When picturing the earliest animals on Earth, most people imagine ancient fish or tiny marine creatures drifting through prehistoric seas. But new research has revealed a far more humble origin story – one that begins with a sea sponge. According to a study published in Proceedings of the National Academy of Sciences, a 541-million-year-old sponge is now confirmed as one of the planet’s first animals.
This article is for general informational purposes only. Scientific understanding may evolve as further research emerges. Photos are for illustrative purposes only.
Traces Of The Earliest Animal Life
Scientists reached this conclusion after analyzing “chemical fossils” – molecular traces left behind by once-living organisms. These ancient clues, preserved in rocks, act as time capsules from a world before bones or shells existed. The evidence points to a class of sponges known as demosponges, a group that still lives in today’s oceans and shares genetic similarities with its prehistoric ancestors.
Roger Summons, a professor at MIT’s Department of Earth, Atmospheric and Planetary Sciences, explained that these creatures were soft-bodied and ocean-dwelling, likely lacking the silica skeletons seen in some modern species. Though their exact form remains unknown, their chemical signature has survived hundreds of millions of years beneath the sea floor.
What Are Chemical Fossils?
Chemical fossils, also called molecular fossils, are biomolecules that once belonged to living organisms but became buried and chemically transformed over time. In this study, scientists identified compounds called steranes, which are the stable geological forms of sterols – molecules similar to cholesterol.
Sea sponges produce two specific types of steranes: 30-carbon and 31-carbon. The researchers found an abundance of the rarer 31-carbon steranes in rock samples from Oman, western India, and Siberia. These findings suggest that sponge-like organisms were already thriving over 541 million years ago, during the Ediacaran Period, long before the rise of most other animal life.
“These special steranes were there all along. It took asking the right questions to seek them out and to really understand their meaning,” explained Lubna Shawar, a research scientist at Caltech.
Strengthening The Case For Sea Sponges
This isn’t the first time sponges have been linked to the origins of animal life. Back in 2009, researchers found evidence of 30-carbon sterols in rocks from Oman – the same type produced by modern sea sponges. At the time, the discovery hinted that sponges might have been among the earliest multicellular animals, but some scientists questioned whether the compounds could have come from other sources, such as bacteria or geological processes.
The new detection of 31-carbon sterols, however, adds a compelling layer of proof. Researchers believe this molecule is unique to sea sponges, ancient and modern alike, confirming that its presence is biological rather than geological.
“It’s a combination of what’s in the rock, what’s in the sponge, and what you can make in a chemistry laboratory,” said Summons. “You’ve got three supportive, mutually agreeing lines of evidence, pointing to these sponges being among the earliest animals on Earth.”
A Window Into Earth’s Earliest Ecosystems
The study reshapes our understanding of how animal life began. Long before the first fish swam or dinosaurs roamed, these simple organisms were filtering seawater, forming the foundation of early marine ecosystems.
Future research will focus on identifying similar sterols in rocks from other regions around the world. By expanding the sample base, scientists hope to pinpoint when and where the first animals emerged, tracing the delicate chemical footprints that began the story of life as we know it.
