Steve
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Life in the Air

It has been recognised for many years that there are bacteria as well as other things like viruses and algal and fungal spores in the air.  In the time of Louis Pasteur great efforts had to be made to prevent the contamination of cultures by bacteria in the air of the laboratories.  It is still very important today.

Not a Habitat?

When I was at school, we were taught that although there are plenty of bacteria in the air, it is not a place where they can grow and live.  More recent research shows that this is incorrect.  Clouds have all the things necessary for some bacteria to live, grow and reproduce.  In fact they can do these things quite quickly.

How High

It used to be believed that no bacteria or other living things could go very high into the atmosphere.  Although measurements do show that the concentration of bacteria decreases rapidly with altitude, even at 70 kilometres up, some samples show significant numbers.  This leads to the question; what is the absolute upper limit for bacteria? And even; is there an upper limit? 

Experiments have shown that some bacteria as well as the resistant spores of several groups of living things can survive in space.  Could bacterial spores even leave our planet and make their slow way to other planets?

The Origin of life

We tend to think that the life forms of the Earth were either created, evolved, or both, entirely on our Earth.  If we accept the possibility of our life forms going to other places in our Solar System, then it is also possible that life has come here from other places. 

My own feeling is that our life forms did originate on the Earth, but I cannot offer any clear proof that this is so.  Could the first life forms in the Solar system have originated on Mars which cooled faster than the Earth, and have come here, possibly on meteorites from Mars a few billion years ago?