stasz85: equinox

we have equinox because in the earths rotation around the earth and with its axis tilted it allows the suns rays to directly hit a part of the hemisphere which causes seasons for us.

Plate Tectonics theory

PLATE TECTONICS THEORY

Plate tectonics are an intrinsic part of most major geologic features.
Plate collisions form mountain ranges. In front of those mountain ranges, foreland basins may form creating accommodation space for deposits of sedimentary rock to accumulate.
Subduction zones often create volcanic activity, which in turn builds islands, and often large mountain ranges with volcanic origins. Subduction zones also create deep oceanic trenches. Those volcanoes add huge amounts of material to continents, allowing continents to grow (another related answer here claimed plate tectonics do not build continents, which is not true). As plate tectonics move island arcs they eventually collide with continents, accreting large amounts of rock onto continents. Plate tectonics are continually building and destroying continents.
Obduction zones, where oceanic crust is forced up over continental crust also add to continental crust.
Spreading centers create both huge mountain ranges under the ocean, and also create rift basins where sediments can accumulate, often many miles deep, and where future oceans may enter as continents split apart.
Passive margins and movement of plates can often create areas of subsidence, allowing isostatic processes to lower continental crust below sea level and creating new basins where sediment accumulates.
Hot spots under oceanic crust create islands such as Hawaii. As plate tectonic processes move the plate over these hot spots (which are themselves a part of plate tectonics) new islands are built, leading to island chains that stretch out across many miles and have many millions of years of history.
Plate tectonics even affects climate and weathering rates. As the Himalayas were built by the collision of two major plates, the climate of the planet was changed and atmospheric circulation patterns have changed. As mountain ranges rise, they change the amount of rainfall both in front of and behind the mountain ranges, often creating rain shadows behind the mountain ranges where there are often deserts. Some of the driest places on earth have been created by this tectonic process. Likewise those mountain ranges often capture rainfall on one side of the range and across the top of the range, changing the weathering rate of the region, creating glaciers, and changing the valleys below those ranges. One only has to look at the tree line on a mountain range to realize how plate tectonics have changed the forest biomes. Pretty much every biome on the planet has been created and is greatly affected by plate tectonics.

Plate tectonics are even responsible for the development of many species. For example, there are different species in the Rocky Mountains than are present in the Sierra Nevada because those ranges are not connected in space and have formed at different times. Polar bears have evolved in the Arctic, isolated from the Antarctic by plate tectonics, and penguins have evolved in the Antarctic due to the same plate tectonic isolation. The species found in the jungles of the Amazon are quite different from the species found in Africa, and those species only evolved after Africa and South America were separated by plate tectonics.

www.freewebs.com/guitarshredder/

platetectonics.com

Both the measurements and simulations show that the hottest part of Earth's interior is the iron core. Part of the heat down there is actually left over from the fiery formation of Earth; part is from latent heat released by the freezing of liquid iron in the outer core onto the solid inner core, and part is (possibly) from the slow decay of naturally radioactive elements like uranium and potassium mixed in the core. The core heats the bottom of the rocky mantle. The hottest rock near the bottom of the mantle becomes slightly less dense than the somewhat cooler rock above it, so buoyancy forces try to push the hottest rocks upward. Although the rock in the mantle is solid, the pressures and heat are so great that the rock can deform slowly, like hot wax. So the hot rock creeps upward through the cooler rock. As the hot rock rises, cooler rock flows downward to take its place next to the core, where it is heated and becomes buoyant enough to rise again later. The rising hot rock comes in contact with cold rocks near the surface of Earth where it gives off its heat, cools, and sinks again. Most of the rock in the mantle moves in this broad cyclic flow, indicated by the arrows in the figure. This zone, where rock is soft enough to flow, is called the asthenosphere.
(This means of heat transport--the cyclical movement of hot and cold material--is called convection. You can see an example of this in your kitchen by heating a pan of water to what is called a "rolling boil": hot water from the bottom of the pan rises up the sides, flows to the center, and sinks to the bottom again.)
Occasionally, however, masses of hotter-than-normal rock rise independently of the broad flow, like bubbles through a flowing stream. These masses of very hot rock form rising columns with rounded tops, called plumes.

Way back in 1912 a scientist by the name of Alfred Wegener came up with a crazy idea. He noticed that all of the continents seemed to fit together like the pieces of a giant puzzle. He thought, "Maybe they were once all joined together in a single, giant landmass that broke up and drifted apart over time?” He decided to give this supercontinent a name and called it Pangea, meaning, "all lands". At the time he presented his idea to the scientific community it came to be known as continental drift theory. Wegener was unable to find solid evidence to support his theory, so the other scientists laughed him off as a crackpot. One of his suggestions for the cause of continental drift was that centrifugal force from the rotation of the earth caused the continents to slide into each other and move around on the surface. They all calculated that there wasn't enough force generated by the earth's rotation to cause shifting of the crust and nobody took him seriously. They were all convinced the earth was rock-solid and immovable.
Bibliography
www.ucmp.berkeley.edu/geology/tecmech.html

http://en.wikipedia.org/wiki/Plate_tectonics

http://bprc.osu.edu/education/rr/plate_tectonics/pangea_diagram.jpg

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Tuesday, September 22, 2009

equinox

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