Fossils are fundamental to the geologic time scale. The names of most of the eons and eras end in zoic, because these time intervals are often recognized on the basis of animal life. Rocks formed during the Proterozoic Eon may have fossils of relative simple organisms, such as bacteria, algae, and wormlike animals
Solid - made up of tightly packed particles, which gives it a solid shape.
Gas - made up of very loose particles, giving it more freedom to roam around as a gas
Liquid - fills into whatever it gets put in, basically takes the shape of the object its in
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