Noun: technical term for spontaneous generation.So, basically, 'abiogenesis' refers to the spontaneous generation of life from non life. I have previously blogged on the definition (or lack thereof) of 'life' in What Is Life? which, interestingly and maybe significantly, no creationist has yet been able to answer, nor to refute my biological definition of life as localised entropy reduction.
Origin: late 19th century: from a 'not' + Greek bios 'life' + genesis
What creationists insist on trying to insert into the definition is some form or magic ingredient called 'life' which is always left intentionally vague and ill-defined. Of course, from a biologists perspective, all that is necessary is to define 'abiogenesis' as the origin of replicators since the process of evolution can take it from there. 'Life', for a biologist, is merely shorthand for metabolism, which is necessary in complex systems for reducing the local entropy by increasing it elsewhere.
Before listing a few of the very many different theories and hypotheses concerning how a first replicator could have arisen on earth, let me pause to dispel one cherished myth Creationist pseudo-scientists like to promulgate to their target market: that the theory of evolution includes abiogenesis and that somehow, failure to 'prove' how abiogensis magicked up the magic ingredient called 'life' destroys evolution as a credible scientific theory.
This is the equivalent of arguing that failure to explain the origin of the stone which will fall to earth when dropped, destroys gravity as a credible scientific theory or that failure to explain why electrons form shells around an atomic nucleus renders Avogadro's Law false.
The Theory of Evolution is a scientific explanation of the fact of evolution, just as Newtonian and Einsteinian gravity are scientific theories to explain the fact of the force of gravity. The theory of evolution deals with how replicators evolve and diversify over time, not how they originated. We know they originated because we can see them, so the question of how they originated is of mere academic interest to biology. It's the equivalent of a hydrologist being asked to prove that the water in a river started from high up in the sky, and telling him that wet ground following rain doesn't prove anything, or the river doesn't exist.
Indeed, the explanation for abiogenesis is by definition to be found outside of biology altogether and in the realms of chemistry and physics. Quite simply, it is not a major concern for biologists.
And remember, the fact of evolution means that abiogenesis only needed to happen once! That's not to say it did only happened once, just that it only needed to happen once. The other thing to remember is that we know there were living things by at least 3.5 billion years ago, so it must have happened in the first billion years of earth's 4.5 billion year life. (For American Creationists, that's a really big number of years: nearly 4 million times as long as there has been a USA! If you stretch your arms out with your fingers extended, with the tip of your left middle finger being the start of the earth and the tip of your right middle finger being today, 1 billion years is about up to your left elbow. The whole of recorded human history is in a single stroke of a nail-file on your right middle finger. You see now why Creationist pseudo-scientists want you to think earth is only 6000 years old?).
Okay. Let's look at a brief selection of the different theories and hypotheses concerning abiogenesis - i.e. the origin of physical replicators. I don't propose to list them all here. After all, if you aren't going to read about them on the Wikipedia article, you probably won't read them here either.
Remember, science is not obliged to explain a magic ingredient called 'life' unless you can show there is such a thing. That's just another of the evidence-free myths you need to believe if you are religious.
These are all taken from Wikipedia where they and more can be read in much greater detail.
- Primordial Soup. In the oxygen-free atmosphere of early earth, organic molecules could be formed by electrical discharge (lightening) acting on water, ammonia, and methane to form more complex organic molecules such as amino acids and sugars. In a famous experiment, Miller and Urey showed that this is possible. A subsequent analysis of sealed samples of their original extract using more sensitive analytical techniques than in the 1950s shows that there were actually 23 different amino acids present, not the 5 originally reported. In this soup, free from oxygen and living systems which would have destroyed or consumed these molecules, they were free to build more complex systems at random following basic laws of chemical reactions.
- Proteinoid Microsperes. Sydney W.Fox has shown that, in conditions which may have existed on pre-biotic earth, amino acids can spontaneously form peptides (short chains of amino acids) which will them form proteinoid microspheres with some of the basic characteristics of living things.
- Deep Sea Vents. Hydothermal vents created a chemical gradient, in which conditions are ideal for an abiogenesis and where an electron donor such as nacent hydrogen can interact with an electron receptor such as carbon dioxide.
- Self-replicating Hypercycles. Manfred Eigen and Peter Schuster of the Max Planck Institute for Biophysical Chemistry showed mathematically that an information storing system such as RNA can code for the formation of an enzyme catalyst which can create another information system in sequence until the original information system is coded for again. These hypercycles can create quasispecies out of chemical chaos, which would be subject to Darwinian selection and evolution. However, this hypothesis relies on the presence of nucleotide which have not been shown to form in the Miller-Urey experiment.
The RNA world hypothesis proposes that self-replicating ribonucleic acid (RNA) molecules were precursors to current life based on deoxyribonucleic acid (DNA), RNA and proteins. RNA is able both to store genetic information, like DNA, and to catalyze chemical reactions, like an enzyme protein. It may therefore have played a major step in the evolution of cellular life [...] DNA is thought to have taken over the role of data storage due to its increased stability, while proteins, through a greater variety of monomers (amino acids), replaced RNA's role in specialized biocatalysis. The RNA world hypothesis suggests that RNA in modern cells is an evolutionary remnant of the RNA world that preceded ours. Also, many critical cofactors (ATP, Acetyl-CoA, NADH, etc.) are either nucleotides or substances clearly related to them.See also RNA World hypothesis.
- "Primitive" extraterrestrial life. Although 'life' could of course have originated on other celestial bodies and been transported to earth on meteroites, these are not really explanations of abiogenesis, which would still remain to be explained, though they could explain how these early replicators came to be on earth.
- Multiple genesis. Just because it looks like all living things originated from a single common ancestor, does not mean that common ancestor did. Just as we now suspect that complex (eukaryote) cells originated as symbiotic associations of simple (prokaryote) cells, so the early prokaryote cells could have arisen as symbiotic associations of simple replicators. This would imply that the various different theories need not be mutually exclusive. For example, autocatalysing RNA could have found itself in liposome or become wrapped in a peptide chain which formed part of a hypercycle.
Of course, all science needs to do is propose plausible hypotheses which build on the known. Whether any of them are a true and accurate description of exactly how abiogenesis happened is largely irrelevant and can wait to be established. We know it happened because we can see the result.
You, however, have to prove your god, and only your god, exists before you can plausibly hypothesise it as a cause. Why can you never do that?
Until you can, your inclusion of magic, miracles, and a magician whose origins are a mystery and for which you need to invoke infinity, will always produce an infinitely more complex, infinite less vicarious and therefore infinitely implausible explanation than anything science can produce. That's the great thing about basing your theories on reality.