Comment: 07:42 - 08:56 (01:14)
Source: Annenberg/CPB Resources - Earth Revealed - 17. Sedimentary Rocks: The Key to Past Environments
Keywords: "sedimentary rock", "chemical sedimentation", ocean, "biological activity", algae, coral, invertebrate, "calcium carbonate", shell, reef, "sea floor", limestone, fossil, chalk, plant, animal, life, "continental shelf", radiolaria, diatom, silica, chert, diatomite
Our transcription: Chemical sedimentation also takes place in the ocean.
Biological processes play a crucial role in triggering this phenomenon.
Algae, coral, and invertebrate organisms all utilize calcium carbonate in constructing shells and reefs.
When these organisms die, their carbonate hard parts accumulate on the sea floor to form limestone, one of the most common sedimentary rocks on Earth.
Limestones vary greatly in appearance from formations packed with large fossils to beds of chalk formed from the microscopic shells of plants and animals.
Life also contributes to the formation of sedimentary rocks other than limestone.
In the cool nutrient rich water near some continental shelves, radiolaria and diatoms thrive.
These suspended microscopic organisms use silica to make their shells.
When they die and settle to the sea floor, the silica accumulates to form layers of chert and diatomite.
Geology School Keywords