Presentation on theme: "Chapter 17 Earth’s interior. Earth’s interior structure Earth is composed of three shells; –Crust –Mantle –Core."— Presentation transcript:
Chapter 17 Earth’s interior
Earth’s interior structure Earth is composed of three shells; –Crust –Mantle –Core
Earths interior and seismic waves The study of earth’s interior can be done by; –Direct sampling –Indirect methods
Meteorites Seismic waves (P and S) P-waves can pass through all materials (solids and fluids) S-waves can only pass through solids.
The crust Outermost layer of the earth forming a thin skin. Divided into 2 parts;Outermost layer of the earth forming a thin skin. Divided into 2 parts; –Continental crust –Oceanic crust
Continental crust: –10-70 km thick, thickest beneath Himalayas. –Density 2.7 g/cc –0.374% of Earth's mass. –Consists of (felsic) granitic rocks below and sed. Rocks above. –Seismic wave velocity is 6 km/sec.
Oceanic crust: –5-8 km thick. –Density 3 g/cc –0.099% of Earth's mass –Consists of mafic rocks (basalt and gabbro). –Seismic wave velocity is 7 km/sec.
Mantle: –upper mantle and –lower mantle Upper mantle and crust constitute Lithosphere where the rocks are in rigid form.
Lower mantle is also called Asthenosphere where the rocks are in plastic state.
The boundary between the crust and mantle is called the Moho.
The mantle: –67% of Earth's mass –Density 3.3 g/cc –depth of kilometers. –Consists of olivine, pyroxene and garnet –Seismic wave velocity is 8 km/sec. The boundary between the crust and mantle is called the Moho.
The Core Is there really a core? –Combined Density of the crust and mantle is less than that of the whole earth. –S-waves shadow zone
The Core Core is divided into 2 parts; –The outer core is about 2,250 km thick, composed of molten iron and nickel. –The inner core is probably solid iron and nickel at about 5000° C.
What is isostasy? It’s a balance or equilibrium of the earth’s crust floating on the dense mantle. Can be compared with wooden blocks floating on water. The higher the wood block appears, the deeper its root.
Erosion of continental crust shows isostatic equilibrium.
Erosion of glacial ice shows isostatic equilibrium in the form of crustal rebound.
Physical properties of Earth Gravity Magnetism Heat flow
Gravity: gravitational attraction exists among all bodies in the universe
Gravity meter is used to measure gravity.
Gravity anomalies: abnormal gravity readings. –Positive anomaly: gravity reading higher than the regional gravity readings –Negative anomaly: gravity readings lower than the regional gravity readings
Magnetism: the earth acts like a giant dipolar magnet. Magnetic poles: oriented 11.5° from the geographic poles. –North pole –South pole Magnetometer is used to measure magnetic strength.
Source of magnetism the convection currents in outer liquid core produce electric currents and any electric field is associated with a magnetic field.
Normal and reversed polarity
Paleomagnetism: the study of ancient magnetism preserved in rocks.
Magnetic anomalies –Positive –Negative
Heat flow: the rate at which temperature increases within the earth is called Geothermal gradient. 25° C/km at shallow depths (crust) but drops to 1°C/km within the mantle.
Sources of heat inside the earth: –Radioactivity –Rising magma bodies –Gravitational energy from accretion.