Multiple Choice
Which of the following can be learned about a species from studying their fossilized skeletons?
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24. History of Life on Earth
The Fossil Record
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What happens to the soft parts of organisms when cast fossils form?
A
They are replaced by minerals and become part of the fossil.
B
They are compressed into coal.
C
They remain intact inside the cast fossil.
D
They usually decay and are not preserved.
Verified step by step guidance1
Understand the concept of cast fossils: Cast fossils are formed when an organism's hard parts, such as bones or shells, leave an impression in sediment, and minerals fill this impression to create a replica of the original structure.
Recognize the fate of soft parts in fossilization: Soft tissues of organisms are typically not preserved because they are more prone to decay due to microbial activity and environmental conditions.
Clarify why soft parts decay: Soft tissues lack the durability of hard parts like bones or shells, and they decompose quickly unless exceptional preservation conditions exist, such as rapid burial or anoxic environments.
Differentiate between cast fossils and other fossil types: Cast fossils specifically involve the mineralization of impressions left by hard parts, whereas other fossil types, like carbonized fossils, may preserve some organic material under specific conditions.
Conclude that soft parts usually decay: In the process of cast fossil formation, the soft parts of organisms decay and are not preserved, leaving only the mineralized cast of the hard parts.
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