The Lithosphere Living on Shaky Ground
The Lithosphere is the outer shell of the Earth including the crust and the upper mantle. It is composed of brittle rock. • The lithosphere is broken into the tectonic plates. The plates or chunks of crust, drift about on the magma in the mantle below. • They move only a few centimeters a year.
Definition • The lithosphere is a rigid structure that comprises the Earth’s crust and part of the upper mantle. • - Mountains, volcanoes, caves, hills, plains and more are located in or on the lithosphere. • - The lithosphere is constantly changing its appearance because of climate changes and human activity. • - It ranges between 70 and 150 km in depth.
Continental DRIFT • Alfred Wegener developed the idea of continental drift. • Continental drift: The continental drift theory is the theory that once all the continents were joined in a super-continent, which scientists call Pangaea. • He made many observations before he concluded that the continents were all once joined together. • - Fossils of animals that could not swim or fly were found on the west coast of Africa and on the South America. • - The shapes of both Africa and South America fit together like a jigsaw puzzle. • - Certain mountain chains had similar rock composition (he thought that they all once belonged to one large mountain chain)
Pangea & panthalassa • Pangea is the name given to the supercontinent that existed long ago. • Panthalassa is the name given to the ocean that Pangea was in (Pangea resembled an island in one big ocean).
Plate tectonics • Wilson, a Canadian geophysicist, developed the idea of plate tectonics. • Once scientists had discovered that the upper mantle, the asthenosphere, was composed of partially melted rock, Wilson realized that the continents could move because they were “floating” on a mud-like substance. • Plate tectonics: earth’s crust is divided into large rigid plates that move. • As the plated move on the upper mantle, they cause, among others, earthquakes, tsunamis, the formation of mountains and volcanoes.
Convection: how plates move • Plates move because of convection currents in magma, beneath the plates. • As the magma is heated when it is close to the core, it rises. It moves horizontally because new molten rock is pushing it. As it moves horizontally, it takes the plate on its surface with it. The magma will cool down and fall back to the core where it is heated again and rises – the cycle continues.
How do they move? • Plates can move: • Apart (divergent boundary) • Toward each other (convergent boundary/subduction or collision) • Against each other (transform boundary)
Pressure builds up • Compression of a tectonic plate
Volcanoes • A volcano is a rupture or a break in a planets crust where hot magma, ash, and gases are released. • Volcanoes are usually found where plates are diverging (going apart) or converging (coming together). • Before an eruption there are many small earthquakes because moving magma pushes the ground out of it’s way.
Convergent boundaries • Oceanic-continental convergence = SUBDUCTION • When an oceanic plate pushes into and subducts under a continental plate, the overriding continental plate is lifted up and a mountain range is created.
Convergent boundaries • Oceanic-oceanic convergence • When two oceanic plates converge one is usually subducted under the other and in the process a deep oceanic trench is formed.
Orogenesis: mountains • Mountains are either formed by the subduction of an oceanic plate under a continental plate or by the collision of two continental plates.
Eathquakes • When two plates move sideways against each other (at a transform plate boundary), there is a tremendous amount of friction which makes the movement jerky. The plates slip, then stick as the friction and pressure build up to incredible levels. When the pressure is released suddenly, and the plates suddenly jerk apart, this is an earthquake.
TSUNAMI • A tsunami is series of huge ocean waves caused by a rapid, large-scale disturbance of the sea water. Tsunamis are caused by earthquakes the seafloor. In deep water, tsunami waves are less than a meter high, but they can travel at speeds exceeding 800 kilometers per hour and can easily cross an entire ocean basin.
Humans & the lithosphere • How do humans affect the lithosphere? • -humans put carbon into the atmosphere • -logging has killed trees and stopped them from using the carbon • -land uses such as agriculture, livestock grazing, and draining swamps move carbon from the soil to the atmosphere.