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Response to caraher (Reply #1)

Mon Feb 4, 2013, 04:36 PM

13. Chemical evolution

Here's a definition of chemical evolution from: http://dictionary.reference.com/browse/chemical+evolution

The formation of complex organic molecules from simpler inorganic molecules through chemical reactions in the oceans during the early history of the Earth; the first step in the development of life on this planet. The period of chemical evolution lasted less than a billion years.

Note : Many of the steps in chemical evolution can now be reproduced in the laboratory.

Note : Some scientists believe that all or most of the Earth's original organic molecules were created in space and were brought to the Earth's oceans by meteorites.

So, you see, there are some interesting scientific questions to be discussed and decided about chemical evolution.

Richard Dawkins has a 20 or so page discussion of ideas associated with the chemical origins of life in his wonderful book The Ancestor's Tale, at the point when all the ancestors have returned to 'Canterbury' about 4 billion years in the past:

The origin of life was the origin of true heredity; we might even say the origin of the first gene. By first gene, I hasten to insist, I don't mean first DNA molecule. Nobody knows whether the first gene was made of DNA, and I bet it wasn't. By first gene I mean first replicator. A replicator is an entity, for example a molecule, that forms lineages of copies of itself. There will always be errors in copying, so the population will acquire variety. The key to true heredity is that each replicator resembles the one from which it was copied more than it resembles a random member of the population. The origin of the first such replicator was not a probable event, but it only had to happen once. Thereafter, its consequences were automatically self-sustaining and they eventually gave rise, by Darwinian evolution, to all of life.

A length of DNA or, under certain conditions, the related molecule RNA is a true replicator. So is a computer virus. So is a chain letter. But all these replicators need a complicated apparatus to assist them. DNA needs a cell richly equipped with pre-existing biochemical machinery highly adapted to read and copy the DNA code. A computer virus needs a computer with some sort of data link to other computers, all designed by human engineers to obey coded instructions. A chain letter needs a good supply of idiots, with evolved brains educated at least enough to read. What is unique about the first replicator, the one that sparked life, is that it had no ready supply of anything evolved, designed or educated. The first replicator worked de novo, ab initio, without precedent, and without help other than from the ordinary laws of chemistry.

Dawkins presents some of the research done in investigations of chemical evolution, for example, the Miller-Urey experiment:

What Miller, under Urey's direction, did was take two flasks, one above the other, connected by two tubes. The lower flask contained heated water to represent the primaeval ocean. The upper flask housed the mocked-up primordial atmosphere (methane, ammonia, water vapour and hydrogen). Through one of the two tubes, vapour rose from above the heated 'ocean' in the lower flask and was fed into the top of the 'atmosphere' in the upper flask. The other tube returned downwards from 'atmosphere' to 'ocean'. On the way it passed through a spark chamber ('lightning') and a cooling chamber, where vapour condensed to form 'rain' which replenished the 'ocean'.

After only a week in this recycling simulacrum, the ocean had turned yellowbrown and Miller analyzed its content. As Haldane would have predicted, it had become a soup of organic compounds, including no fewer than seven amino
acids, the essential building blocks of proteins. Among the seven were three glycine, aspartic acid and alanine from the list of 20 found in living things. Later experiments along Miller's lines, but substituting carbon dioxide or
carbon monoxide for methane, have achieved similar results. We can draw the robust conclusion that biologically important small molecules, including amino acids, sugars and, significantly, the building blocks of DNA and RNA, spontaneously form when various versions of the Oparin /Haldane primitive Earth are simulated in the laboratory.

These snippets don't do justice to the whole discussion, but at least should give you some ideas about scope of work on life's chemical origins.

I hope Colorado high school students get to learn about THIS SORT OF INTERESTING, AMAZING WORK!

Fun stuff.

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caraher Feb 2013 #1
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