Plate Tectonics Newsela 2-4-21

 The lithosphere is the solid, outer part of the Earth. It includes the brittle upper portion of the mantle and the crust, the planet's outermost layers. The lithosphere is located below the atmosphere and above the asthenosphere. The asthenosphere is made of melted rock that gives it a thick, sticky consistency. It acts much more like a liquid than the lithosphere. The lithosphereasthenosphere boundary (LAB) is the point where the lithosphere changes to the asthenosphere. The depth of the LAB is not fixed, but varies by region.

There are two types of lithosphere: oceanic lithosphere and continental lithosphere. Oceanic lithosphere is slightly denser and is associated with oceanic crust, which makes up the sea floor.

The lithosphere is divided into huge slabs called tectonic plates. There are eight major plates and several smaller plates, including the North American, Caribbean, South American, Scotia, Antarctic, Eurasian, Arabian, African, Indian, Philippine, Australian, Pacific, Juan de Fuca, Cocos, and Nazca plates. The heat from the mantle makes the rocks at the bottom of the lithosphere slightly elastic, which allows the plates to move. The movement of these plates is known as plate tectonics. Most tectonic activity takes place at the boundaries of these plates, where they may collide, tear apart, or slide against each other.

 Tectonic activity is responsible for some of Earth's most dramatic geologic events. It is what forms earthquakes, volcanoes, mountain ranges and deep ocean trenches. Both oceanic and continental lithospheres are thinnest at rift valleys and ocean ridges, where tectonic plates are shifting apart from one another. The Lithosphere And Other Spheres The solid rock of the lithosphere is one of five systems that shape the planet. Other "spheres" include the biosphere (living things), the cryosphere (ice and frozen soil), the hydrosphere (liquid water) and the atmosphere (the air surrounding the planet). 

Together, these spheres influence all of the natural world. For example, it takes a combination of the systems to create the pedosphere, or the part of the lithosphere made of soil and dirt. Hard rocks of the lithosphere might be ground down to powder by the powerful movement of an icy glacier. Weathering and erosion caused by wind or rain can also wear down rocks. Plant and animal remains from the biosphere mix with these eroded rocks to create fertile soil, which is the pedosphere. The interaction of these systems influences every environment on Earth. Tall mountains, for example, often have lower temperatures than valleys or hills. In high-altitude mountain ranges, the lithosphere interacts with the thinner air and precipitation to create a cool or even icy climate zone. 

 Over time, plants and animals have adapted to life in these unique environments. Fast Facts: The LAB The depth of the lithosphere-asthenosphere boundary (LAB) is a hot topic among geologists. They use the temperature and consistency of the mantle to determine the position of the LAB. What they have found varies widely. There is a thinner, crust-deep boundary under ocean ridges, but under some landforms the lithosphere can extend for 124 miles (200 kilometers). Extraterrestrial Lithospheres All terrestrial planets have lithospheres, but they are not all identical. The lithospheres of Mercury, Venus and Mars are much thicker and more rigid than Earth's lithosphere.