The Interior of the EarthBy Moira Whitehouse PhD
The surface of the Earth is constantlychanging as new landforms are builtand older ones are destroyed by theforces of the Earth.
Some changes happen so slowly thatyou do not see the differences for along time—for example the Coloradoriver carving the Grand Canyon hasbeen happening for millions of years.On the other hand, volcanic eruptions andearthquakes can change the surface of theEarth very quickly.
How are Landforms Made?• Now let’s examine the forces thatcreate the different landforms. Broadlyspeaking, there are two kinds:•Constructive forces—those that build up theland.• Destructive forces—those that wear downthe land.
To understand the constructive forces ofthe Earth—the ones that build uplandforms, we need to understand whatthe interior (the inside) of the Earth islike.
The thin, outermost layer of the earth ismade of solid rock and is called the crust.All of the landforms on Earth are located Cruston the crust and all life on Earth exists onthis top layer.
The Earth’s crust consists of the oceanic andthe continental crusts, both of which float onthe magma (melted rock). • The oceanic crust is the layer of rock which forms the floor of an ocean. It is about 4-7 miles thick. • The continental crust is the layer of rock which forms the continents and those areas magma of shallow seabed close to the shore. The continental crust is much thicker than the oceanic crust--about 19 miles thick.
The continental crust is mainly made of arock called granite.The oceanic crust is made of mostlybasalt, a very dense rock that is muchheavier than the granite of the continentalcrust.As a result, the oceanic crust sinks deeperinto the magma (the molten rock) whenthe continental and oceanic crust meet.
This rockis mainlygranite. This rock magma is mainly basalt.
The mantle is the layer directly below thecrust. NASA image• It is about 1800 miles thick and made ofmelted rock.
As you get closer to the center of the Earththe hotter it is. This explains why the rock inthe mantle is molten (melted).
The cooler (heavier)melted rock in themantle sinks as thehotter (lighter) meltedrock rises, creatingconvection currents.
Belowthemantleis thecore, thecenterof the http://www.freedigitalphotos.netearth.
Inner core, solid ironThe core is also and nickeldivided into tworegions, the innercore and the outercore. Scientistsbelieve the outercore is a liquid andthe inner core is asolid. Outer core, liquid iron
Let’s see how themake-up of thisplanetary ballaffects how somelandsforms are created.Remember that landforms arefound on a very thin crustfloating on top of a thick layer ofmolten (melted) rock calledmagma. http://scign.jpl.nasa.gov/
Next, the crust ofthe Earth isbroken into hugepieces of rockcalled plates.These plates fittogether aroundthe globe like agiant jigsawpuzzle.
The platesfloat on the hot, melted rock found in the mantle.Creative CommonsWikipedia Commons
• We learned that because of convection themagma below the magma flows, very slowly,in large patterns. Creative Commons Wikipedia Commons
Because of convection,the cooler (heavier)melted rock in themantle sinks as thehotter (lighter) meltedrock rises creatingconvection currents.These currents rubagainst the bottom ofthe plates and causethe crustal plates tomove.
Map courtesy NOAAHere are the 7 major plates plus several smaller ones.
Another day we will see how theknowledge you have gained about theinterior of the Earth and the plates thatmake up Earth’s crust helps youunderstand how some Earth’slandforms are formed.