Ask A Scientist General Science Archive

Author:     library
Text:       1) What percentage of the earth is water today?  2) Has this 
percentage changed?  3) How many people are there on Earth?  4) How much of 
the earth is salt water and how much is fresh?

Response #:  1 of 1
Author:      woodford
Text:        Nearly 78% of the earth's surface is covered with water today.  
The majority of that 78% is oceans.  This number has fluctuated over 
geological time with the growth and melting of the polar ice sheets during and 
after the ice ages.  At times the oceans were about 400 feet lower than today, 
exposing much more land surface.  This happened when large quantities of water 
were locked up in glaciers.  Today we are seeing a slow (millimeters per year) 
rise in the ocean levels.  Whether this is cyclic or due to global warming, is
in dispute.  The answer to your question 3 is that the population of the earth 
is now around 5 billion people.  The answer to question 4 is 97.3% of all of 
the water on earth is saltwater.  The remaining is freshwater of which 2.1% is 
in glaciers and polar ice, 0.6% is underground water, 0.01% is in lakes and 
rivers, and 0.001% is in the atmosphere.  All of these percentages are very 
near approximations.  Hope this helps. Thanks for writing.