mold: a soft green, gray, or black growth that develops on old food or on objects that have been left too long in warm, slightly wet places

fish: an animal that lives in water, is covered with scales, and breathes by taking water in through its mouth, or the flesh of these animals eaten as food

sponge: a soft substance that is full of small holes and can absorb a lot of liquid, and is used for washing and cleaning

footprint: the mark made by a person's or animal's foot

fossil: the shape of a bone, a shell, or a plant or animal that has been preserved in rock for a very long period

tar: a black substance, sticky when hot, used especially for making roads

mud: earth that has been mixed with water

trilobite: a simple, flat sea creature that lived in the earliest period of life on earth, with a hard outer layer and a body in three parts

carbon: a chemical element that exists in its pure form as diamond or graphite, and is an important part of other substances such as coal and oil, as well as being contained in all plants and animals

mineral: a valuable or useful chemical substance that is formed naturally in the ground

impression: a mark made on the surface of something by pressing an object into it

horseshoe: a U-shaped piece of metal that is attached to the bottom of a horse's hoof to protect it

cast: an object made by pouring hot liquid into a container and leaving it to become solid