What are stromatolites?
Stromatolites areby definition, laminated organo-sedimentary structures (typically CaCO3) that grow attached to the substrate and emerge vertically from it, producing structures of great morphological, volumetric and biogeographic variety.
Stromatolites are also partially responsible for the Great Oxygenation Event, which dramatically changed the composition of our atmosphere by introducing oxygen. That oxygen initially eliminated competition from stromatolites, allowing their prominence in the Archean and early Proterozoic environment. However, as more life forms adapted their metabolism to an oxygenated atmosphere, stromatolites began to decline, appearing in the geological record only after mass extinctions or in difficult environments.
The diversification of life on Earth could have been due to a weak magnetic field millions of years ago
Stromatolites: living in extreme situations
“Bacteria are always present, but usually do not have the opportunity to produce stromatolites“, Explain Volker Vahrenkampauthor of a new study in Geologistand.
In modern times, Stromatolites are relegated to extreme environments, such as hypersaline marine environments (e.g., Shark Bay, Australia) and alkaline lakes. Until recently, the only known modern analogue of the biologically diverse, open, shallow marine environments where most Proterozoic stromatolites They were the Exuma Islands in the Bahamas.
That is, until Vahrenkamp discovered living stromatolites on Sheybarah Island, on the northeastern shelf of the Red Sea in Saudi Arabia. Vahrenkamp was studying tipi structures (salt crust domes that can be seen from space) when he came across the modest stromatolite field. The discovery was surprising, but fortunately, Vahrenkamp is one of the few people who has seen stromatolites before in the Bahamas.
“When I stepped on them, I knew what it wasn,” explains Vahrenkamp. “There are 2,000 kilometers of carbonate shelf coast, so in principle it is a desirable area to look for stromatolites… but it is the same in the Bahamas, and yet there is only a small area where they can be found“.
Sheybarah Island It is a shallow intertidal and subtidal environment, with regularly alternating wet and dry conditions, oscillations temperature extremes between 8 °C and >48 °C and oligotrophic conditions, very similar to the Bahamas. Since similar environmental conditions are widespread throughout the Al Wajh carbonate platform, there could be other stromatolite fields nearby. Vahrenkamp and his team have begun this exploration work, but the stromatolites are small, about 15 cm in diameter, and therefore difficult to detect until one gets very close.
There are several hundred stromatolites in the Sheybarah Island field. Some are examples of perfect, well-developed textbooks. Others are more laminar, with low relief. “Maybe they could be juveniles“Vahrenkamp hypothesizes, “but we don’t know what a baby stromatolite looks like. They must start small, but we don’t know“.
As far as we know, the discovery of Sheybarah stromatolite is the first of its kind in the Middle East, which presents an unprecedented opportunity to study its geobiology in this unique geographic region. Modern open shallow marine stromatolites are sparsely present on the planet, leading to a lack of suitable analogues for their ancient counterparts.
The ages on Earth
The age of the Earth as an accreted planet it is calculated in 4500 million years. The oldest igneous rocks on Earth are in Greenland and are 3.8 billion years old.
The oldest stromatolites They are from Warrawoona, Australia and They are about 3500 million years old (Precambrians – Archaeans). The theory says that, given the conditions at that time, the first inhabitants of the Earth must have been single-celled, prokaryotic, and anaerobic organisms. Stromatolites are therefore part of the most important fossil record of early microbiological life. The recent study may put the emergence of life on Earth beyond 3.5 billion years.
Life on Mars from stromatolites?
Vahrenkamp’s discovery gives us the opportunity to better understand the formation and growth of stromatolites. This will provide information about early life and the evolution of oceans on Earth and may even help us in the search for life on other planets such as Mars.
What would life be like on Mars and how would we recognize it? Observing stromatolites, which were the first forms of life on Earth, before our planet even had an oxygenated atmosphere, is a very promising avenue.
Reference
Volker Vahrenkamp et al, Discovery of modern living intertidal stromatolites on Sheybarah Island, Red Sea, Saudi Arabia, Geology (2024). DOI: 10.1130/G51793.1
This entry was published in News on 03 Jun 2024 by Francisco Martín León
