Final answer:
The inference that can be made about the earth layer without any fossils is that it is a metamorphic rock.
Step-by-step explanation:
The inference that can be made about the earth layer that doesn't contain any fossils is that it is a metamorphic rock. Metamorphic rocks are formed through physical and chemical alterations under high temperature and pressure, which would destroy any fossils present in the original rock. The fact that this layer doesn't contain any sedimentary structures and is very dark and fine-grained also supports the inference of it being a metamorphic rock.