The lithosphere, which is the rigid outermost shell of a planet (the crust and upper mantle), is broken up into tectonic plates. The Earth's lithosphere is composed of seven or eight major plates (depending on how they are defined) and many minor plates. Where the plates meet, their relative motion determines the type of boundary: convergent, divergent, or transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries. The relative movement of the plates typically ranges from zero to 100 mm annually.[2]
Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries, subduction carries plates into the mantle; the material lost is roughly balanced by the formation of new (oceanic) crust along divergent margins by seafloor spreading. In this way, the total surface of the lithosphere remains the same. This prediction of plate tectonics is also referred to as the conveyor belt principle. Earlier theories, since disproven, proposed gradual shrinking (contraction) or gradual expansion of the globe.[3]
Tectonic plates are able to move because the Earth's lithosphere has greater strength than the underlying asthenosphere. Lateral density variations in the mantle result in convection. Plate movement is thought to be driven by a combination of the motion of the seafloor away from the spreading ridge (due to variations in topography and density of the crust, which result in differences in gravitational forces) and drag, with downward suction, at the subduction zones. Another explanation lies in the different forces generated by tidal forces of the Sun and Moon. The relative importance of each of these factors and their relationship to each other is unclear, and still the subject of much debate.
Answer:
A: declare sovereignty in a document,such as the Declaration of Independence.
Explanation:
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Saturn is predominately composed of hydrogen and helium, yet doesn't undergo fusion like the Sun due to the lacking mass.
<span>The correct answer is (D), sheep. Didgeridoos and boomerangs are artifacts invented by humans in Australia. Koalas evolved in Australia, and to this day are only found in the wild in Australia. In contrast, sheep were first domesticated in ancient Mesopotamia and then brought by humans to other parts of the world. The first sheep were brought to Australia by ship, from the Cape of Good Hope in 1788.</span>
Answer:
The Fertile Crescent was good for farming because of the fertility of its land, a result of irrigation from numerous large rivers in the region.
Advantages:
Irrigation and agriculture developed here because of the fertile soil found near these rivers. Access to water helped with farming and trade routes. Soon, its natural riches brought travelers in and out of the Fertile Crescent.
Disadvantages:
Since the world's earliest civilizations developed in the Fertile Crescent, it is not hard to imagine that there are many geographical advantages. The presence of two rivers and the sediment they leave behind after flooding made for successful crop surpluses. But the Tigris and Euphrates Rivers were also a disadvantage..
