Originally posted by Darfius
If you're waiting for an atheist to post, you'll be waiting for awhile. They don't have any answer except "God didn't do it, that's for sure!"
And then they drool.
Anyway, God did it.
That's a rude post, Darfius. That attitude is why many others aren't respectful to you.
I'm not sure how far before the beginning of life you want me to go. I'll start here:
The Earth probably formed about 4.5 billions years ago. It was a hot, inorganic ball of rock with oceans and an atmosphere containing nitrogen, carbon and hydrogen atoms in some gaseous form or another, but no oxygen gas (O2). I don't really know what molecules these atoms were organized into, but it doesn't really matter. When gasses of made up of these elements are exposed to lightning, ultraviolet light or heat, simple organic molecules will form, as demonstrated by Stanley Miller and Harold Urey in 1953, and I believe others since.
Amino acids, short proteins, nucleotides, ATP (and probably other nucleoside triphosphates), and other molecules characteristic of living things are some of the organic molecules that have been observed to form in laboratory recreations of these conditions. In addition, we know from present day meteorites that such meteorites often cary such simple organic molecules with them. Such molecules are vulnerable to uv radiation exposure from the sun (no ozone layer yet) but some places, like tidal pools hidden under rocky shelfs, would be shielded from uv exposure.
Some such pools would have had ocean water splashing into them during high tide, bringing with it the organic molecules in it, and during low tide some of the water in the pool might have evaporated. By this or some other mechanism pools of water sheltered from uv radiation would become highly enriched in the organic molecules. As there was not yet any life and no free oxygen, these molecules had no environmental influences that would break them down.
When organic molecules like these are placed in concentrated enough solutions, they spontaneously react to form more complex organic molecules, such as RNA.
RNA molecules with all kinds of random sequences would spontaneously form. Now we know that RNA, like proteins, folds into specific configurations depending on the sequence of bases it is made up of. Sometimes the folded RNA is catalytic; that is, it makes an enzyme. Such RNA enzymes are called ribozymes.
Now RNA, like DNA, already has an obvious mechanism by which it could replicate itself. This is the point at which substances began to catalyze the synthesis of smaller molecules into copies of themselves; that is, they reproduced. Being genetic material with no proofreading systems with the potential to be exposed to uv light, such RNA chains began to mutate into chains with slightly different base sequences. Any of these which folded into enzymes that catalyzed their own reproduction would begin to out compete the other RNA chains in terms of reproduction and using up the raw materials for reproduction. The process of evolution has begun, even before life existed.
Now, it's been shown that amphipathic molecules like phospholipids will tend to aggregate and form one of three different formations depending on the conditions; micelles, solid molecular sized balls of phospholipid molecules, a bilayer, or flat sheet (which would need to be anchored on the edges away from water), or a combination of the two, a vesicle. A vesicle is lipid bilayer bent into a spherical shape and closed upon itself. Such vesicles trap water and the contents of water in their cavities when they form. Small molecules can pass through the phospholipid bilayers of such vesicles far more easily than larger molecules.
Some of these vesicles probably formed around RNA which was already evolved into a form that catalyzed it's own reproduction quite effectively. Such RNA still had access to the small molecules it needed as raw material for self reproduction, but large molecules that might damage it or otherwise interfere were kept out. The RNA would reproduce and reproduce, and the new ribozymes wouldn't be able to get out of the vesicle. Maybe more than one kind of self replicating RNA would get trapped inside the vesicle and begin to reproduce.
This stage of prebiotic evolution is known as the
protocell. Such protocells could collect more and more phospholipid molecules and keep reproducing the RNA inside, causing the protocell to grow.
At this point, a number of the characteristics of life have come into being. The protocell has begun to aquire and use materials and energy from it's environment and to convert them into different forms. It was growing. It had the capacity to evolve. And, once these things grew big enough, and possibly with the help of the ribozymes inside, they would divide. This is reproduction of the entire protocell.
Now, sometimes more than one molecule of RNA would get trapped inside and begin to self-replicate; sometimes some copies of the RNA inside the protocell would mutate into different forms. In this way different enzymes would come into being, providing a more varied environment inside the protocell. Sometimes these various chains of RNA would begin to specialize into symbiotic relationships, helping one another reproduce and do other things.
As you can see, it makes perfect sense based on much experiment that such a pattern of change from inorganic, simple molecules to complexity in the form of protocells could plausibly come into being. Any entropy lessened in the formation and reproduction of these ordered objects would be compensated for by breakup of nucleoside triphosphates. This effectively changes sunlight or other ordered forms of energy to heat, which I think counts as increased entropy. So, unlike what some creationists suggest, the Second Law of Thermodynamics is not broken by this proposed mechanism.
Some of these ribozymes would begin to assemble amino acids into short chains through catalysis of dehydration reactions. Once proteins were being formed, similar evolution would produce protein catalysts or enzymes. At some point some RNA would catalyze the formation of the more stable DNA molecules, which would take over as the genetic material of these protocells.
At this point we pretty much have a primitive cell, or something close to it. Life is a poorly defined word, so there isn't any exact moment at which one could say it has been crossed. It's more of a long process full of small changes that caused the protocell - not alive - to the cell - alive. The cell then began to evolve, but that's beyond the scope of the question asked here.
This of course is not definitely known. It's simply the hypothesis that makes the most sense based on the evidence, and is generally accepted as the most likely situation by biologists. I and the scientific community are always exploring the possibilities and plausibilities of the possibilities. We're checking each other's work and competing to discover the most accurate models. As the economy of the U.S. and the First World in general shows, competition works wonders.
The other option is that I could say God did it, and we can't understand him. I could say I believe this because I had a powerful emotional experience. That sort of explanation has never really worked for anything else once it had to compete with scientific rigor, though. It also kind of ignores the fact that people often use the same process to come up with entirely different ideas about things, like Islam vs Christianity.
I prefer the first explanation. It explains more and doesn't invoke fairies or spirits or magical beings with superpowers who don't have to follow the laws of physics which everything else does. It also makes much more definite predictions which are testable, and in the past has survived such testing.
Creationism is kind of like explaining how stars work by saying there are invisible, undetectable pink leprechauns inside them making all the heat and light with pixie dust.
The begining of life
27 Feb '05 08:07
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