Science is supposed to be about things that are observable. That is, science can probe only things that we can detect with our five senses. Science also must be repeatable. This means that when an experiment or observation is repeated, we get the same results. These restrictions on science have led to what we call the scientific method, the general rules that we follow in doing science. The scientific investigation of the origin of life presents us with at least two problems. First, since life began before people were around, we hardly can observe the process. Second, since the origin of life appears to have been a unique event, we hardly can repeat it.
How do these four possibilities stack up? The fourth possibility doesn't really explain how life came about, but instead passes the question off to some other location. Many would object that the third option is unscientific and hence ought not to be considered. If we restrict the definition of "scientific" to questions that can be answered through the application of the scientific method to natural processes, then option three may be considered unscientific. However, what is the status of the other two options? Option one is the assertion of abiogenesis, the belief that life must have arisen from non-living things through a natural process. However, abiogenesis has never been observed. To the contrary, it has been shown numerous times that biogenesis is true, that only living things give rise to living things. That is, abiogenesis has been scientifically disproved. To persist in belief in abiogenesis, one must believe in something that clearly is unscientific.