Earth is the only planet which we know where water is present is present in all the three forms. Seventy percent of the Earth is filled with water but only 2.5% is freshwater. Rest of it is saline water in oceans. Now, out of this 2.5% freshwater, only 1% is in usable form. This is because rest of the freshwater is locked up in ice caps and glaciers and cannot be used.
Decomposing - When plants and animals die, they decompose. This process uses up oxygen and releases carbon dioxide. Rusting - This is also called oxidation. When things rust they use up oxygen.
