World Builders™                                                                 Session Four  --  Microbiology             

                         The Emergence of Life     

We do not yet know how life began, but here are some theories!

Our planet project is guided by the laws of science as we know them. However, we do not know how life began.

Is life a disease of matter, something that will appear anywhere in the universe if favorable conditions exist? Is its appearance a miracle, a conscious act of Divine creation? Is it an accident? For the purposes of this course, the appearance of life on your planet does not have to be explained. Your life forms must be adapted to their environmental conditions, however, and must interact in simple ecological communities. This will be challenging enough!

Scientists have several ideas about how life may have developed here.  They include

The Warm Little Pond Theory

After Charles Darwin published his book On the Origin of Species a natural question was, What have we evolved from?  This led to questions about how life began.  One idea was that a warm, quiet lake or pond that contained a rich mixture of organic (carbon containing) molecules could have been the place where life began.  In 1953, Chemists Stanley Miller and Harold Urey at the University of Chicago performed an interesting experiment.  They put some water and simple inorganic molecules (such as ammonia, water vapor and methane) in a sealed flask and ran electrical sparks through  the mixture.  After a few days they tested the contents of the flask and found that more complex organic molecules had formed, including some amino acids, which are the building blocks of proteins.  Inspired by these results, other scientists did variants of this experiment, and were able to show that under similar  conditions a number of more complex organic molecules would form.  However, it is a long way from complex molecules to living cells, and it is now believed that the early atmosphere differed from the one provided by Miller and Urey.  This interesting idea is still being tested and discussed.

The Extremeophiles

Now, world builders, as you are resting up from visiting your hot, violent young planet, surely you remember the lava fountains, the smash of incoming asteroids, the hot, unbreatheable air, and the general inhospitality of the place.  As scientists have discovered life forms living under difficult conditions, they have come up with some new theories.  These theories have been supported by research into DNA, the molecules that are the genetic code for life forms.  By studying and comparing DNA from different life forms, the scientists are mapping out the relationships of organisms to each other.

Some scientists wonder if life could have originated in or around deep sea volcanic vents, where hotter than boiling water wells up, carrying metals, minerals, and sulfur.  Rcently discovered life forms cluster around vents in our present day oceans, and their discovery excited and amazed scientists.  These are life communities that still have autotrophs and heterotrophs, but do not use sunlight as their basic form of energy.  On a violent, hot, and unstable earth, these organisms might have been the first life forms.  They would have been protected from much of the falling space debris, and also the ultra violet radiation, if they were deep under water. 


Other scientists wonder if perhaps life came to earth from other planets, perhaps from an earlier and well watered Mars, or planets from another solar system.  Our own space journeys have shown that microbes on the outside of, for instance, a space camera, are still alive when they return to earth despite spending time in the low temperatures, dehydrating conditions, and airless environment of space.  We do not know how long microbes could survive in space.   However, a planet is a very small target out in the vastness of space, and many spores would be needed if even a few were to land on our planet by chance

A related theory asks if the organic molecules might have been assembled in the cold ices of comets.  Amino acids have been found in this ice, and also in meteorites, and some of these molecules have survived their fiery descent through our atmosphere. 

Creating Structure on Clay

Life on our planet is cellular.  This means that the organism contains itself in a little packet, a cell wall or a cell membrane, that encloses the molecules necessary for its life and reproduction.  The cell has to be able to let the useful chemicals in and keep the other materials outside itself.  However, this poses an unsolved problem:  How and why would a cell membrane evolve if there was nothing inside it?  And how could the complex reproductive molecule evolve unprotected in a boundless water environment?  These are important unanswered questions, but some scientists think that the molecules could have evolved structurally if they built themselves in clay, which has very small, thin, flakes that might have provided a structured, sheltered environment in which the complex molecules could have become assembled.

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