I am impressed that this thread has gone so far; it's good for people to actually think about these issues rather than accept the standard belief without thinking about it.

First of all, there are a huge number of reasons why life could not have originated on earth by natural occurrences.

1.) The Urey-Miller experiment: This experiment was very strong evidence against evolution 50 years ago, but is still being quoted in text books today as the origin of life.
The aim of the experiment was to be able to create extremely simple amino acids from a mixture of gases and an electrical spark, supposedly similar to the atmosphere of a "Primitive earth". The only problem is that to create these simple acids, hydrogen must be present in the mixture. Is there any hydrogen in earth's lower atmosphere, where there happens to be lightning? I don't think so. Being the lightest existing element, it will be sitting on top of all those other gases, on the edge of space.

2.)Lets just pretend that there is hydrogen in earth's lower atmosphere and an amino acid happens to form. What then? There are 22 amino acids used to make proteins in a living cell, and this experiment managed to produce two or three. A protein, by the way, is nothing compared to a cell. It is a building block of cell components, and many, many cell components must make up a single cell. DNA is totally out of the question: You need this monster to even make proteins, and it is composed of tens to hundreds of millions of nucleotides, all in the glitch free "programming" to construct the basic components of a cell. No matter how hard for how long you try, you will never arrive at DNA by chance with a couple of amino acids.

3.) The flagellum on a bacterium is composed of 50 parts that work together like an electric motor: if just one of them is out of place, the bacteria will not have propulsion. This in itself is massive proof against evolution: if this device was built up by natural selection, how was a non-functioning appendage on the back of the bacterium favoured by natural selection over the “millions of years” that it took to perfect it? Wouldn’t these bacteria have the disadvantage of extra drag and weight that would impair the cell, and cause it to die? Also, the flagellum’s “motor” is made up of parts that are all different. The cell wasn’t manufacturing these parts by chance, they were clearly part of a greater intelligence.

4.) The bombardier beetle: This is probably an overused example, but it is an essential fact: The bombardier beetle could not have evolved it’s combination of reactive chemicals without destroying itself; not only are there two separated reactive chemicals within it’s body, but it also has suppressant chemicals to stop these reactants from blowing it up. How all these could have possibly evolved at any early advantage to the organism is anybody’s guess.

I can quote more to you if you want them, but right now I have just finished my final exams and don’t have much motivation to do more essay writing. And by the way, if the 6000 years belief is mere sentimentalism, what does that make evolution? An attempt to escape from God, at the expense of rational thinking.

Now you can all tell me why I'm wrong