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Geology is the Way


Frustula of a fossil diatom (Amphora sp.), consisting of two valves. Scanning Electron Microscope image by Berezovska.

Diatoms are single-celled algae, specifically microalgae, that live in the Earth’s oceans, waterways, and soils. They are autotrophic organisms that live by photosynthesis in the photic zone – in the first 200 meters of the water column.  Even if these organisms are very tiny, ranging in size between 2 and 200 micrometers (< 0.2 mm), they constitute a non negligible part of the biomass and are responsible for the production of 20 to 50% of the Earth’s oxygen each year. Diatom cells are surrounded by a shell consisting of two symmetric parts that is called frustule and consists of amorphous hydrated silica. After their death, their silica shells accumulate on the ocean floors forming deposits of diatomites or diatomitic cherts. Diatoms occur everywhere in oceans, but they are concentrated close to the arctic regions, where they are currently producing thick marine deposits of siliceous ooze. Earliest known diatoms date back to the early Jurassic, but sedimentary evidence suggest that the might have already been present since the early Triassic.

Above: Footage of a living Navicula diatom by TheMicrobiology09 (light microscope)

Light microscope image of diatom-rich siliceous sediment. Accumulations of biogenic silica, consisting of shells of diatoms produces diatomites – a type of chert. Field of view is approximately 1.13 by 0.69 mm. Photo by Zephyris.

Alldredge, A. L., & Gotschalk, C. C. (1989). Direct observations of the mass flocculation of diatom blooms: characteristics, settling velocities and formation of diatom aggregates. Deep Sea Research Part A. Oceanographic Research Papers36(2), 159-171.
Falasco, E., Bona, F., Badino, G., Hoffmann, L., & Ector, L. (2009). Diatom teratological forms and environmental alterations: a review. Hydrobiologia623(1), 1-35.
Lewin, J. C. (1961). The dissolution of silica from diatom walls. Geochimica et Cosmochimica Acta21(3-4), 182-198.
Ross, R., Cox, E. J., Karayeva, N. I., Mann, D. G., Paddock, T. B. B., Simonsen, R., & Sims, P. A. (1979). An amended terminology for the siliceous components of the diatom cell.
Simonsen, R. (1987). Atlas and catalogue of the diatom types of Friedrich Hustedt.


See also

Detrital and Authigenic Minerals
Sedimentary Structures
Sedimentary Rocks


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