Because a cap is something on top like the armour
You failed to include the picture that goes with the question. However, the oldest fossils will be the fossils in the oldest layer, which is the lowest layer of sediment. Sedimentary rock forms as mud and silt pile up over thousands and millions of years. The layers of sediment harden and become rock. Organisms that are trapped in those layers become fossils as additional layers pile on top of them, forming new layers of sediment.
A natural or artificial body that revolves around a celestial body of greater mas is called a Satellite<span />
