Microbes may be very small in size but their sheer numbers and remarkable adaptability to the existing climates is astounding. The word microbe is derived from micro-organisms meaning they are so small that they cannot be seen with naked eyes. A microscope is required to see them. But these tiny organisms are so active that they can bring about mammoth changes into the environment in which they live. Most of the chemical changes on the earth are brought about by these microorganisms.
When the earth first formed, the atmosphere consisted only of carbon dioxide and water. Due to this iron existed in the soluble ionic forms in the water. And also there was organic matter. But in the water lived the earliest bacteria called cyanobacteria which were the first photo synthesizers. They harvested the solar energy by combining carbon dioxide and water using sunlight and turned it into their food. Oxygen was the byproduct of this process. Then why did we said there was no free oxygen in the atmosphere and anaerobic conditions existed. Sure oxygen was produced but hungry sinks for it were readily available. Foremost was the iron in the soluble form. It immediately captured the produced oxygen and formed oxide an iron ore. Thus iron started rapidly getting precipitated as oxide ore. Similarly organic matter acquired its share of oxygen. Thus all the iron ore we see on the earth is the handiwork of microbes.
Slowly and slowly, all the available iron was precipitated. Now nothing was there to capture the free oxygen which these microbes were continuously producing as a byproduct of food making. Over the period of time, atmosphere was enriched with oxygen. This free oxygen was poison to many microbes which were adapted to conditions reducing conditions. So they were exterminated. But as we said in the beginning, some of them got buried deep along with organic matter and survived.
It has been reported that amongst these microbe consortia exist a class which uses carbon dioxide and hydrogen to synthesize methane gas. So far it was thought that methane was produced under aerobic conditions but evidence now credits its production to the anaerobic bacteria. These bacteria are the terminal stage actors. Before them are a variety of other bacteria which breakdown the organic matter and provide carbon dioxide and hydrogen to these bacteria.
The methane in the gas hydrates which hold the promise to solve the energy requirements of the ever hungry industrial world is formed by these microbes and has been trapped in the ice lattices in the form of clathrate compounds which are nothing but cages formed by the water molecule and methane is trapped inside. These bacteria are thought to be starved for food and are ready to pounce on the reactants as soon as they are available.
Microbes are thus omnipresent and affect the life on our planet since the life began with them.