Seventy-two Internet documents promoting creationism, intelligent design (I.D.), or evolution were selected for analysis. The primary goal of each of the 72 documents was to present arguments for creationism, I.D., or evolution. We first identified all arguments in these documents. Each argument was then coded in terms of both argument type (appeal to authority, appeal to empirical evidence, appeal to reason, etc.) and argument topic (age of earth, mechanism of descent with modification, etc.). We then provided a quantitative summary of each argument type and topic for each of the three positions. Three clear patterns were revealed by the data. First, websites promoting evolution were characterized by a narrow focus on appeals to empirical evidence, whereas websites promoting creationism and I.D. were quite heterogeneous in regards to argument type. Second, websites promoting evolution relied primarily on a small number of empirical examples (e.g., fossils, biogeography, homology, etc.), while websites promoting creationism and I.D. used a far greater range of arguments. Finally, websites promoting evolution were narrowly focused on the topic of descent with modification. In contrast, websites promoting creationism tackled a broad range of topics, while websites promoting I.D. were narrowly focused on the issue of the existence of God. The current study provides a quantitative summary of a systematic content analysis of argument type and topic across a large number of frequently accessed websites dealing with origins. The analysis we have used may prove fruitful in identifying and understanding argumentation trends in scientific writing and pseudo-scientific writing.