Argumentation skills and scientific reasoning are continually discussed as being essential for the 21st century. In our contribution, we will focus on how laypeople judge the plausibility of science-based arguments. We will first work out different layers of scientific knowledge that might come into play when individuals need to evaluate science-based arguments. We will argue that, in general, science-based arguments can be understood and judged by criteria on three layers of scientific knowledge: 1) the ontology, 2) the methods and sources, and 3) the social practices required for the generation and justification of the argument. Furthermore, we will show that these layers could be of varying specificity. We will elaborate the three layers of scientific knowledge by focusing on a common situation in everyday science evaluation: competing arguments about a science-based topic. We will provide empirical evidence on studies we have conducted indicating that laypersons’ explanations for contradictions among scientists refer to the three layers we have outlined. Subsequently, we will argue that science-based arguments often need to be judged without a full understanding, and that the different layers may be differentially available to laypersons (i.e. differently easy to understand). Finally, we will discuss the theoretical and educational implications.