Answer:
The living organisms of the past.
Minerals more abundant in the soil of the past.
Step-by-step explanation:
Sedimentary rocks are formed by mineral and organic particles that were united by erosion. So, this particles bring useful information about some variables from the past that help to estimate age of existence and an idea of how was life back then.
A huge example are fossils, these are studied by palaeontologists, to study animals that existed before.