Sorry about taking so long. There’s a lot of stuff, and it’s not my specialty.
"In the natural sciences, abiogenesis, or origin of life, is the study of how life on Earth could have arisen from inanimate matter. It should not be confused with evolution, which is the study of how living things change over time." - Wikipedia
Let’s go from there. So abiogenesis isn’t evolution. It’s not spontaneous generation, either. Spontaneous generation was the idea that complex animals could appear from decaying organic matter, something obviously quite different from the orgin of life.
So what was the first scientific evidence? A. I. Oparin, noting the abundance of organic matter on other planets, hypothesized a reducing atmosphere for the earth, in which prebiotic reactions could occur. (This hypothesis was later confirmed by the presence of reduced iron compounds, which could only have formed in a reducing atmosphere) Oparin also discovered coacervates, which are vesicles spontaneously formed by some organic molecules. They feature a membrane, internal chemical concentrations that are maintained by differential movement through the surface, but do not reproduce.
Later, it was discovered that basic cell membranes are very simple bilayers of phospholipids that also spontaneously form vesicles.
http://www.sp.uconn.edu/~terry/images/cell/bilayer.gif
Over time, additional components have become associated with the bilayer, but it was a bit of a shock to see that the basic cell boundary was so very simple. A better boundary could probably be designed, but since the membrane was an absolute first step in the evolution of cellular life, it’s not surprising that it’s simpler than most everything else.
Miller-Urey, using chemicals and conditions that existed in pre-biotic Earth, showed that amino acids can form abiotically. The discovery of the Murchison Meteorite, containing abiotic amino acids (including some that don’t exist on Earth) confirmed the experiment. The fact that some of the amino acids in the meteorite had an excess of L-forms was also significant; life on Earth uses only L-forms.
Later, it was discovered that amio acids polymerize into peptides (short proteins) in nature:
Prebiotic peptide-formation in the solid state
springerlink.com/content/n07l611g6g2730r2/
Self-replicating chemical systems have been prepared and studied since the late 1980s.
molecularassembler.com/KSRM/4.1.6.htm
The big hold-up was figuring out how a replicator molecule could self-catalyze. That seemed an insuperable problem. Then this:
Self-catalyzing RNA
thelivingcosmos.com/TheOriginofLifeOnEarth/PreRnaWorld_12May06.html
But how did RNA appear?
**A significant sticking point is how RNA, self-catalyzing or not, arose in the first place. Until recently, two of RNA’s building blocks, cytosine and uracil, had proven difficult to synthesize under the sort of conditions that might have prevailed on Earth about 4 billion years ago. However, in June1995, Stanley Miller and Michael P. Robertson, at the University of California, San Diego, reported1 that they had been able to synthesize cytosine and uracil under plausible prebiotic conditions. The technique involved placing urea and cyanoacetaldehyde in an environment equivalent to that of a warm tidal pool. As evaporation concentrated the mixture, the chemicals reacted to yield cytosine and uracil in large amounts.
Further support for the RNA world view came in 1998 from researchers at Massey University in New Zealand.2 They developed a picture of a hypothetical RNA-based organism, which they named Riborgis eigensis after the German biologist Manfred Eigen. In their view, R. eigensis would have had its genes strung out along a set of linear chromosomes so that it had more in common with the genetic organization of eukaryotes than it did with the single, circular chromosome found in the cells of prokaryotes. **
daviddarling.info/encyclopedia/R/RNA_world.html
More to come.
