As the earth rotates the outer core circulates around the inter core witch cause a

TBecause the outer core moves around the inner core, Earth's magnetism is created.he Outer Core is the second to last layer of the Earth.  It is a magma like liquid layer that surrounds the Inner Core and creates Earth's magnetic field. The Outer Core is about 4000-5000 degrees Celsius. The Inner Core is so hot it causes all the metal in the Outer Core to melt into liquid magma. The Outer Core is composed of iron and some nickel.  There is very few rocks and iron and nickel ore left in the Outer Core because of the Inner Core melting all the metal into liquid magma.The Outer Core is about 2200 km thick.  It is the second largest layer and made entirely out of liquid magma. 
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The changes to agriculture in the united states since 1900 is that increased mechanization has increased food production, thereby increasing the need for labor. there has been an increased need for higher speeds of food production due the fact that the population in the united states continues to rise.