One well-known example would be the Cosmic Microwave Background, which was (and still can be) observed (but not created in the lab) and which is considered evidence which confirms the Big Bang theory. This "mere observation" was regarded as sufficiently persuasive that it plunged the Steady State theory into oblivion.
Yet another example would be the striking fact (a "mere observation" not reproduced in the lab) that all known fossils, when arranged by age and structure, form a tree structure, giving the definite appearance of common descent. Interestingly, there are no fossils that contradict such appearance -- such as a mammal in the precambrian period. (The absence of such anachronisms may be viewed as "gaps" in the creation science theory.) Further confirmation of the theory of common descent is that the DNA evidence, where available, also supports the picture presented by the fossil record. (So far, no lab has attempted to re-create all species on earth, so there are those who aren't persuaded by the observable evidence.)