Earth’s Interior A RGHYA G OSWAMI (R AJ ), P OSTDOC
Is Earth a Sphere? The Earth is only approximately spherical, so no single value serves as its natural radius. Distances from points on the surface to the center range from 6,353 km to 6,384 km (3,947– 3,968 miles). The average distance from Earth's center to its surface, about 6,371 kilometers (3,959 miles).
Earth ’ s internal structure (Based on Physical Propeties) Atmosphere A layer of gases, retained by Earth's gravity Has a mass of about 5.15×10 18 kg, three quarters of which is within about 11 km (6.8 miles). The Kármán line, at 100 km (62 miles), or 1.57% of Earth's radius, is often used as the border between the atmosphere and outer space. Hydrosphere Discontinuous layer of water at or near the Earth’s surface Includes all liquid and frozen surface waters, groundwater held in soil and rock, and atmospheric water vapor. It holds about 1.4 billion cubic kilometers (326 million cubic miles) of water (mass is about 1.4 × 1018 tonnes, which is about 0.023% of the Earth's total mass) Geosphere The geosphere is considered the portion of the Earth system that includes the Earth's interior, rocks and minerals, landforms Earth Science (12 th Edition) Tarbuck, Lutgens, Tasa
What is Earth’s Interior Like? Earth scientists study the bending/refraction and reflection of seismic waves (P and S waves) to understand Earth's interior. Earth Science (12 th Edition) Tarbuck, Lutgens, Tasa The Changing Earth (6 th Edition) by Monroe & Wicander
Views of Earth’s layered structure Earth Science (12 th Edition) Tarbuck, Lutgens, Tasa
Earth ’ s internal structure Inner Core Sphere with a radius of 1,216 km (754 miles) Behaves like a solid. Temperature of surface of the Sun (5700 K or 5430C), pressure is 330 to 360 gigapascals (3,300,000 to 3,600,000 atm) Composed of an iron–nickel alloy, average density of nearly 12.8 ~ 13.1 g/cm 3 Outer Core Below mantle, liquid layer A sphere having a radius of 3,486 km (2,161 miles), 2,270 km (1,410 miles) thick Composed of an iron–nickel alloy, average density of nearly 11 g/cm3 Convective flow of metallic iron within generates Earth’s magnetic field Temperature ranges from 4,300 K (4,030C; 7,280°F) in the outer regions to 6,000 K (5,730°C; 10,340°F) Earth Science (12 th Edition) Tarbuck, Lutgens, Tasa
Earth ’ s internal structure Mantle Below crust to a depth of 2,900 kilometers (1,800 miles) Composition of the uppermost mantle is the igneous rock peridotite (changes at greater depths) Temperatures range between 500 ~ 900°C (932 to 1,652 °F) at the upper boundary with the crust; to over 4,000 °C (7,230 °F) at the boundary with the core. Crust Thin, rocky outer layer Varies in thickness Roughly 7 km (5 miles) in oceanic regions Continental crust averages 35–40 km (25 miles) Exceeds 70 km (40 miles) in some mountainous regions Earth Science (12 th Edition) Tarbuck, Lutgens, Tasa
Earth ’ s internal structure Continental crust crust composed of felsic granitic rocks, rich in silica and aluminum (also called SiAl) Upper crust is more granitic Lower crust is more akin to basalt Average density is about 2.7 g/cm 3 Up to 4 billion years old Oceanic Crust Composed of mafic rocks (basaltic composition) rich in silica and magnesium (also called SiMa) Density about 3.0 g/cm 3 Younger (180 million years or less) than the continental crust Earth Science (12 th Edition) Tarbuck, Lutgens, Tasa
Earth ’ s internal structure (Based on Physical Propeties) Lithosphere Crust and uppermost mantle (about 100 km thick) Cool, rigid, solid (Plate) Asthenosphere Beneath the lithosphere Upper mantle To a depth of about 660 kilometers Soft, weak layer that is easily deformed Mesosphere (or lower mantle) 660–2,900 km More rigid layer Rocks are very hot and capable of gradual flow Earth Science (12 th Edition) Tarbuck, Lutgens, Tasa
o Boundaries between the layers are called discontinuities. Mohorovičić discontinuity (Moho) between crust and mantle Gutenberg discontinuity between mantle and core Earth ’ s internal structure Earth Through Time (9 th Edition) Harold Levin