Plate tectonics It was first truly understood that the plates of the Earth move across the planet&rs

Plate tectonicsIt was first truly understood that the plates of the Earth move across the planet’s surface in the 1960s. The evidence at the time was tectonic –faults and mountain ranges on the ocean floor, and magnetic – stripes parallel to the ocean ridges formed in the presence of a magnetic field that occasionally flips which direction it points.Today, we have new ways of measuring the motion of the Earth’s surface. Lasers can measure the distance between two points with impressive accuracy and radar techniques can see how rock positions change with time. Beyond those though is a tool many of us use every day just to get around: the Global Positioning System.GPS satellites were placed around the earth in the early 1990s. Once the network was fully deployed, a single station placed on the surface of the Earth could be used to measure how much a plate moved relative to a fixed coordinate system established by the satellites.These arrows reflect the actual measured yearly motion of GPS receivers on the planet’s surface. Because all of the plates on Earth’s surface move relative to one another, making a plot like this requires choosing a reference frame, a point that all other motions are expressed relative to. In this case, that point is on the continent of Antarctica, which is why the stations at the edge of that continent only barely move.The Pacific plate screams to the northwest at a velocity approaching 10 cm/year before reaching subduction zones off the coast of Japan and Asia. North America is moving to the west but with a slight rotational component relative to Antarctica. Europe and Asia are moving to the northeast, but the continent is being bent and deformed by the impact of India on its southern coast.Major faults and plate boundaries are also marked by major changes in plate motion direction. For comparison, human fingernails grow at about 3 mm/month, 3.6 centimeters per year. The speeds of plate motion are therefore just slightly faster in most cases than the growth rate of your fingernails.-JBBImage credit: http://commons.wikimedia.org/wiki/File:Global_plate_motion.jpgRead more: http://www.jclahr.com/science/earth_science/thumbnail/index.htmlhttp://bit.ly/1CDuNGV -- source link

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