What is "nonrigorous"

Usage examples of "nonrigorous".

Given the questions that still existed concerning the early atmosphere of the planet and the age and nature of the first living organisms, given the factors not yet taken into account (there are always factors not yet taken into account), given the relative speed with which complicated molecular systems developed and the nonrigorous estimates of the time involved for these designs to elaborate themselves, it seemed to Maurice Wu that an element of poetic truth might be contained in the speculation that humans and their precursors filled that huge primordial blank in the fossil record (a blank just beginning to be systematically roughed-in).