Stromatolites



Stromatolites (from Greek strōma, mattress, bed, stratum, and lithos, rock) are defined as "attached, lithified sedimentary growth structures, accretionary away from a point or limited surface of initiation." A variety of stromatolite morphologies exist including conical, stratiform, branching, domal, and columnar types. Stromatolites are commonly thought to have been formed by the trapping, binding, and cementation of sedimentary grains by microorganisms, especially cyanobacteria (formerly known as blue-green algae). However, very few ancient stromatolites actually contain fossilized microbes. While features of some stromatolites are suggestive of biological activity, others possess features that are more consistent with "abiotic" (non-organic) precipitation. Finding reliable ways to distinguish between biologically-formed and abiotic (non-biological) "stromatolites" is an active area of research in geology.

Stromatolites were much more abundant on the planet in Precambrian times. While older, Archean fossil remains are presumed to be colonies of single-celled blue-green bacteria, younger (that is, Proterozoic) fossils may be primordial forms of the eukaryote chlorophytes (that is, green algae). One genus of stromatolite very common in the geologic record is Collenia.

Prior to 2.4 billion years ago, the earth's atmosphere was rich in carbon dioxide. However, the Precambrian air lacked the oxygen that sustains the complex multicellular life that has evolved since the "Cambrian explosion" 540 million years ago. Stromatolites in the fossil record decline sharply in both diversity and number during the late Proterozoic eon, although they are present, but not common, in Paleozoic era strata. Today, stromatolites are quite uncommon in marine environments, and thus are called "living fossils."

Their former abundance may be because there were no burrowing or grazing animals back during the Precambrian to destabilize sediments and consume growing microbial mats, thereby favoring the preservation of these microbialites. Also, changing chemical conditions in the ocean during this time could be responsible for the precipitation of non-biological stromatolites through the growth of tiny crystals.

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Modern stromatolites in Shark Bay, Western Australia.
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Stromatolites at Lake Thetis, Western Australia.
While prokaryotic cyanobacteria themselves reproduce asexually through cell division, they were instrumental in priming the environment for the evolutionary development of more complex eukaryotic organisms. Cyanobacteria are thought to be largely responsible for increasing the amount of oxygen in the primeval earth's atmosphere through their continuing photosynthesis.

Cyanobacteria use water, carbon dioxide, and sunlight to create their food. The byproducts of this process are oxygen and calcium carbonate (lime). A layer of mucous often forms over mats of cyanobacterial cells. In modern microbial mats, debris from the surrounding habitat can become trapped within the mucous, which can be cemented together by the calcium carbonate to grow thin laminations of limestone. These laminations can accrete over time, resulting in the banded pattern common to stromatolites. The domal morphology of biological stromatolites is the result of the vertical growth necessary for the continued infiltration of sunlight to the organisms for photosynthesis.

Modern stromatolites are mostly found in hypersaline lakes and marine lagoons where extreme conditions exclude animal grazing. One such location is Hamelin Pool Marine Nature Reserve, Shark Bay in Western Australia where excellent specimens are today observed, and another is Lagoa Salgada, state of Rio de Janeiro, Brazil, where modern stromatolites can be observed as bioherm (domal type) and beds. Fresh-water stromatolites can be found in Cuatro Ciénegas, a unique ecosystem in the Mexican desert.

Layered spherical growth structures similar to stromatolites, named "oncolites," are also known from the fossil record.

References

  • Grotzinger and Knoll; Stromatolites in Precambrian Carbonates: Evolutionary Mileposts or Environmental Dipsticks? 1999.
  • Allwood et al. (2006) Stromatolite reef from the early Archean era of Australia; Nature, 441 714-718.

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Lithification (from the Greek word lithos meaning 'rock' and the Latin-derived suffix -ific) is the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock.
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Sedimentary rock is one of the three main rock groups (the others being igneous and metamorphic rock). Rock formed from sediments covers 75-80% of the Earth's land area, and includes common types such as chalk, limestone, dolomite, sandstone, conglomerate and shale.
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microorganism (also spelled as microrganism) or microbe is an organism that is microscopic (too small to be seen by the human eye). The study of microorganisms is called microbiology.
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Cyanobacteria

Orders

The taxonomy is currently under revision.[1]

Cyanobacteria (Greek: κυανόs (kyanós) = blue + bacterium) also known as Cyanophyta
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phytoplankton — provide the food base for most marine food chains. In very high densities (so-called algal blooms) these algae may discolor the water and outcompete or poison other life forms.
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For other uses of the term, see Fossil (disambiguation)


FOSSIL is a standard for allowing serial communication for telecommunications programs under the DOS operating system.
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microorganism (also spelled as microrganism) or microbe is an organism that is microscopic (too small to be seen by the human eye). The study of microorganisms is called microbiology.
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Biota may refer to:
  • Biota (ecology)— the plant and animal life of a region
  • Biota (taxonomy)— a superdomain in taxonomy
  • Biota, Zaragoza— a municipality in Zaragoza province, Spain
  • Biota Holdings — an Australian biotech company

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In biology, abiotic components are non-living chemical and physical factors in the environment. These may be classified as light, temperature, water, atmospheric gases, and wind as well as soil and animal (edaphic) and physiographic (nature of land surface) factors.
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Oceanic crust      0-20 Ma
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Precambrian (Pre-Cambrian) is an informal name for the supereon comprising the eons of the geologic timescale that came before the current Phanerozoic eon. It spans from the formation of Earth around 4500 Ma (million years ago) to the evolution of abundant
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Archean (IPA: /ɑːˈkiːən/, also spelled Archaean, formerly called the Archaeozoic (IPA:
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For other uses of the term, see Fossil (disambiguation)


FOSSIL is a standard for allowing serial communication for telecommunications programs under the DOS operating system.
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''This is a biological article:
''For a territory administered by another territory see: Colony


''For a group attempting to affiliate with a Fraternity or Sorority see: Colony (fraternity)


In biology, a colony
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microorganism (also spelled as microrganism) or microbe is an organism that is microscopic (too small to be seen by the human eye). The study of microorganisms is called microbiology.
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Cyanobacteria

Orders

The taxonomy is currently under revision.[1]

Cyanobacteria (Greek: κυανόs (kyanós) = blue + bacterium) also known as Cyanophyta
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Proterozoic (IPA: /ˌprəʊt(ə)rəˈzəʊɪk/) is a geological eon representing a period before the first abundant complex life on Earth. The Proterozoic Eon extended from 2500 Ma to 542.
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Prehistory (Latin, præ = before Greek, ιστορία = history) is a term often used to describe the period before written history. Paul Tournal originally coined the term Pré-historique
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Chlorophyta
Reichenbach, 1834; Pascher[1][2]

Classes[3]
  • Bryopsidophyceae
  • Chlorophyceae
  • Pedinophyceae
  • Pleurastrophyceae
  • Prasinophyceae
  • Trebouxiophyceae
  • Ulvophyceae
Chlorophyta
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Green algae are microscopic protists; found in all aquatic environments, including marine, freshwater and brackish water.

The green algae (singular: green alga) are the large group of algae from which the embryophytes (higher plants) emerged.
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genus (plural: genera) is part of the Latinized name for an organism. It is a name which reflects the classification of the organism by grouping it with other closely similar organisms.
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The geological time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of Earth.
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Collenia is a genus of cyanobacteria that may form stromatolites.
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In astronomy, geology, and paleontology, bya or "b.y.a." is an acronym for billion years ago. This abbreviation is commonly used as a unit of time to denote length of time before the present. Specifically, one bya is equal to 109 years ago.
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Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state.
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2, −1
(neutral oxide)
Electronegativity 3.44 (Pauling scale)
Ionization energies
(more) 1st: 1313.9 kJmol−1
2nd: 3388.3 kJmol−1
3rd: 5300.5 kJmol−1

Atomic radius 60 pm
Atomic radius (calc.
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Multicellular organisms are organisms consisting of more than one cell, and having differentiated cells that perform specialized functions. Most life that can be seen with the naked eye is multicellular, as are all members of the kingdoms Plantae and Animalia (except for
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The Cambrian explosion describes the geologically sudden appearance of hard-bodied animals in the fossil record, around  million years ago. This is accompanied by a profound diversification of life[1] on Earth.
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