Diatoms are microscopic plants (phytoplankton) found in oceans and lakes. Their cell wall is made of http://wiki.answers.com/wiki/Silica which remain after the diatom dies. The skeletons of these...
One view
The Earth can be classified as a habitable planet (and it is the only one we presently know of).
Another view
A rocky planet characterised by the presence of liquid water and a chemically...