Expert: Ralph Salier - 10/30/2009

Question
Ralph,

What is the proper name for the 4 major land masses on earth?

I know that there are 7 continents, however, seen from space, there are only 4 large land masses (The Americas composing one, Africa, Asia and Europe composing the second and Australia and Antarctica being the others - naturally disregarding canals as man-made breaks).

Is there a proper name for these landmasses as a group? Is there a proper name for Africa, Europe and Asia as a single landmass?

I have asked these questions of various people and never received a proper answer. The Internet has so far proven to be fruitless on this subject.

I am, therefore,

Yours, in hope,

Iain

Answer
Hi Iain,

As you noted, the seven continents don't look like 7 but in reality they are.  Euroasia looks like one massive land mass but that is because the European continental plate has crashed into and has stuck to the Asian plate.  The joint between the two are the Ural mountains east of Moscow.  

The North and South American plates are actually two separate plates but are currently connected by the isthmus of Panama but from Northern Columbia through Panama and into southern Mexico, there are a string of volcanoes which created  this land.  It is on the edge of the Caribbean plate pushing into the Eastern Pacific Plate.  Africa is only connected to the Asian land mass at the Sinai Peninsula.  This, lies directly on the great Rift Valley which is the plate boundary on East side of Africa.  But Africa is on its own crustal plate as are Australia and Antarctica.  

As you may have noted by now, I am speaking of "plates".  The Earth is made up of several layers.  The outer most is the crust.  The crust rides on the molten mantle which is the next layer in and  this floats on the outer core which moves over the very hot but solid core.  The mantle moves with convection currents and these convection currents move the crustal plates on the surface.  There are both major plates and many minor plates that have been partly or nearly fully destroyed by this movement.  The continental plates are rather large and because of the nature of  the rock on them they are "lighter in weight" then those of the newer oceanic plates.  The oceanic plates are constantly expanding at the mid-oceanic ridges and  this pushes the continental plates around.  Currently the Atlantic Plates are moving east and west from the mid-Atlantic ridge and this is making the Atlantic ocean bigger while pushing North and South America into the Eastern Pacific Plate.  This is why there are so many volcanoes around the pacific ocean.  Now of course, the eastward push of the atlantic plate is pushing Europe into Asia which is pushing into the western Pacific Plate and pushing up volcanoes around the western Pacific  (The Pacific Rim of fire).  There are many smaller plates both crustal and oceanic.  

Here are some websites that show these plates and their interaction:

en.wikipedia.org/wiki/Plate_tectonics

www.ucmp.berkeley.edu/geology/tectonics.html

www.seismo.unr.edu/ftp/pub/louie/class/.../plate-tectonics.html
kids.earth.nasa.gov/archive/pangaea/
www.extremescience.com/PlateTectonicsmap.htm

I hope you find these of interest.  The subject as you can see is plate tectonics.