Treasures Underfoot
This is an EarthCache, there is no physical container. To log it, you must go to the location indicated by the coordinates and answer the following questions:
1. Which organisms are responsible for the formation of stromatolites?
2. Standing near the coordinates, find stromatolites and describe them in your own words - their color, can you see layers, if so, are they uniform, how thick, if not, what is their structure, etc.
3. Look at the promenade you are walking on, what percentage of the pavement slabs are stromatolites:
A. All of it is made of stromatolites
B. More than 50%
C. Less than 50%
D. There are only individual slabs of stromatolites here.
4. Take a picture of yourself or your nickname on the coast of Ierapetra (no SPOILERS!)
The following text and observation of your surroundings may help you answer this question.
Walking along the seaside promenade of Ierapetra, in addition to gazing at the horizon, it is worth looking under your feet. Then you will realize that you are treading on true treasures of geology. In the vicinity of the coordinates, find one of the characteristic brown, richly laminated slabs and take a closer look at them.
We can begin our story in the Precambrian, some... 3.7 billion years ago! It was then that the first single-celled living organisms appeared, and right after them the first prokaryotic cyanobacteria. They are the only inhabitants of the Earth for the next 3.0 billion years! That's how long they needed to fill the atmosphere with oxygen in the process of photosynthesis and life could move on, creating the first multicellular organisms. You may ask: but how do we know this?! A rock was found in Australia that testifies to life processes, its age was determined to be 3.7 billion years. This rock is a stromatolite.
The Old Ones
Stromatolites are layered sedimentary rocks made of calcium carbonate, that are formed primarily by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly Proteobacteria). These microorganisms produce compounds that bind sand and other rock materials, creating mineral "microbial mats." These mats, in turn, build up layer by layer, gradually growing over time in shallow waters.
Layers of stromatolites
The formation of stromatolites is a complex process that takes thousands of years and can be described in several steps:
- Microbial growth: Stromatolites begin with the growth of microbial communities, mostly dominated by photosynthetic cyanobacteria.
- Microbial mat formation: These cyanobacteria, along with other microorganisms such as algae and photosynthetic bacteria, form thin layers on aquatic surfaces.
- Deposition: Sediment particles become trapped in the mats, contributing to the build-up of stromatolite structures.
- Biomineralization: Microbial activity by cyanobacteria causes the precipitation of minerals such as calcium carbonate within the stromatolite layers.
- Lamination: Microbial communities continue to trap sediment, forming laminated layers within the structure with alternating light and dark bands, depending on microbial activity and the environment.
The process of accreting successive layers creates the characteristic lamination of stromatolites. They occur in the form of layers, isolated or interconnected dome-shaped growth forms, and polygonal forms with cup-shaped bent laminations. Different styles of lamination of stromatolites have been described and can be studied using microscopic and mathematical methods. A stromatolite can grow to a meter or more. Fossilized stromatolites provide important records of some of the oldest forms of life. The oldest stromatolites discovered to date are 3.7 billion years old. They were found in the Isua Formation in Greenland. Slightly younger ones (220 million years old) occur in the Pilbara craton. Others, 3.4–3.5 billion years old, have been found in southern Africa (Sebakiwian Group) and Australia (Warrawoona Group). They are most common in sediments from 2.8–0.6 billion years ago, although examples from later epochs are known. The disappearance of this type of formation was gradual and most likely resulted from the activity of herbivores that prevented the development of cyanobacteria layers by scraping the algae from the surface. Nowadays, stromatolites are rare and occur only in special conditions of salinity or calcium carbonate saturation, where herbivores do not occur.
Stromatolites in Sharkbay By Paul Harrison, CC BY-SA 3.0
What's strangest is that in Ieraptera you can walk on precisely this type of rocks.
____________________________________________
Bibliography:
- "Przewodnik po petrografii" - pod red. A. Maneckiego, M. Muszyńskiego
- https://www.geological-digressions.com/
- Stromatolite - Wikipedia