science

Microbialite

Microbialite is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Microbialite rather than just read about it. In short: Microbialite is a benthic sedimentary deposit made of carbonate mud (particle diameter less than 5 μm) that is formed with the mediation of microbes. The constituent carbonate mud is a type of automicrite (or authigenic carbonate mud); therefore, it precipitates in situ instead of being transported and deposited.

Key takeaways

Microbialite belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Microbialite to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Microbialite from memory before moving on to harder problems.

Reference excerpt

Microbialite is a benthic sedimentary deposit made of carbonate mud (particle diameter less than 5 μm) that is formed with the mediation of microbes. The constituent carbonate mud is a type of automicrite (or authigenic carbonate mud); therefore, it precipitates in situ instead of being transported and deposited. Being formed in situ, a microbialite can be seen as a type of boundstone where reef builders are microbes, and precipitation of carbonate is biotically induced instead of forming tests, shells or skeletons. Microbialites can also be defined as microbial mats with lithification capacity. Bacteria can precipitate carbonate both in shallow and in deep water (except for Cyanobacteria) and so microbialites can form regardless of the sunlight. Microbialites are the foundation of many lacustrine ecosystems, such as the biosystem of the Great Salt Lake with its millions of migratory birds or, serving in the Alchichica Lake as nurseries for axolotl (Ambystoma taylori) and a variety of fish. Microbialites were very important to the formation of Precambrian and Phanerozoic limestones in many different environments, marine and not. The most favorable time for stromatolite proliferation was from 2800 Ma to 1000 Ma when stromatolites were the main constituents of carbonate platforms. The three types of microbialites are stromatolites, thrombolites, and leiolites.

Classification Microbialites can have three different fabrics:

Stromatolitic: microbialite layered, laminated or agglutinated to form a stromatolite. Thrombolitic: microbialite with a clotted peloidal fabric if observed with a petrographic microscope. The density of peloids is variable. At the scale of the hand sample, the rock shows a dendritic fabric, and can be named thrombolite. Leiolitic: a microbialite with no layering nor clotted peloidal fabric. It is only made of a dense automicrite.

Evolution Microbialites played an important role in the evolution of the Earth's atmosphere, since they were ancestral niches where the first microbial metabolisms capable of releasing oxygen arose. Microbialites saturated coastal systems and later the primitive atmosphere with oxygen, changing it from a reduced state to an oxidized state. The fossil microbialites (also called stromatolites) of the Precambrian and Phanerozoic are one of the first evidences of communal life. The oldest microbialites are dated at 3.5 billion years. Fossil evidence suggests that microbialite-producing organisms were a very abundant life form from the early Archaean to the late Proterozoic, until their communities decreased due to the predation of foraminifera and other eukaryotic microorganisms. Microbialites again became common briefly after the Permian-Triassic extinction event.

Formation of microbialites The formation of microbialites is complex and is a continuous process of precipitation and dissolution, where different microbial metabolisms are coupled and a high saturation index (SI) of ions in water is present. Microbialites have two possible genesis mechanisms: 1) Mineral precipitation: is the main formation process of microbialites and it can be due to inorganic precipitation or to the passive influence of microbial metabolisms. There can also be precipitation due to saturation of the microenvironment when extracellular polymeric substances (EPS) are rapidly degraded, increasing ion saturation. 2) Trapping and binding: when the microbial community includes mineral particles of the environment that adhere to the extracellular polymeric substances (EPS). This process is very popular, since it was described in modern microbialites of Shark Bay (Australia) and Bahamas, but it has been shown to be very uncommon throughout the 3500 million year long geological history of microbialites.

Modern microbialites distribution Living modern microbialites (less than 20,000 years old) are rare and can be found confined to places such as:

Crater lakes: Blue Lake (Australia), Lake Satonda (Indonesia), Lake Dziani (Mayotte Island), Lake Alchichica (Mexico), Lake Vai Lahi and Lake Vai Sii (Tonga), Lake Salda (Turkey) Saline / hypersaline lakes / lagoons: Pyramid Lake and Great Salt Lake (United States), Lagoa Salgada and Lagoa Vermelha (Brazil), Lake Van (Turkey), Brava Lagoon and Tebinquicho Lagoon (Chile), Laguna Negra, Catamarca (Argentina), Storr Lake (Bahamas), Laguna Pirata (Venezuela), Laguna Providencia (Puerto Rico) Alkaline lakes: Lake Thetis (Australia), Lake Sarmiento (Chile), Lake Nuoertu and Lake Huhejaran (China), Mono Lake (United States), Lake Turkana (Kenya), Lake Petukhovskoe (Russia) Freshwater lakes / lagoons: Lagunas de Ruidera (Spain), Bacalar and Cuatro Cienagas (Mexico), Lake Richmond (Australia), Pavilion Lake (Canada), Green Lake (United States) Alkaline pools: Four swamp blue pools (Mexico) Abandoned open mines: Clinton Creek (Canada), Rio Tinto (Spain) Hot springs: Little Hot Creek (United States) Marine / Estuary / Estuary Systems: Shark Bay, Australia, Highbourne Cay (Bahamas), Tikehau (French Polynesia),Cayo Coco (Cuba), Lake Clifton, Western Australia. Ice-covered Antarctic lakes: Lake Joyce (McMurdo Dry Valleys)

Composition Microbialites are built up with layers of some organic component and of some mineral. The organic component is an elaborate microbial mat where different communities of microorganisms interact according to different metabolisms and create a micro-niche where oxygenic and anoxygenic phototrophic organisms coexist: nitrogen fixers, sulfur reducers, methaneotrophs, methanogens, iron oxidizers, and a large number of heterotrophic decomposers. The mineral component is composed of carbonates, generally calcium carbonate or magnesium carbonates such as hydromagnesite, although there may also be sintered silicones, that is, silicates; and include mineral forms of sulfur, iron (pyrite) or phosphorus. Carbonate is usually a type of autogenic automicrite, therefore it precipitates in situ. Microbialites can be viewed as a type of biogenic sedimentary rock where the reef builders are microbes and carbonate precipitation is induced. Microorganisms can precipitate carbonate in both shallow and deep waters

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Microbialite

Start with the simplest possible case. Write down what Microbialite claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Microbialite before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Microbialite ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Microbialite

In research: Microbialite appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Microbialite in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Microbialite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Limestone, Sedimentology, Stromatolites, so understanding it makes those chapters shorter.
In everyday life: Look for Microbialite outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Microbialite in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Microbialite means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Microbialite out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Microbialite in simple terms?

Why does Microbialite matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Microbialite?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Microbialite.