Question

Why are fossils never found in Igneous rocks?

• A. Because they are formed under the ocean.
• B. Because the intense heat of volcanic eruptions destroys any organic matter.
• C. Because they are too soft to hold fossils.
• D. Because they are only found deep within the Earth's core.

Answer 1

Answer:

B. Because the intense heat of volcanic eruptions destroys any organic matter.

Formation of Igneous Rocks and Fossil Preservation

Igneous Rocks Formation:

• Igneous rocks are formed from the cooling and solidification of molten rock material, which can be magma (beneath the Earth's surface) or lava (on the Earth's surface).

• The process involves extremely high temperatures, often exceeding 700 degrees Celsius (1292 degrees Fahrenheit).

• Examples of igneous rocks include granite, basalt, and obsidian.

Impact of Heat on Organic Matter:

• Fossils are the preserved remains or traces of ancient organisms (plants and animals).

• The process of fossilization typically requires the rapid burial of organic material in sediment, followed by mineralization over long periods.

• The intense heat associated with the formation of igneous rocks, especially from volcanic activity (lava flows, pyroclastic flows), would completely incinerate and destroy any organic matter.

• This extreme thermal degradation prevents the preservation of fossil structures.

Sedimentary Rocks and Fossilization:

• In contrast, fossils are commonly found in sedimentary rocks.

• Sedimentary rocks are formed from the accumulation and cementation of sediments (like sand, silt, and clay) over time, often in aquatic environments.

• These environments provide the necessary conditions for the preservation of organic remains, as the burial process occurs at much lower temperatures, allowing for gradual mineralization.

• Examples of sedimentary rocks where fossils are found include sandstone, shale, and limestone.

Metamorphic Rocks:

• Fossils are also rarely found in metamorphic rocks, which are formed when existing rocks (igneous, sedimentary, or other metamorphic rocks) are transformed by heat, pressure, or chemical reactions.

• While the heat in metamorphism might not be as extreme as in the initial formation of igneous rocks, it is often sufficient to deform or destroy delicate fossil structures.