Fossils
Lesson objectives:
- By the end of this lesson, the student should be able to:
1- Define the concept of fossils.
2- Give different examples of fossils.
3- Show the types of fossils.
4- Determine the ways of fossils formation.5- Design a cast of a candle.
6- Design models of cast and mold.
7- Compare between mold and trace.
8- Give examples of complete body fossils.
9- Conclude the concept of petrification and petrified fossils.
10- Explain how the petrified woods are formed.
11-Mention the importance of studying fossils.
12-Calculate the age range of some fossils.
113-Appreciate the importance of the discovery of fossils.
14-Take personal decisions to protect fossils.
1-Fossil concept :
Traces and remains of the old living organisms that are preserved in sedimentary rocks are known as fossils.
2-Types of fossils and ways of formation
First type : Fossil of a complete body
- Complete body fossil was formed when the organism died and was buried fast in a medium that preserved it from decomposition as in the case of snow or amber. It keeps the whole shape and all the details of the body.
Examples of a complete body fossil:
1-Mammoth fossil :
A snow avalanche occurred in Siberia 25000 years ago.
It caused the death of mammoth animal, which were
It caused the death of mammoth animal, which were
also buried immediately in the snow.
When the first mammoth fossil was discovered in the last
century, it was complete as the whole shape, and all hair,
flesh and food in its bowels are all still completely preserved
century, it was complete as the whole shape, and all hair,
flesh and food in its bowels are all still completely preserved
2-Amber fossil :
During some old geologic periods, there were common
pine trees. These trees secreted resinous matter. This
matter covered insects, After the resinous mater had been solidified it was changed into amber and preserved the bodies of these organisms from decaying.
Second type : mold
The hardened plaster of Paris forms a solid mold of the metal mold.
- Formation of a solid mold
1- When a snail dies it falls on the sea floor and is buried in sediments.
2- The sediments fill up the shell,cavities and is solidified as the time passes
3-The shell could decompose completely, leaving a rock
mold carrying the internal details of the snail.
Third type : cast
A replica of the original outer shell shape is formed and it is known as cast.
Fourth type : Petrified fossils
A type of fossils where the minerals can replace the organic matter of organism part by
part without changing the shape, for examples:
Petrified wood-Dinosaur's tooth-Dinosaur's eggs
*Petrified woods look like rocks but they are fossils because they give us details about
once living old plant.
once living old plant.
*Petrified wood was formed by replacing , part by part, of the original wood material by silica, and this is known as “petrification”
Importance of fossils:
*Fossils are important because they help in:
1-Age determination of sedimentary rocks Fossils of the organisms that lived a short period of time in the past and became extinct are known as index fossils. They indicate the age of sedimentary rocks, because the age frocks is the same age of fossils extisted in them.
2-Figuring out the environmentalism:
Fossils give an idea about the environment in which they lived during the old geological ages.
3- Studying life evolution
4-Petroleum exploration: When searching for petroleum, geologists take samples from the rocks of the exploratory wells. These sample are studied microscopically. If they contain micro fossils like this could be a good indication of the age of the rocks from
which they were taken. and the suitable conditions for petroleum formation.
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