Re: Are there more organisms in the ocean or on land

You want to know about populations of organisms of one cell or more.  That 
includes every known life form.  Your question hints at something, and you 
are correct about what you hint, unicellular organisms, organisms composed 
of a single cell, out number multicellular organisms by such a huge 
proportion that in terms of numbers it's essentially correct to say that 
life on Earth is predominately unicellular.  

You ask if there are more numbers of organisms on land or in the oceans.  
First there is a big difference in the amount of land and water covering 
the surface of the Earth.  The oceans cover nearly 2/3s of the planets 
surface, so oceans are twice the area of the land.  Even though most of 
the open oceans are nutrient poor and life is spread very thinly, the 
populations of planktonic organisms living in the oceans are huge.  There 
are countless unicellular organisms in virtually every gallon of sea water.

Of course lots of organisms live on land too, but don't bother counting 
insects and other animals, or plants, there aren't enough of those to 
matter much in the comparison.  Every cubic inch of soil, a volume about 
the size of a sugar cube, is estimated to contain between 9 and 21 million 
organisms.  Enough soil to fill a four inch diameter flower pot, about big 
enough for one small plant, would harbor 12 billion organisms.  

Based on size and volume, I would guess there are more organisms in the 
oceans, but scientists have made some recent discoveries that reveal even 
more organisms in an even more unlikely location.  Deep within the Earth's 
crustal sediments, in the rocks beneath the land and oceans live countless 
microorganisms, mostly a group of prokaryotes called Archaebacteria.  Such 
organisms live in deep, hot places, and scientists were actually surprised 
to find them, and in such numbers.  Many of the Archaebacteria are 
extremophiles, literally lovers of extreme environments, and others are 
found in very hot, acidic springs or very salty water at the Earth's 
surface.  In the geothermally heated oil fields of the North Sea, the 
production fluids from 3500 meters deep contain any where from 100,000 to 
100 million organisms per milliliter, a cubic centimeter of fluid!  
Boiling sulfurous mud baths in Iceland contain up to 1 billion organisms 
per milliliter.

So where are the most organisms?  Probably not either on land or in the 
oceans, but the largest population of organisms lives in the crustal 
sediments deep beneath our feet, a region that covers the whole Earth.  
And until very recently this abundant life was virtually unknown.  This is 
so new to science that it isn't in the textbooks yet.  And that's why some 
scientists take time to answer questions, so we can tell you about things 
that are new to science.