Could life on earth owe its origins to an icy environment?
At last we have a full science-based theory on how life on Earth could have originated

In follow-up work to Miller and Urey's groundbreaking study look at the synthesis of organic compounds in a primordial environment, it was shown that RNA monomeric bases could form under conditions similar to those of a prehistoric Earth.  More recent work has shown how such individual bases, floating in a water environment, could link together into chains.

But none of that explains how the life made the jump from RNA to DNA and how it added a protective and sustaining soup of organic compounds along the way.  The answer may lie in a little known concept -- RNA can act as an enzyme.

It is now generally regarded in most of the biochemistry community as sufficiently proven that RNA acts as the enzyme to make the proteins in our body (the so called "ribozyme").  Thus it doesn't take a huge leap of logic to think that RNA enzymes, despite their lesser catalytic prowess, could slowly generate sugars, proteins, phospholipids and other key macromolecules.  In fact, a number of RNA enzymes that generate various organic molecule types have been discovered -- including enzymes to accomplish self-replication of the enzymes themselves.

A critical question that remained unanswered, though, was how the ancient RNA enzymes could survive.  RNA naturally undergoes hydrolysis reactions in water that can break its chains.  While occurring at a low rate, the large number of the phosphodiester linkages in a long RNA chain make it virtually inevitable that and RNA molecule would break apart in days, if not months.  So how did our potential RNA ancestors escape destruction?

Now researchers at the MRC Laboratory of Molecular Biology in the United Kingdom think they have cracked that puzzle.  By placing RNA inside liquid pockets of water encased inside cooling ice, they found that RNA enzymes could function and at the same time escape degradation.  At these cooler temperatures the energy barrier was presumably too high for uncatalyzed hydrolysis of the phosphodiester linkages to occur -- thus safeguarding the RNA.  But with sufficient ions (added via dissolving commonly occurring salts like magnesium-halogen salts in water), the RNA enzyme could lower the energy barrier of the desirable reactions and survive and self-replicate.

Thus the origin of life on Earth might not have been in a deep-sea vent or open ocean, but in a cold muddy puddle in the icy north or south, which contained a mix of water and organic byproducts of freed carbon from the Earth's crust.

The study's lead author Philipp Holliger explains, "It’s like the tortoise and the hare problem.  The tortoise is slower, but it keeps on going, rather than falling apart. One thing that was available at the beginning of the Earth was time."

Over time this life form could have built up an arsenal of useful chemicals -- evolution at its most basic microscopic form.  The most critical developments would have been the creation of a protective phospholipid bilayer, the creation of protein enzymes to offer faster catalysis, and last, but not least, the switch to the more chemically stable DNA.  Once a self-replicating RNA-lifeform gained these adaptations, it would at last have been ready to venture into warmer climates and begin to survive and reproduce, capturing the sun's power to fix energy in carbon-based molecules.

From there a long evolutionary road lay ahead, eventually reaching man and our zoological peers in the modern world.

So is the theory true?  We may never know.  But it appears that science has at last provided a somewhat plausible explanation as to how life could have made the leap from carbon compounds to a complex living system.

The new study is published in the September 21 edition of the journal 
Nature Communications.  It builds upon this previous 2004 study, published in Astrobiology, which suggests that RNA enzymes could have functioned in an icy environment.

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