Notes

Coal is the remains of plants that died in ancient swamps. When the plants died and fell into the water, the oxygen content of the water prevented them from decaying completely and layers of peat formed. Over time, the peat was dried and compressed into coal.


No, not all rocks contain fossils. Dead organic matter usually is destroyed quickly by scavengers or bacteria. Only when the organism was quickly covered could it be preserved. Hard parts of organisms were less apt to be consumed or eroded by weather.


Some fossil organisms called index fossils have well documented ages. If these fossils are found in a rock layer, the approximate age of that rock can be inferred.


A carbon film fossil forms when sediment covers an organisms. As it decays, gases escape the organisms, leaving a thin film of carbon that preserves part of the organism.


Fossils form through the process of mineral replacement beginning when an organism dies and is buried. Groundwater seeps around the organism, and the minerals in the water gradually replace the minerals in the hard parts of the organism. Over time these minerals turn into a stone replica of an organism.


Trace fossils are not the preserved remains of ancient organisms. Instead, they provide information about the activities of the organisms. Examples are fossilized footprints and burrows.



Both molds and casts copy the shape of the organism. A mold is a hollow area in the sediment in the shape of the organism. A cast is a solid copy of the organism.


Jellyfish are invertebrates, so they do not have the hard body parts that favor fossilization.



Scientists can use fossils to learn about past environments. By studying to the fossilized remains of ancient organisms, scientist can infer what type of climate they lived in by comparing them to similar organisms alive today.