Our planet is home to diverse geological formations and structures that can truly surprise us. One of these is the stromatolite . These are layered or stratified rock structures formed from sediments and/or minerals deposited over time by communities of both green and blue-green algae. Stromatolites can be found in both freshwater and saltwater, as well as in evaporite deposits.
In this article we are going to tell you what the characteristics are, where they are found and what is the importance of stromatolites.
What are stromatolites
Stromatolites are layered or stratified rock structures formed from sediments and/or minerals deposited by communities of blue-green algae. They can be found in freshwater or saltwater bodies and evaporative sediments in various locations around the world. Blue-green algae, more commonly known today as cyanobacteria, represent a group of aquatic prokaryotes—belonging to the kingdom of bacteria—that can obtain energy from sunlight; that is, they can perform photosynthesis.
Cyanobacteria are one of the most important and abundant groups of prokaryotic organisms. Like all bacteria, they are microscopic, single-celled organisms, although they often grow into colonies large enough to be seen with the naked eye. These photosynthetic microorganisms may be among the first living organisms on Earth, as the oldest fossils found date back more than 3.000 billion years and are cyanobacteria found in stromatolites.
Stromatolites are structures formed by the metabolic activities of microbial communities, dominated by cyanobacteria, which can precipitate and deposit a large amount of sediments and minerals, mainly limestone. These rock structures are considered the oldest ecosystems on our planet, and Shark Bay in Western Australia is home to the oldest specimens.
The importance of stromatolites lies in their microbial composition, because the cyanobacteria they contain produce large quantities of oxygen needed by animals and other organisms in the biosphere. Furthermore, stromatolites provide us with information about Earth's stratigraphy throughout history.
Key features
Let's see what are the main characteristics that stromatolites have for which they can stand out:
- They are rocky structures formed by microorganisms, mainly cyanobacteria, are also called organic sedimentary structures because they are derived from the metabolic activities of the microorganisms that compose them.
- They can exhibit other organisms, such as single-celled algae, fungi, insects, crustaceans, etc., depending on where they are found.
- Its rocky composition is formed by a mixture of limestone and dolomite (they are rich in calcium carbonate).
- They form in the direction of sunlight like plants, so they "grow" vertically and are arranged in sheets or layers, layer by layer.
- The outermost layer is the youngest and the longest is the base.
- They grow or settle very slowly, so they almost always have a structure that is hundreds or thousands of years old.
- They live in shallow or shallow waters, grow on the ground, and are highly sensitive to climate change, changes in sea level, and pollution.
- They can reach a height of about 50 cm from the ground, and are rectangular, column-shaped, dome-shaped, spherical, nodular, or completely irregular.
- There are very old complete fossils.
Importance of stromatolites
Stromatolites usually exist in the aquatic environment of the ocean or in fresh water, and they usually form in shallow waters. The western tip of Australia is one of the most famous places where "modern" stromatolites exist in high salt lakes.
Stromatolites have been and continue to be vital for life on Earth's surface. Since the cyanobacteria they contain are among the oldest known organisms, their photosynthetic activities are thought to have contributed to the formation of the oxygen-rich atmosphere we live in today and ultimately led to the development of aerobic organisms.
Furthermore, as we have already mentioned, these structures still contribute a significant amount of oxygen to our atmosphere, making life dependent on them. Despite their relatively simple structure, stromatolites are considered very important in the fields of biology, geology, and even astronomy, primarily because their study yields valuable information. For example, in geology, stromatolites provide valuable data for subdisciplines such as stratigraphy, sedimentology, paleogeography, paleontology, and geophysics.
However, in general, its importance lies in the following functions:
- Explain the ancestral conditions of some environments, especially regarding the amount of salt and the deposition of different compounds.
- Identify places where there was biological activity in the past.
- Determine the age of some ecosystems.
- Draw the previous shoreline.
- Limit the time of origin of photosynthetic organisms (like algae) and the formation of biological communities.
- Understand the rate of accumulation of sediment in certain places.
- Learn what microfossils look like.
Places in the world where we can find them
As we have mentioned before, there are numerous places in the world where we can find stromatolites. However, we are going to highlight some fixed places where we know we can find:
- The Pampa del Tamarugal National Reserve, in Tarapacá, Tamarugal province, Chile.
- The Cuatrociénegas Basin, in the white desert of Coahuila and Lake Alchichica, Mexico.
- The Bacalar lagoon, in the Yucatan Peninsula, south of Mexico.
- The Laguna Salada, in the state of Rio Grande do Norte, Brazil.
- Lake Salda, in Turkey.
- The Exuma Cays, Exuma District, Bahamas Islands.
- Pavillion Lake, British Columbia, Canada.
- Blue Lake, southeast Australia.
Stromatolites are not a common structure in all aquatic ecosystems on our planet , but they are generally distributed in a limited environment where conditions favor the deposition of the minerals that compose them.
In Mexico, only 4 sites are known that describe "recently" formed stromatolites:
- Cuatrocienegas Basin: Located in the Cuatrociénegas Valley Reserve near the Coahuila Desert in the State of Coahuila de Zaragoza in the northern part of the country.
- Lake Alchchica: A salty lake with a high concentration of magnesium in the sovereign free state of Puebla, near the center of the country.
- Laguna de Bacalar, also known as the Laguna de los Siete Colores de Bacalar: Located in the Yucatan Peninsula, it belongs to the state of Quintana Roo.
- Chichankanab Lagoon: it also belongs to the state of Quintana Roo.
I hope that with this information you can learn more about stromatolites and their characteristics.