Some people mistakenly believe that since we do not have direct access to the distant past we cannot learn much about it. Contemporary historians and archaeologists find current geography, geology, and climate to be rich in clues about a given region' s distant history. However, the more distant the period we are studying is, the less useful the study of the present becomes.
The principle that the passage illustrates is that astronomers often draw inferences about the earlier years of our solar system on the basis of recently collected data, but they have been able to infer comparatively little about the origin of our solar system.