot due to the transfer of heat that takes place from the core. - Heat flows outside through the process of conduction and convection. - Conduction is when the heat coming from the core travel through atoms by rapid collision with one another - Convection is caused by heat currents that allow materials to flow and move freely Core - The inner part of the Earth - The core is made up of iron and nickel alloy (iron mixed with small amounts of other elements) - Makes up 31% of Earth's composition - Source of internal heat - Outer core is about 2255km thick. About 1400miles - Outer core is liquid because temperature is so high that not even the high pressure can force it to become solid. - Inner core is about 1220km thick. About 758miles. - Even though it is hotter than the outer core, the pressure is so high that the atoms get forced together to make a solid. - The swirling convective flow in the outer core creates earth's magnetic field. - The core actually spins slightly faster than the rest of the planet due to the force of earth's magnetic field. Mechanical Layer: Lithosphere and Asthenosphere - So far, we have broken the layers down by composition and density. (Crust, Mantle, Core) - We can also divide them up by how they "behave" - The upper most layer is called the lithosphere - It is rigid, meaning it can bend slightly but not flow at all. - This layer extends down from the surface about 100-150km. Lithosphere and Asthenosphere - Below the lithosphere you have the asthenosphere - The asthenosphere is entirely upper mantle rock - It is NOT A LIQUID! - But it is hot enough, 1280°C or 2330°F, that it can flow very slowly. - Even at that temp. it can only flow about 10cm -- 15cm per year Earth's Interior Layers Lithosphere - solid upper mantle and crust - broken into plates that move over the asthenosphere Asthenosphere - part of upper mantle - behaves plastically and slowly flows Plate Tectonic Theory - Lithosphere is broken into individual pieces or plates - Plates move over the asthenosphere as a result of underlying convection cells Lower Mantle - Region of increased pressure - The lowest part of mantle, next to outer core Outer Core - External Part of the core - This region is liquid and composed mainly of an iron-nickel alloy - The temperature is so high that it reaches about 4000-5000°C - Responsible for the magnetic field generation of Earth Inner Core - The internal part of the core - Made up of very dense and heavy iron and nickel material which does not melt easily at very high temperatures Boundaries and Seismic Discontinuities - Seismic discontinuity is the quick change in seismic velocities in a boundary Mohorovičić Discontinuity - Boundary between the crust and the mantle - Named after the Croatian seismologist Andrija Mohorovičić in 1909 - Andrija found out that seismic waves abruptly change from a constant difference at a distance greater than 200 km from epicenter. In his findings he found out that there is a boundary between two layers of Earth's Interior. - Moho has an average depth of around 8 km under the ocean basin and around 32 km under the continental crust Gutenberg Discontinuity - The boundary at which the mantle meets the core - Discovered by the German --born American seismologist Beno Gutenberg - Beno found out that at some depth, the P- wave slows down and hinders the movement of S-wave. It proves that S- wave cannot travel through liquid regions. This resulted in the idea that core is made up of molten materials because it does not allow the S-wave to penetrate in it. Lehmann Discontinuity - The region between the inner and outer core - Named after Inge Lehmann a Danish seismologist and Geophysicist - Her discovery is a breakthrough in the study of Earth's interior. She explained that based on the analysis of seismic wave measurements, the core is made up of molten region and a solid region.