Fossil: Difference between revisions
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The word '''fossil''' is derived from the Latin ''fossilis'', something dug up.<ref name="MacRae">MacRae, C.S. 1999. ''Life Etched in Stone: Fossils of South Africa''. The Geological Society of South Africa, Johannesburg.</ref> | The word '''fossil''' is derived from the Latin ''fossilis'', something dug up.<ref name="MacRae">MacRae, C.S. 1999. ''Life Etched in Stone: Fossils of South Africa''. The Geological Society of South Africa, Johannesburg.</ref> | ||
During the [[Middle Ages]], the term ‘fossil’ was used for any sample recovered from the Earth, including [[rocks]] and [[minerals]].<ref name="MacRae"/> Today, fossils are recognised as any record of ancient [[life]]. They can be actual remnants of an organism, or evidence of their behaviour.<ref name="MacRae"/> | During the [[Middle Ages]], the term ‘fossil’ was used for any sample recovered from the Earth, including [[rocks]] and [[minerals]].<ref name="MacRae"/> Today, fossils are recognised as any record of ancient [[life]]. They can be actual remnants of an organism, or evidence of their last behaviour.<ref name="MacRae"/> | ||
== Overview == | == Overview == | ||
Fossils represent a very small proportion of all the organisms which have ever lived. This is because fossils only form under specific conditions. [[Decomposition]] is a requirement for environments to function | Fossils represent a very small proportion of all the organisms which have ever lived. This is because fossils only form under specific conditions. [[Decomposition]] is a requirement for environments to function. It follows that [[fossilization]] represents a deviation from this natural process.<ref name="MacRae"/> | ||
Any [[plant]] or [[animal]] needs to pass through a number of stages in order to become a fossil.<ref name="Brett & Baird">Brett, C.E. & Baird, G.C. 1986. Comparative Taphonomy: A Key to Paleoenvironmental Interpretation Based on Fossil Preservation. ''PALAIOS'' '''1'''(3): 207-227.</ref> First, the organism must become deposited in sediment. Once it is buried, it may begin to undergo diagenetic processes. Diagenesis is simply any change, chemical or physical, which occurs in an organism after burial.<ref name="Brett & Baird"/> Such changes are necessary for preservation because organic matter will not survive for long before it is decomposed. However, older fossils are more likely to have been modified by diagenetic processes, and thus, to be a less accurate copy of the original”.<ref name="Allison & Briggs">Allison, P.A. & Briggs, D.E.G. 1991. ''Taphonomy: Releasing the Data Locked in the Fossil Record''. Plenum Press, New York.</ref> | Any [[plant]] or [[animal]] needs to pass through a number of stages in order to become a fossil.<ref name="Brett & Baird">Brett, C.E. & Baird, G.C. 1986. Comparative Taphonomy: A Key to Paleoenvironmental Interpretation Based on Fossil Preservation. ''PALAIOS'' '''1'''(3): 207-227.</ref> First, the organism must become deposited in sediment. Once it is buried, it may begin to undergo [[diagenesis|diagenetic]] processes. Diagenesis is simply any change, chemical or physical, which occurs in an organism after burial.<ref name="Brett & Baird"/> Such changes are necessary for preservation because organic matter will not survive for long before it is decomposed. However, older fossils are more likely to have been modified by diagenetic processes, and thus, to be a less accurate copy of the original”.<ref name="Allison & Briggs">Allison, P.A. & Briggs, D.E.G. 1991. ''Taphonomy: Releasing the Data Locked in the Fossil Record''. Plenum Press, New York.</ref> | ||
A more detailed explanation of how and why fossils form can be found in the article [[fossilization]]. | A more detailed explanation of how and why fossils form can be found in the article [[fossilization]]. | ||
== Different types of fossils == | == Different types of fossils == | ||
{{Image|Ichnogenus Diplocreterion - MacRae.jpg|right|300px|The ichnogenus ''Diplocreterion'' created these burrows in loose sand. It is called an ichnogenus because fossils of the actual animal responsible have not been found in conjunction with the burrows. Nonetheless, this is still a fossil as it preserves a record of ancient life.}} | {{Image|Ichnogenus Diplocreterion - MacRae.jpg|right|300px|The ichnogenus ''Diplocreterion'' created these burrows in loose sand. It is called an ichnogenus, because fossils of the actual animal responsible have not been found in conjunction with the burrows. Nonetheless, this is still a fossil as it preserves a record of ancient life.}} | ||
Fossils can be formed in a number of ways. The mineral replacement of shell or bone is called petrification, because it turns organic material into stone.<ref name="McCarthy & Rubidge">McCarthy, T. & Rubidge, B. 2005. ''The Story of Earth and Life: A southern African perspective on a 4.6-billion-year journey''. Struik Publishers, Cape Town.</ref> | Fossils can be formed in a number of ways. The mineral replacement of shell or bone is called [[petrification]], because it turns organic material into stone.<ref name="McCarthy & Rubidge">McCarthy, T. & Rubidge, B. 2005. ''The Story of Earth and Life: A southern African perspective on a 4.6-billion-year journey''. Struik Publishers, Cape Town.</ref> | ||
An organism can leave a mould behind when it decays, preserving surface detail in the surrounding sediment. If the mould later fills with sediment, an external replica of the organism is created called a cast. A cast does not preserve the internal structure of the original organism.<ref name="MacRae"/> Trace fossils are not remnants of an organism itself, but some record of its behaviour. Tracks, burrows, | An organism can leave a mould behind when it decays, preserving surface detail in the surrounding sediment. If the mould later fills with sediment, an external replica of the organism is created called a cast. A cast does not preserve the internal structure of the original organism.<ref name="MacRae"/> Trace fossils are not remnants of an organism itself, but some record of its last behaviour. Tracks, burrows, [[coprolite]]s (fossil faeces) and [[stone tools]] are all examples of trace fossils. | ||
Any animal or plant has the potential to become a fossil, although this depends to a certain degree on its makeup. Soft-bodied organisms are preserved, although they are much rarer than fossils of hard parts. Plant fossils are usually not intact, because various structures of a plant are inclined to fall off during its lifetime. This creates separate fossils of the different parts.<ref name="McCarthy & Rubidge"/> The most common fossils are bones and teeth.<ref name="Shipman">Shipman, P. 1981. ‘’Life History of a Fossil: An Introduction to Taphonomy and Paleoecology’’. Harvard University Press, England.</ref> | Any animal or plant has the potential to become a fossil, although this depends to a certain degree on its makeup. Soft-bodied organisms are preserved, although they are much rarer than fossils of hard parts. Plant fossils are usually not intact, because various structures of a plant are inclined to fall off during its lifetime. This creates separate fossils of the different parts.<ref name="McCarthy & Rubidge"/> The most common fossils are bones and teeth.<ref name="Shipman">Shipman, P. 1981. ‘’Life History of a Fossil: An Introduction to Taphonomy and Paleoecology’’. Harvard University Press, England.</ref> | ||
Revision as of 08:15, 20 October 2010
The word fossil is derived from the Latin fossilis, something dug up.[1] During the Middle Ages, the term ‘fossil’ was used for any sample recovered from the Earth, including rocks and minerals.[1] Today, fossils are recognised as any record of ancient life. They can be actual remnants of an organism, or evidence of their last behaviour.[1]
Overview
Fossils represent a very small proportion of all the organisms which have ever lived. This is because fossils only form under specific conditions. Decomposition is a requirement for environments to function. It follows that fossilization represents a deviation from this natural process.[1] Any plant or animal needs to pass through a number of stages in order to become a fossil.[2] First, the organism must become deposited in sediment. Once it is buried, it may begin to undergo diagenetic processes. Diagenesis is simply any change, chemical or physical, which occurs in an organism after burial.[2] Such changes are necessary for preservation because organic matter will not survive for long before it is decomposed. However, older fossils are more likely to have been modified by diagenetic processes, and thus, to be a less accurate copy of the original”.[3] A more detailed explanation of how and why fossils form can be found in the article fossilization.
Different types of fossils
Fossils can be formed in a number of ways. The mineral replacement of shell or bone is called petrification, because it turns organic material into stone.[4] An organism can leave a mould behind when it decays, preserving surface detail in the surrounding sediment. If the mould later fills with sediment, an external replica of the organism is created called a cast. A cast does not preserve the internal structure of the original organism.[1] Trace fossils are not remnants of an organism itself, but some record of its last behaviour. Tracks, burrows, coprolites (fossil faeces) and stone tools are all examples of trace fossils.
Any animal or plant has the potential to become a fossil, although this depends to a certain degree on its makeup. Soft-bodied organisms are preserved, although they are much rarer than fossils of hard parts. Plant fossils are usually not intact, because various structures of a plant are inclined to fall off during its lifetime. This creates separate fossils of the different parts.[4] The most common fossils are bones and teeth.[5]
Famous Fossils
There are some very famous fossil hominins from South Africa, namely the Taung Child, Mrs Ples and Little Foot.
References
- ↑ 1.0 1.1 1.2 1.3 1.4 MacRae, C.S. 1999. Life Etched in Stone: Fossils of South Africa. The Geological Society of South Africa, Johannesburg.
- ↑ 2.0 2.1 Brett, C.E. & Baird, G.C. 1986. Comparative Taphonomy: A Key to Paleoenvironmental Interpretation Based on Fossil Preservation. PALAIOS 1(3): 207-227.
- ↑ Allison, P.A. & Briggs, D.E.G. 1991. Taphonomy: Releasing the Data Locked in the Fossil Record. Plenum Press, New York.
- ↑ 4.0 4.1 McCarthy, T. & Rubidge, B. 2005. The Story of Earth and Life: A southern African perspective on a 4.6-billion-year journey. Struik Publishers, Cape Town.
- ↑ Shipman, P. 1981. ‘’Life History of a Fossil: An Introduction to Taphonomy and Paleoecology’’. Harvard University Press, England.