Fossils are preserved imprints or traces of plants and animals. For example, imprints of plants or footprints from long ago are sometimes found preserved in rocks. You might also find fossilized things like bones, teeth, wood, and even droppings coprolites. Many of these fossils are formed when an animal or plant dies and is covered by layers of mud that, over time, turn to rock. This is why we find most fossils in sedimentary rock. In the case of bones, teeth, wood and droppings, minerals from the mud and soil slowly replace the organic matter in these things to create something that is mineralized and hard like rock.
In the case of petrified wood, when a tree dies in a wet area, water fills the small holes in the wood and deposits minerals that harden, turning the wood to rock. An imprint fossil is the outline of a plant or animal that has been left behind in a rock.
Add 1 Tablespoon water to the cup and stir until the plaster resembles thick frosting. Add an additional teaspoon of water as needed to achieve the correct consistency. Scoop out the plaster into the bottom of the Petri dish or lid. Gently tap the container on the table to allow the plaster to evenly spread out. Gently press an artificial plant leaf into the plaster, being careful not to submerge it.
Imprint fossils are also known as impression fossils. They do not contain any carbon material. Imprint fossils include coprolites fossilized feces , footprints, plants or tracks. Imprint fossils are formed in clay and silt sediment.
These sediments are fine-grained and moist and can hold onto an imprint for a long period of time. Imprint fossils are formed from an organism moving in some way, leaving behind a trace or track. Plants can also leave imprint fossils when they are covered by sediment. The leaf tissue degrades, leaving an imprint of where the leaf once was. Imprint fossils can give information about an organism's activity and the type of ecosystem that existed where the fossil was found.
Body fossils include molds and casts. A mold is the imprint left by the shell on the rock that surrounded it. An external mold is a mold of the outside of the shell. Each time we break a shell or bone out of the rock, an external mold is left behind. Molds of the underside of shell may be left on the surface of rock that formed when sand or mud filled the inside of the shell. These are called internal molds. Casts are replicas of the shell or bone that are formed from external or internal molds.
Casts can be produced naturally, but paleontologists can also produce casts from molds with latex rubber or even modeling clay.
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