Stromatolites: When and How They Originated, Why They Are Important, Stromatolites in Mexico

The stromatolites they are microbial reefs formed by the activity of cyanobacteria (or blue-green algae), which are bacteria capable of photosynthesis. The word stromatolite is derived from Greek and means"stratified rock".

Stromatolite deposits are formed by the binding and trapping of marine sediments, as well as by mineral fixation activities of microbial communities. Live bacteria are found in the surface layer of a stromatolite.

Stromatolites

Instead, the underlying layers are the accumulation of marine sediments mixed with substances secreted by bacteria, and minerals. This pattern of growth generates a kind of fossil record. These deposits accumulate very slowly: a structure of 1 m can be from 2000 to 3000 years old.

However, the tiny microbes that make up modern stromatolites are similar to those that existed 3,500 million years ago. Stromatolites have been essential for the generation of the life of organisms that emerged later in evolutionary time, including human beings (species: Homo sapiens).

Index

  • 1 When and how did they originate?
  • 2 Why are they important?
    • 2.1 They are the main producers of oxygen on Earth
    • 2.2 They are the fossil evidence of the oldest organisms on the planet
    • 2.3 They are organisms that maintain their evolutionary line
    • 2.4 Participate in ancient biogeochemical cycles
  • 3 Stromatolites in Mexico
  • 4 Stromatolites in the rest of the world
  • 5 References

When and how did they originate?

The fossil record, created by the cyanobacteria in the stromatolites of Australia, suggests that they originated 3,500 million years ago. This is remarkable by itself, but even more if one takes into account that the oldest rocks that have been dated are 3,800 million years old.

These rock structures so distinctive of the stromatolites originated by several processes carried out by the cyanobacteria, among them photosynthesis. The photosynthetic mechanism is vital for the growth of cyanobacteria.

As the cyanobacteria grow, they consume the carbon dioxide that is present in the surrounding water. This causes a series of metabolic reactions that promote the formation of calcium carbonate, which precipitates and solidifies, thus forming"rocky"structures.

This process is favored because the cyanobacteria produce some sticky substances that help capture calcium carbonate and other minerals. These minerals form a crust over the cyanobacteria, which continue to grow around and through the crunchy layer.

When this process is repeated several times, one layer after another is formed, until the classic mushroom form of the stromatolite comes out of the water. Thus, the remains of these cyanobacteria have created the oldest fossils on Earth.

Why are they important?

Stromatolites are considered important for several reasons:

They are the main producers of oxygen on Earth

Before the cyanobacteria, the air had only 1% oxygen. Then, for 2000 million years, the photosynthetic stromatolites pumped the oxygen produced by photosynthesis to the oceans. They were a species of underwater trees, before there were terrestrial trees.

When the waters of the oceans were saturated oxygen was released in the air, and when the levels of this element rose to around 20% in the air, the life of many different organisms managed to flourish and evolve.

They are the fossil evidence of the oldest organisms on the planet

The mechanism by which stromatolites develop - their ability to leave layers (or strata) as they grow - results in a kind of rocky record.

This record can be observed at a glance in some cases, and in others with the help of a microscope. The solidification and maintenance of the layers for so many millions of years makes them evidence of the antiquity of the first life forms on Earth.

They are organisms that maintain their evolutionary line

The success in the reproduction and development of stromatolites has allowed these organisms to have survived the changing conditions of the Earth for billions of years.

This efficiency in the adaptive mechanisms that have allowed them to survive since they originated, some 3500 million years ago, gives them the property of maintaining their evolutionary lineage since their appearance.

Participate in ancient biogeochemical cycles

Because the microorganisms that form the stromatolites recycle the elements in the natural environment, they absorb and produce molecules that are part of the biogeochemical cycles.

The carbon cycle is very important in atmospheric processes, as well as the levels of carbon dioxide (CO) 2 ), and the formation of certain carbonates and biomolecules. It also participates in climate processes, such as the greenhouse effect.

Carbon atoms are constantly being recycled on the planet. Frequently carbon enters the cycle by fixing it in salt molecules, such as calcium carbonate (CaCO) 3 ). This is the main compound precipitated by the cyanobacteria of stromatolites.

Stromatolites in Mexico

Stromatolites grow only in certain parts of the world. In Mexico they are only found in the Cuatrociénagas reserve in Coahuila and in the lagoon of the seven colors in Bacalar.

In the Bacalar lagoon the stromatolites are the main tourist attraction and are distributed along seven kilometers, in a town known as Los Rápidos.

Specialists from the Autonomous University of Mexico presented a study to the authorities where the deterioration suffered by stromatolites in the Laguna de los siete colores is exposed.

The above represents a damage to the environmental health of the lagoon, because stromatolites fulfill the role of reefs and because they are the main producers of oxygen in the region.

In some areas of the lagoon the damage is already reflected. This promoted the creation of a committee among the municipal governments involved, where a series of agreements was reached in order to preserve these organisms because of their great importance as the first evidence of life on Earth.

Stromatolites in the rest of the world

Apart from Mexico, there are very few places where you can find these stromatolites, as in The Shark Bay in Australia, Andros Island in the Bahamas and the Persian Gulf, where the oldest formations are found.

Stromatolites can also be seen in the Red Sea on the western coast of Australia, in Lake Salgada in Rio de Janeiro, in the salt flats of northern Chile, and in San Juan de Marcona in Peru.

References

  1. Allwood, A.C., Grotzinger, J.P., Knoll, A.H., Burch, I.W., Anderson, M.S., Coleman, M.L., & Kanik, I. (2009). Controls on development and diversity of Early Archean stromatolites. Proceedings of the National Academy of Sciences of the United States of America , 106 (24), 9548-55.
  2. Awramik, S. (1992) The History and Significance of Stromatolites. In: Schidlowski M., Golubic S., Kimberley M.M., McKirdy D.M., Trudinger P.A. (eds) Early Organic Evolution. Springer, Berlin, Heidelberg.
  3. Grotzinger, J. P., & Rothman, D. H. (1996). An abiotic model for stromatolite morphogenesis. Nature .
  4. Lepot, K., Benzerara, K., Brown, G. E., & Philippot, P. (2008). Microbially influenced formation of 2,724-million-year-old stromatolites. Nature Geoscience , 1 (2), 118-121.
  5. Nutman, A. P., Bennett, V. C., Friend, C. R. L., Van Kranendonk, M. J., & Chivas, A. R. (2016). Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures. Nature , 537 (7621), 535-538.
  6. Riding, R. (2007). The term stromatolite: towards an essential definition. Lethaia , 32 (4), 321-330.


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