541 million year old clues suggest sea sponges were the first creatures on Earth

Marine sponges were likely the first living organisms on Earth and are consequently our oldest ancestors, suggests a new study published in the Proceedings of the National Academy of Sciences. The conclusion is based on an analysis of fossil chemical compounds in rocks more than 541 million years old, which is a fascinating development following the highly publicized discoveries made in Oman in the early 2000s.

“At the intersection of pharmacognosy and geochemistry, we have identified traces of biomolecules that have remained buried since before the Cambrian explosion when complex multicellular life with scales and skeletons emerged. The remnants show distinct similarities to substances that modern day demosponges emit and add new weight to the hypothesis that sea sponges were the first living organisms, which in turn can provide further natural history insights,” says Paco Cardenas, Pharmacognost at Uppsala University and co-author of the article.

The chemical fossils at the core of the study are a specific form of steranes – the geologically stable form of sterols that are found in the cell membranes of complex organisms. The steranes in question led the researchers to the marine demosponges that today occur in a variety of aquatic environments, live attached to rocks and corals and play a central role in the marine food chain as food for various animals.

"Today, demosponges come in a huge variety of sizes and colors, and live throughout the oceans as soft and squishy filter feeders, which means they feed on small particles in the water. "We don’t know exactly what these organisms would have looked like back then, but they absolutely would have lived in the ocean, been soft-bodied, and most likely did not have a silica skeleton,” says Roger Summons, Professor of Geobiology Emeritus at the Massachusetts Institute of Technology and last author of the article.

For thousands of years, nature has been our main source of pharmaceutical drugs. Unfortunately, science has yet only managed to map a few percent of all known organisms, and with exploitation and climate change threatening to eliminate countless species, many scientists are turning their focus to the deep sea, whose biodiversity still offers potential gold mines for new chemistry.

“Studies show that marine environments can have greater biological diversity than rainforests, and sea sponges in particular offer a wealth of unexplored opportunities. Today, we see how coral reefs are dying from rising water temperatures, and it is reasonable to assume that sponge reefs are affected in a corresponding way - so my hope is that every scientific success contributes to both increased research grants and greater awareness of the extremely important ecosystems that are at risk of vanishing,” states Paco Cardenas.

text: Magnus Alsne, photo: Mikael Wallerstedt, Nick Hobgood a o