Give scientists clues about the kind of organisms that lived in an ancient environment

The answer is a fossil.

The fossil represents a preserved remain of an organism from the past and gives scientists clues about the kind of organisms that lived in an ancient environment.
Usually, hard tissue, such as bones and teeth or exoskeleton is much more preserved than soft tissue (organs, skin, etc.). Fossils become fossils by a process of mineralization. Hard tissues are more mineralized during life than organs. So it is no surprise that hard tissues take part in the process of mineralization and is preserved in fossils, unlike soft tissues