* Heat and Pressure: Metamorphism involves intense heat and pressure. These conditions cause the original minerals in the rock to recrystallize and change their structure. Fossils, often made of softer materials like bone or shell, are unable to withstand this transformation.
* Chemical Reactions: The heat and pressure also trigger chemical reactions that can dissolve or alter the fossil's composition.
* Recrystallization: As minerals recrystallize, they can grow larger and interlock, effectively obliterating any existing fossil structures.
However, there are some exceptions:
* Low-grade metamorphism: In some cases, very low-grade metamorphism, where the heat and pressure are relatively mild, might allow some fossils to survive with minimal distortion.
* Hardened fossils: Fossils that were originally made of hard, durable materials like some shells or teeth might withstand some degree of metamorphism.
How fossils form in sedimentary rock:
Fossils are typically found in sedimentary rocks because these rocks form under conditions that favor preservation. Here's how it works:
1. Organism dies: An organism dies and its remains are buried quickly by sediment.
2. Sedimentary layers: Over time, more sediment accumulates, burying the organism's remains deeper.
3. Pressure and minerals: The weight of the overlying sediment compresses the layers, and minerals dissolved in groundwater seep into the remains, replacing the original material with durable minerals like silica or calcite.
4. Fossil formation: The hardened remains become a fossil, preserving the shape and structure of the original organism.
So, while fossils are rarely found in metamorphic rock, their presence in sedimentary rocks provides valuable information about the history of life on Earth.
