Looking at pictures of our planet earth from space might leave one with the impression that it is one giant solid ball of rock.
However, scientists using very sophisticated and sensitive equipment, give us a much different picture.
Only a very thin shell, called the crust, is completely solid. It is made of rock that can be very thick, but is on the average about 25 miles thick under the continents and only about 4.3 miles thick beneath the oceans.
Beneath the crust, is a layer called the mantle that is some 1,900 miles thick and composed of warm rock that continuously flows extremely slowly like thick molasses.
Beneath this layer is an outer core composed of molten metal that is mostly iron with a little nickel. This layer is molten metal due to the extremely hot temperatures that result from continuous atomic reactions.
As one looks deeper towards the center, the temperature can reach a toasty 11,000 degrees Fahrenheit, which is hotter that the surface of the sun. The inner core is extremely hot, but composed mostly of solid metal due to the tremendous pressure it is under.
The earth's rocky crust is broken up into a patchwork of approximately 20 large pieces called tectonic plates. These plates slowly split apart, drift, and collide as they are carried about on the surface very slowly by the activity of the soft mantle. This movement is called continental drift, and is responsible for earthquakes and volcanoes where the plates meet, as well as our magnificent mountain ranges where the plates crunch into one another which lifts the crust up into mountain ranges.
The movement is very slow, but over long periods of time can produce huge changes in the surface configuration of the continents. For example, some 220 million years ago the present day continents were all joined together as a single land mass called Pangea. Slowly the plates carrying the various continents separated and moved about to produce the features of the earth that we observe today.
Each year, North America is still drifting away from Europe at a rate of three-fourths of an inch, making the Atlantic Ocean wider, while the Pacific Ocean is shrinking. The distance moved each year doesn't sound like much to those of us who think in terms of decades rather than millions of years, but over time it can have huge implications.
It is interesting to note that the area where New York is now located was once on the equator. Also, the Himalayan Mountains are getting higher because the Indian Plate is still pushing into the Asian Plate that started their formation.
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