Re: Why do the Continents only cover ¼ of the world's surface?

ID: 888389520.Es 

Why do the Continents only cover ¼ of the world's surface? 

Charles:

I think you've got some serious misconceptions going here.  The majority of 
the mass of the continents was constructed VERY SLOWLY over the first 
couple billion years of earth history and we are still adding very small 
amounts today.  

The idea that somehow there is "missing" continental mass and that it is 
the source of the moon is kind of far-fetched.  I suggest that you read 
about the formation of the continents in a college-level Historical or 
Physical Geology book.  

It will tell you that the continents were (are) produced (according to 
current theory) by subduction and, to a lesser degree, obduction of 
lithospheric plates and sediment eroded from volcanic islands.  Through a 
process known as partial melting, the less dense fraction of these 
materials was melting preferrentially, producing the felsic-intermediate 
(silica rich, Fe and Mg poor) composition of the continental crust from the 
mafic-ultramafic (Fe and Mg rich, silica poor) composition of the 
lithospheric plates.  Once produced, continental rocks were too light to be 
subducted and are therefore very old.   Instead, the continents just grew 
and grew, because the continual process of plate subduction provides new 
source material.  The denser ocean crust, on the other hand, is relatively 
young (< 200 million years) because it is constantly being recycled.

Dr. Clay Harris
Dept. of Geography/Geology
Middle TN State University
cdharris@frank.mtsu.edu