1. Source of Organic Matter:
* Plants: When plants die, their remains (leaves, stems, roots) accumulate on the ground or in water bodies. Over time, these decompose partially, creating organic matter like peat.
* Animals: Animal bones, shells, and even feces contribute to the organic matter that eventually becomes part of sediment.
2. Formation of Sediment:
* Weathering and Erosion: The organic matter from plants and animals is broken down further by weathering (rain, wind, ice) and erosion, creating smaller particles.
* Transportation and Deposition: These particles are transported by wind, water, or ice and eventually deposited in low-lying areas like lakes, oceans, or riverbeds.
3. Compaction and Cementation:
* Burial and Compaction: Over millions of years, new layers of sediment accumulate, burying the earlier layers. The weight of these layers compresses the sediment, squeezing out water and air.
* Cementation: Minerals dissolved in groundwater seep into the compacted sediment. These minerals crystallize and act like glue, binding the sediment particles together.
4. Formation of Sedimentary Rocks:
* Organic Rocks: If the organic matter is abundant, it can become the primary component of the rock. For example:
* Coal: Formed from compressed and carbonized plant remains.
* Oil and Natural Gas: Formed from microscopic marine organisms buried in sediment.
* Biogenic Rocks: Sedimentary rocks formed from the remains of organisms:
* Limestone: Formed from the calcium carbonate skeletons of marine organisms like corals and shellfish.
* Fossiliferous Limestone: Limestone containing fossilized remains of plants and animals.
In summary, plants and animals contribute to the formation of sedimentary rocks by:
* Providing organic matter that becomes sediment.
* Leaving behind mineralized remains like shells and bones.
* Influencing the chemical environment that affects the cementation process.
It's important to remember that sedimentary rocks are formed over extremely long periods, and the process involves the complex interplay of various geological factors.
