Earth's Lithosphere

• The Earth's crust is like the skin of an apple. It is very thin in comparison to the other three layers.
• The crust is only about 3 to 5 miles thick under the oceans (oceanic crust) and about 25 miles thick under the continents (continental crust).
• The crust is composed of two different rocks: granite and basalt.
• The continental crust is mostly granite.
• The oceanic crust is basalt.
• Basalt is much denser than granite.
• Less dense continental plates ride on the denser oceanic plates.
• The mantle is the largest layer of the Earth (1800 miles thick – 2/3 of earth’s mass), it is hot (5100 to 3300 Fahrenheit), and the source of most magma.
• The uppermost part of the mantle is rigid, and together with the crust, forms the lithosphere.
• The middle part of the upper mantle is composed of very hot dense rock that flows like asphalt, and it is called – asthenosphere.
• The lower mantle is hot and dense.
• The crust and the uppermost layer of the mantle together make up a zone of rigid, brittle rock called the Lithosphere.
• The crust of the Earth is broken into many pieces called lithospheric or crustal plates.
• The plates float on the soft, semi-rigid or plastic asthenosphere.
• The asthenosphere is the semi-rigid part of the upper mantle that flows like hot asphalt under a heavy weight.
• The asthenosphere 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 – repeating this cycle over and over.
• When the convection currents flow in the asthenosphere they also move the lithospheric or crustal plates.
• The core of the Earth has a radius of 2100 miles and contains 1/3 of Earth’s mass.
• The core is like a ball of very hot metals, with estimated temperatures of 12,400 Fahrenheit at the center, and 8,600 Fahrenheit at the outer limits.
• The outer core (~1400 miles thick) is so hot that metals in it are in liquid state. It is composed of mainly melted nickel and iron. The Earth’s magnetic sphere is largely related to this.
• The inner core of the Earth, about ~700 miles thick, has temperatures and pressures so great that the metals are squeezed together and are not able to move about like a liquid, but are forced to vibrate in place like a solid.
• Density of materials (rocks, minerals) greatest in the center (core), and decreases towards the surface
• Gravitational force strongest at the center, decreasing towards the surface (Newton’s Universal Law of Gravitation)
• Temperature also decreases from center to the periphery
• Pressure decreases from center to periphery as well
• Layers in earth’s internal structure are differentiated by composition, density, temperature and other characteristics
• Earth’s interior is an immense reservoir of minerals and geothermal energy
• The Earth is composed of a number of different layers as determined by deep drilling and seismic evidence.