What are fossils? How are they formed? Describe in brief two methods of determining the age of fossils. State any one role of fossils in the study of the progress of evolution.
What are fossils? How are they formed? Describe in brief two methods of determining the age of fossils. State any one role of fossils in the study of the progress of evolution.
Fossils: Fossils are the naturally preserved remains of organisms like plants and animals that existed on the earth a long time ago.
Formation of fossils:
- Fossils usually form when the organisms die and get buried due to different reasons.
- The bodies or remains of the organisms then get covered by ashes, sand, lava, or soil to form layers over them.
- These layers get hardened over time due to different factors like pressure.
- Each layer indicates the geologic time during which these organisms got buried.
Example:
- The organisms like invertebrates existing in the ocean died and got buried under the sand. These organisms remained in this sand since the gradual accumulation of more sand over them will form layers.
- After millions of years, dinosaurs got extinct and buried above these layers in which invertebrates were already buried. The same occurs to the bodies of the dinosaurs. Another layer containing fossils is thus formed.
- Exposure to conditions like rainfall etc can expose these fossils by removing the layer/s present above them.
Methods of determining the age of fossils:
1. Relative method:
- In this method, the distance of the fossil from the surface of the earth is used to estimate the age.
- The layer in which a fossil is buried or discovered represents the geologic time during which this organism existed.
- This means that the organism present at a deeper level or in a layer distant from the surface of the earth is older than the organism present in a layer closer to the surface of the earth.
- The fossil discovered from a top layer is more recent as compared to the one that is discovered from a bottom layer.
2. Carbon dating method:
- This method measures the ratio of the amount of the isotopes of the same element. In carbon dating, a radioactive isotope of carbon (C-14) present in a fossil is used to determine its age.
- The ratio of the isotopes in a fossil is compared to the ratio of the isotopes in the organisms present today to know the difference.
- C-14 is a radioactive isotope and is not absorbed by the organisms after their death, therefore, its amount is used to estimate the time of the death of the organism. There is a reduction in the radioactivity of this isotope after death.
- The decay in C-14 represents the period that has passed since the death of that organism. This means, more decay means more time has passed since the death and fossil is older as compared to another fossil in which the decay is lesser.
Importance of fossil study: The fossils provide the order of evolution of different species over time.
Example: Archeopteryx is an example of a fossil that has features of both birds (have feathers) and reptiles (have a long-tail). This is a connecting link between birds and reptiles. This fossil helps conclude that birds originated from reptiles.
Fossils: Fossils are the naturally preserved remains of organisms like plants and animals that existed on the earth a long time ago.
Formation of fossils:
- Fossils usually form when the organisms die and get buried due to different reasons.
- The bodies or remains of the organisms then get covered by ashes, sand, lava, or soil to form layers over them.
- These layers get hardened over time due to different factors like pressure.
- Each layer indicates the geologic time during which these organisms got buried.
Example:
- The organisms like invertebrates existing in the ocean died and got buried under the sand. These organisms remained in this sand since the gradual accumulation of more sand over them will form layers.
- After millions of years, dinosaurs got extinct and buried above these layers in which invertebrates were already buried. The same occurs to the bodies of the dinosaurs. Another layer containing fossils is thus formed.
- Exposure to conditions like rainfall etc can expose these fossils by removing the layer/s present above them.
Methods of determining the age of fossils:
1. Relative method:
- In this method, the distance of the fossil from the surface of the earth is used to estimate the age.
- The layer in which a fossil is buried or discovered represents the geologic time during which this organism existed.
- This means that the organism present at a deeper level or in a layer distant from the surface of the earth is older than the organism present in a layer closer to the surface of the earth.
- The fossil discovered from a top layer is more recent as compared to the one that is discovered from a bottom layer.
2. Carbon dating method:
- This method measures the ratio of the amount of the isotopes of the same element. In carbon dating, a radioactive isotope of carbon (C-14) present in a fossil is used to determine its age.
- The ratio of the isotopes in a fossil is compared to the ratio of the isotopes in the organisms present today to know the difference.
- C-14 is a radioactive isotope and is not absorbed by the organisms after their death, therefore, its amount is used to estimate the time of the death of the organism. There is a reduction in the radioactivity of this isotope after death.
- The decay in C-14 represents the period that has passed since the death of that organism. This means, more decay means more time has passed since the death and fossil is older as compared to another fossil in which the decay is lesser.
Importance of fossil study: The fossils provide the order of evolution of different species over time.
Example: Archeopteryx is an example of a fossil that has features of both birds (have feathers) and reptiles (have a long-tail). This is a connecting link between birds and reptiles. This fossil helps conclude that birds originated from reptiles.
