Question

Which of the following is least likely to be found as a fossil? A. clam shell C. snail shell B. shark tooth D. jellyfish imprint

Short answer

Jellyfish imprint.

Step-by-step solution

Understanding Fossils

Fossils are the preserved remains or impressions of organisms from the past, usually found in sedimentary rock. The conditions that contribute to fossilization include rapid burial and the presence of hard parts like bones, shells, or teeth.

Analyzing Each Option

We consider the composition and structure of the objects. Clam shells and snail shells are made of calcium carbonate, which fossilizes well. Shark teeth are also composed of hard material (dentine and enamel), making them likely to fossilize. A jellyfish is mostly soft-bodied with no hard parts.

Determining the Least Likely Fossil

Soft-bodied organisms like jellyfish are less likely to fossilize because they lack the hard parts that are more resistant to decay and conducive to fossilization processes.

Final Decision

Given that clam shells, snail shells, and shark teeth have hard parts that improve fossilization chances, while jellyfish are soft-bodied, a jellyfish imprint is least likely to be found as a fossil.

Key concepts

Sedimentary Rock

Sedimentary rocks are a crucial component in the fossilization process. They are formed by the accumulation of sediments over time, usually in layers. These rocks provide the perfect environment for fossils to form because:

• They cover and protect remains quickly from scavengers and decay.
• They typically consist of sand, silt, or clay that are fine enough to capture and preserve detail.

The conditions in sedimentary rocks allow for the gradual mineralization of organic material, turning it into stone. These rocks are frequently found in areas that were once close to water bodies like rivers or seas, where sediments were rapidly deposited. Thus, finding fossils in sedimentary rocks is common due to these supportive conditions.

Soft-bodied Organisms

Soft-bodied organisms present a challenge when it comes to fossilization. They do not have hard parts like bones or shells, which makes them susceptible to complete decay before fossilization occurs. A soft-bodied organism like a jellyfish is primarily composed of delicate tissues that:

• Break down quickly when exposed to environmental conditions.
• Lack durable components that can withstand geological processes.

Without parts that can easily preserve, it is rare to find fossils of such organisms. However, under exceptional circumstances, impressions or imprints can be preserved in fine sediment before they decay entirely, but this is quite rare compared to organisms with hard parts.

Calcium Carbonate

Calcium carbonate is a substance that greatly aids in the fossilization of certain organisms. It is a chemical compound found in shells and some hard-shelled organisms, making these organisms excellent candidates for fossil formation. Here's why calcium carbonate plays a vital role:

• It is hard and durable, providing structural integrity to shells.
• Its mineral nature allows it to resist decay and disintegration over time.

When organisms with calcium carbonate are buried under sediment, their shells can gradually mineralize into rock, preserving their form for millions of years. This process makes clam and snail shells more likely to be found as fossils compared to organisms that lack such protective structures.

Preserved Remains

Preserved remains refer to the parts of an organism that have been saved from decay and have undergone fossilization. The most common preserved remains are hard structures like bones, shells, and teeth. The fossilization process can take several forms, such as:

• Petrification, where organic material is replaced by minerals.
• Impressions, where an organism leaves a mark or outline in the surrounding sediment.
• Molds and casts, formed when the organism decays, leaving a space filled later by minerals.

Preserved remains offer invaluable insights into ancient life, allowing scientists to study the morphology and sometimes even the behavior of extinct organisms. They create a tangible link to the past, helping us understand evolutionary processes and environmental change.