1. waning - occurs after a full moon, when the amount of the moon's lighted side that can be seen becomes smaller.
2. trilobite - organism that lived hundreds of millions of years ago and is considered an index fossil of the Paleozoic era.
3. sori - spore-producing structures on the undersides of fern fronds.
4. sill - intrusive igneous rock body that forms when magma is squeezed into a crack and hardens.
5. prothallus - fern gametophyte, which can make its own food, absorb water and nutrients, and has both male and female reproductive structures
