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

Stromatolites provide the earliest geological evidence of life on Earth. These curious biotic structures are made of carpets of algae that grow toward the light and precipitate carbonates. After their first appearance 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 drastically changed the composition of our atmosphere with the introduction of oxygen. That oxygen initially destroyed competition from stromatolites, allowing their prominence in the Archean and early Proterozoic environment. However, as more life forms adapted their metabolism to an oxygen-rich atmosphere, stromatolites began to decline in number and only entered the geological record after mass extinctions or in harsh environments.

“The bacteria are always there, but usually don’t get the chance to make stromatolites,” explains Volker Vahrenkamp, ​​the author of a new study in Geology. “They are largely outcompeted by 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 Exuma Islands in the Bahamas were the only known modern analogue to the biologically diverse, open shallow marine environments where most Proterozoic stromatolites developed.

That is, until Vahrenkamp discovered living stromatolites on the island of Sheybarah, on the northeastern shelf of the Red Sea in Saudi Arabia. Vahrenkamp was studying teepee structures—salt crust domes visible from space—when he chanced upon the modest stromatolite field. The discovery was surprising, but fortunately Vahrenkamp is one of the few people who has previously seen stromatolites in the Bahamas.

“When I stepped on them, I knew what they were,” Vahrenkamp explains. “It’s 2,000 km of coastline of carbonate platforms, so in principle it’s a desirable area to look for stromatolites… but then again, in the Bahamas it’s the same, and yet there’s only one small area where you can find them.”

Sheybarah Island is an intertidal to shallow subtidal zone, with frequently alternating wetting and drying conditions, extreme temperature variations between 8°C and >48°C, and oligotrophic conditions, similar to the Bahamas. Since similar environmental conditions are widespread on the Al Wajh carbonate platform, there may be other stromatolite fields nearby. Vahrenkamp and his team have begun this exploration work, but stromatolites are small, about 6 inches in diameter, so they are difficult to spot until you get very close.

There are several hundred stromatolites in the field on Sheybarah Island. Some are well-developed, perfect textbooks. Others are more sheet-shaped, with low relief. “Maybe they are juvenile specimens,” Vahrenkamp hypothesizes, “but we don’t know what a baby stromatolite looks like.” They have to start small, but we don’t know that.’

Part of the problem is that we don’t know how fast stromatolites grow. Dating them is very difficult because they contain two different carbonate components that are virtually impossible to separate: the newly microbe-precipitated component, which is important, and the carbonate sand present in the environment, which is misleading. Currently, Vahrenkamp’s team monitors the field monthly to record any visual changes. An attempt could soon be made to transfer some stromatolites from Sheybarah Island to an aquarium and grow 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 early life and the evolution of Earth’s ocean and could even help us in the search for life on other planets such as Mars. What would life on Mars look like, and how would we recognize it? Looking at stromatolites, the first life forms on Earth, before our planet even had an oxygen-rich atmosphere, is a very promising approach.