I don't think I agree with the conventional wisdom that it's an incredibly remote possibility that life could appear spontaneously, and that only the most perfect conditions could give rise to it. Nor do I think the Second Law of Thermodynamics is necessarily the sworn enemy of life or complex systems.
Essentially what I think is that given generally positive conditions, complex molecules and life are almost inevitable. My reasoning is that the building blocks of all material are the simplest forms of matter. These simple elements are acted upon by heat, electricity, light, radiation, and pressure and combine into heavier gases, minerals, and metals. These further react with other elements to form alloys, compounds, and molecules. Altogether relatively simple reactions, with the result over billions of years being a veritable petrie dish of varied, albeit simple chemicals. Some of these are highly reactive, others inert, others catalyzing reactions between other chemicals. You see varying concentrations of certain chemicals in eddies, pools, oceans, planets or even solar systems. While the original building blocks are relatively simple and homogeneous, slight variations during galactic or planetary development give rise to countless variations and concentrations of these chemicals. An infinite number of reactions occur with an infinite number of results. From any one reaction you will see one or more chemicals reacting with one or more other chemicals to produce byproducts. Energy or other chemicals. One isolated reaction has little effect on the system, but billions of reactions can have significant impact on the environment. Perhaps hydrogen and oxygen are reacting to form water. If this water molecule is stable and no reactions occur that further modify it, then the molecule will stick around. Over time, more and more water will form and less and less hydrogen and oxygen will exist (provided they are not being actively generated by other forces). In this scenario the environment is more suitable to the more complex chemical: water, than to the two simpler elements: hydrogen and oxygen.
It's very difficult to describe this theory without using language that ascribes some sort of human trait to these chemicals. "Water, oxygen, and hydrogen are in competition with each other and water wins because it is best able to survive and reproduce." However the fact of the matter is that it's simple statistics. There are still far more simple chemicals than complex ones, yet some complex chemicals will form that have a more stable structure that prevents them from breaking down instantly.
The diversity of the system as a whole further increases. More reactions take place. Some chemicals catalyze other reactions, allowing a small quantity of one chemical to cause large quantities of other chemicals to react, producing large quantities of product. Self-catalyzing reactions are self-sustaining provided there are sufficient reactants to feed the reaction. More molecules are generated and, statistically, some of these participate in fewer subsequent reactions and tend to increase in quantity. Others are obliterated almost as soon as they are generated, causing even more reactions.
In fact, to cite the previous, hypothetical example, if hydrogen and oxygen combine to produce water, then you have an even greater opportunity for reactions to take place. Water is an extremely effective solvent, so any large quantity of water will tend to have massive quantities of other elements dissolved in it. This chemical tonic brings more and more chemicals together, encouraging reactions. Currents and convection keep the mixture in flux, generating even more reactions. In fact, this type of action can form complex systems that are self-sustaining. Chemical A reacts with Chemical B at the bottom of a body of water. This generates Chemical C and heat, causing the water to rise. This rising water is bombarded by ultraviolet light as it approaches the surface, generating Chemical A, which subsequently sinks and begins the cycle again. It's this kind of complex system that really kicks things into high gear. Certain chemicals begin to concentrate in certain parts of the system and these high and low concentrations -- and their interactions with each other -- cause even more varied and complex reactions. What we're seeing is that over time, trends will form and statistics dictate that some complex systems will develop and stabilize.
What happens if certain molecules combine or bind? What if a catalyst binds to a product of a reaction? Then that product will carry with it the key to generating even more molecules like it. What if a molecule binds with another molecule that makes the two more stable? What if Molecule A is highly sensitive to ultraviolet light and quickly breaks down in its presence. However Molecule A binds with several molecules of Molecule B which block this ultraviolet radiation and allow Molecule A to remain a part of the system?
We're still talking completely inanimate chemical reactions yet we can see already flashes of how life works. Chemicals thriving under ideal conditions. Ecosystems, cell walls, reproduction. When you bite these things off in little chunks they aren't so hard to digest. As chemicals form into more and more complex systems you see molecules teaming up with other molecules into structures that are more stable and offer more protection. Products bind with catalysts resulting in more reactions. Products combine with catalysts and other molecules which surround and protect them. Over millions of years you find advanced carbon-based molecules surrounded by proteins which protect it. The right combination of chemicals causes this molecule to react with those chemicals in the presence of catalysts, to form an exact replica of itself. This molecule then reacts with other protein molecules which bind to its outside, which creates an exact replica. Cell wall and the precursor to DNA. All after trillions of previous reactions, trillions of failures, and eventually through the magic of statistics, success. Statistics is, after all, the science of magic. Because no matter how improbable an event might be, no matter how many times it fails to happen -- if it's physically possible -- it eventually will happen.
And this improbable new structure, even though it's a single one in a sea of others, has a decent chance of survival because it was built with stable molecules. Molecules that had stood the test of time. And it was surrounded by proteins; proteins that through time had made this molecule more stable and less likely to be broken down by heat or UV radiation. And in the right conditions it could make a duplicate of itself. An exact replica. And this exact replica would, in turn, be able to react with proteins to form a protective coat that would shield it until, it too, could make an exact replica of itself. My theory is that the magic of statistics means that complex systems are virtually inevitable given enough time. Ideal conditions help, but the beauty of statistics is that eventually the right conditions will arise. And then the inevitable will happen. A million compatible systems may be destroyed by a passing comet, or a supernova, or simply a system that reacted itself into stagnance. But statistics dictate that the improbable must happen, given enough time.
And yet cutting through this theory at all levels don't we have the second law of thermodynamics? The great debaser? The guarantor that complex systems cannot arise without external forces? No. The second law neither precludes this, nor is at all at odds with this. In fact, it's the force which prevents this process from spiralling out of control and eventually crashing in on itself.
This theory is based on the concept of hierarchy. That cosmic quantities of light elements form incredible quantities of heavy elements which become enormous quantities of molecules which, in huge numbers of complex systems form giant numbers of molecular systems which combine into many, many living cells which make lots of organisms which eventually leads to quite a few complex organisms culminating in a small quantity of pink creatures called "Homo Sapiens". And if this hierarchical structure sounds familiar, it is. It's the evolutionary chain. But it's also the food chain and I think they're one of the same. And both can be traced all the way back to nebulous clouds of hydrogen.
Cosmic quantities of simplicity interact to form limited quantities of complexity. Yet the system as a whole remains stable. It is the hierarchical nature that is why the second law does not preclude this from ever happening. Statistics make it an inevitability that complexity will arise, while the second law makes it an inevitability that the reaction is self-limiting and cannot spiral out of control until every atom in the universe has evolved into a man. Even though the result is guaranteed, such a small part of the overall system ever reaches this level of complexity that the second law is never violated.