I'm going to try to finish up the summary of our last meeting here in this post, because the excessive number of sub-parts is getting kind of ridiculous.
I still have one more point to cover here: are there chemical pathways, relevant to the conditions on the early earth, by which life's precursor molecules could have been made? If so, we should be able to deduce these pathways through conducting laboratory experiments.
So, what is the current state of biochemical pathways pertaining to the origin of life? Let's start with a history lesson. Most biology textbooks these days discuss seminal work by Stanley Miller in the 1950's (called the Miller-Urey experiment) in which he bubbled water vapor into a chamber filled with ammonia and methane (hydrogen-rich gases thought to comprise the primordial atmosphere). After simulating lightning with electric discharges for a long period of time, he found that some simple amino acids had formed in the reaction chamber! Subsequently, the origin of life research community had great optimism that the solution to the origin of life problem was just around the corner.
Fast forward 50+ years to today. Now we know the primordial atmosphere did not have the composition that Miller thought it to have. (Instead of reducing gases, such as ammonia and methane -- which have lots of hydrogen atoms -- it contained oxidizing gases, such as carbon dioxide and oxygen.) Most origin of life researchers today consider the Miller-Urey experiment to be irrelevant to the origin of life.
Most scientists today consider something called the "RNA world hypothesis" to be central to the origin of life question. Today, we live in a DNA-protein world, where DNA stores genetic information, and proteins catalyze the biochemical reactions. It would be difficult to envision that life could originate that way, since you would have to get two extremely rare events happening simultaneously: the chemical origins of DNA and of proteins. On the other hand, RNA can fulfill both roles, albeit slightly less efficiently. RNA can store information in the same way DNA can (but is less stable), and some RNA molecules can catalyze reactions similar to what proteins do (but not as well). So if the first life-form was RNA-based, instead of DNA/protein-based, then this would eliminate a major barrier to the likelihood that life arose naturalistically. Later, DNA and proteins could have slowly replaced RNA in its roles as information carrier and reaction catalyst. (This replacement would have been more or less permanent because DNA and proteins are better at their respective jobs than the RNA was.)
Now the question comes down to identifying a reasonable way in which RNA could have formed on the early earth. However, efforts to do this have been met with uninspiring results. In 2002, at an origin of life conference, here is how one leading origin of life researcher (Leslie Orgel) put it: "It would be a miracle if a strand of RNA ever appeared on the early Earth."
However, perhaps he was too quick to pronounce the miraculous-seeming nature of life's origin. Research published this year on the synthesis of nucleotides (the building blocks of RNA) demonstrated that perhaps it would be less-than-miraculous if a strand of RNA appeared on early Earth. On the other hand, some in the scientific community are skeptical. Leading origin of life researcher Robert Shapiro (and by the way, if I had to identify the three leading origin of life researchers of the 20th century, I would have said Miller, Orgel, and Shapiro) had this to say of the recent work: "The flaw with this kind of research is not in the chemistry. The flaw is in the logic -- that this experimental control by researchers in a modern laboratory could have been available on the early Earth."
In other words, even our best efforts to determine the chemical pathways to life's precursors suffer from one thing: the hallmarks of intelligent design.
Ugh. My entire summary suffered from the hallmark of intelligent design. Like I've said in previous posts, we don't want to construct an argument from a negative point of view, saying, "Look how crazy-complex this is...it must have been an intelligent designer." However, I do find these arguments regarding the origin of life to be intellectually compelling, just not scientifically defensible.
Until next time...