New remains of the first life on Earth discovered in Saudi Arabia

Stromatolites constitute the first geological trace of life on Earth. These curious biotic structures are made up of mats of algae growing towards the light and precipitating carbonates. After first appearing 3.48 Ga ago, stromatolites dominated the planet as the only living carbonate factory for almost three billion years.

Stromatolites are also partly responsible for the Great Oxygenation Event, which radically changed the composition of our atmosphere by introducing oxygen. This oxygen initially eliminated competition from stromatolites, allowing their importance 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 harsh environments.

“The bacteria are still there, but they usually don’t have the opportunity to produce stromatolites,” says Volker Vahrenkamp, ​​author of a new study in Geology. “They are vastly outnumbered by the corals.”

In modern times, stromatolites are relegated to extreme niche 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 developed was the Exuma Islands in the Bahamas.

That is, until Vahrenkamp discovered living stromatolites on the island of Sheybarah, on the northeastern Red Sea shelf of Saudi Arabia. Vahrenkamp was studying tipi structures – salt-crusted domes visible 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 ever seen stromatolites in the Bahamas.

“When I stepped on it, I knew what it was,” Vahrenkamp says. “It’s 2,000 km of carbonate platform coastline, so in principle it’s a desirable area to look for stromatolites… but it’s the same thing in the Bahamas, and yet there’s only one small area where they are found.”

Sheybarah Island is a shallow intertidal to subtidal environment, with regular alternation of wet and drying conditions, extreme temperature variations between 8°C and >48°C and oligotrophic conditions, much like the Bahamas. Since similar environmental conditions are prevalent on the Al Wajh carbonate platform, there could be other stromatolite fields nearby. Vahrenkamp and his team began this exploration work, but stromatolites are small, about 15 cm in diameter, and therefore difficult to spot until you get very close.

There are several hundred stromatolites in the Sheybarah Island field. Some are well-developed and perfect textbook examples. Others are more leaf-shaped, 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 that.”

Part of the problem is that we don’t know how quickly stromatolites grow. Dating them is very difficult, because they contain two different carbonate components that are virtually impossible to separate: the one newly precipitated by microbes, which is interesting, and the carbonate sand present in the environment, which is misleading. Currently, Vahrenkamp’s team monitors the terrain monthly to record any visual changes. Soon, an attempt could be made to transfer some of the stromatolites from Sheybarah Island to an aquarium and cultivate them there – an exciting experimental prospect.

Vahrenkamp’s discovery offers us the opportunity to better understand the formation and growth of stromatolites. This will provide insight into the beginnings of life and the evolution of oceans on Earth and could even help us in the search for life on other planets like Mars. What would life be like on Mars and how would we recognize it? Focusing on stromatolites, which were the first forms of life on Earth, even before our planet had an oxygenated atmosphere, is a very promising avenue.