Hello! The word "in" in this context is expressing that something (in his case information) is or appears to be enclosed or surrounded by something else. "The objects the archeologists discover, on the other hand, tell us nothing directly in themselves." means that the objects that are found by the archeologists don't give information directly. So "in" is used as the preposition to indicate that the information is not learned directly from the objects found - so the objects don't show the information directly. Also, I changed "tells" to "tell" because the subject is plural, so the verb has to be in the plural form as well. For example, "one person tells us something" and, " many people tell us something". I hope that helps!

I think neither - the objects on their own tell us nothing, but when put into combination with other things they can provide more information.