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Transcript
Earth’s Layers The Structure of the Earth Layers of the Earth • The layers of the Earth in order from the center out are. – Inner core – Outer core – Mantle • lower • Middle • upper – Asthenosphere – Lithosphere (crust) The Crust • The crust is the outermost layer of the Earth • Most widely studied and understood • Made up primarily of silicon and oxygen • Very thin when compared to the other layers – 3-5 miles or 8 km thick under the oceanic crust – 32 km or 25miles thick under the continental crust The Crust • The crust is the thinnest layer of the earth. – Oceanic crust • The mantle is the thickest layer of the Earth – Stretches from the lithosphere to the outer core Continental Crust • Composed mainly of granite • Thicker than oceanic crust (30-50 km) • Makes up only 25% of Earth’s surface • Less dense than oceanic crust Oceanic Crust • Oceanic crust is composed of primarily basalt • Basalt is much denser than the granite. – The less dense continents ride on the denser oceanic plates • Covered by water • Makes up 75% of Earth’s crust. • Thinner than the continental crust (5-10km) The Lithosphere • The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the lithosphere. Lithospheric Plates • The crust of the Earth is broken into many pieces called (lithospheric) plate. • The plates “float” on the soft, semi rigid asthenosphere Mohorovicic Discontinuity • The imaginary line of discontinuity that separates the brittle crust of the earth from the mantle is the Mohorovicic Discontinuity or MOHO for short. • Boundary between the crust and the mantle in the earth. • Depth where seismic waves change velocity and there is also a change in chemical composition MOHO The Mantle • The mantle is the thickest layer of Earth. • 2,885 km thick, the mantle is 82% of Earth’s volume. – Upper mantle – Middle mantle • Asthenosphere – Lower mantle • Mesosphere (middle layer) • Mantle composition is an ultramafic rock called peridotite. • Solid rock layer between the crust and the core. The Upper Mantle • The uppermost mantle is connected to the crust and forms the asthenosphere, which composes Earth's tectonic plates. • Part of the lithosphere The Asthenosphere Middle Mantle • The asthenosphere is the semi-rigid part of the middle mantle that flows like hot asphalt under a heavy weight • The movement of the middle mantle, asthenosphere, is the reason that the crustal plates of the Earth move. Convection Currents • The middle mantle "flows" because of convection currents. • Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again • The cycle repeats over and over. • The molten rock below Earth’s surface is known as magma The Lower Mantle • Called the Mesosphere because it is the middle layer of Earth. – “middle” sphere • 2,250 km thick • lowest part of mantle The Outer Core • 1400 miles thick • It is so hot that the metals in it are all in the liquid state. • Composed of the melted metals of nickel and iron. • The flow of the inner core creates Earth’s magnetic field Earth’s Magnetic Field • The flow of the fluid outer core around the solid inner core creates the Earth’s magnetic field The Inner Core • The inner core of the Earth has extremely high temperatures and pressures – 4,000 - 5,000 °C – 3 million atmospheres • Pressure is so great that the metals are squeezed together and are not able. – forced to vibrate in place like a solid. – A ball of very hot metals. • Inner core dimensions – 3,248 km radius • Composed of a sphere of hot, dense nickel and iron • 1/3 of the Earth’s mass Proof of Earth’s Structure • Seismic Waves: the waves that travel through the Earth’s interior during an earthquake. • Altered by the type of material that it travels through. • Timing and strength of seismic waves gives us a picture of Earth’s interior Using the diagram which seismic wave travels through what type of substance? Seismic Waves • P-Waves – Travels through any substance – Compression wave – Any substance can be compressed – Solid, liquid, gas • S-Waves – Transverse, shear waves – Travels through solid only Seismic Shadow Zone • 104 -140 degrees from the epicenter – No direct P-waves – S-Waves are stopped entirely by the liquid core – P-Waves are bent Think, Pair, Share • Write down the following question on a sheet of paper. – Have we ever seen part of the Mantle? Explain. – Include an illustration of the explanation. • Discuss the question with your partner and write the answer down. • Sit quietly until I say time is up