For centuries, scientists studying evolution have debated one fundamental mystery: what did the very first animal on Earth look like? Genetic evidence has long divided experts. Some believe modern sponges (demosponges, Porifera) are the closest living relatives of our earliest ancestor, while others argue that comb jellies were the first to emerge in the primordial oceans. Now, a groundbreaking study from the Massachusetts Institute of Technology (MIT) adds powerful evidence supporting the “team sponge” theory. Researchers uncovered chemical traces that indicate sponges existed during the Neoproterozoic Era, over 541 million years ago, long before complex life diversified. Because the fossil record is incomplete—especially for soft-bodied organisms such as sponges and comb jellies—scientists have relied on alternative clues. These animals lacked bones or shells, leaving few traditional fossils behind. Sponges occasionally leave biomineralized spicules of calcium carbonate or silica, but studies suggest the earliest forms had none. Meanwhile, the comb jelly hypothesis rests mostly on DNA data, not fossils. To resolve this, scientists searched ancient Ediacaran sediments and oil deposits for chemical fingerprints unique to sponges. “We can’t know exactly what those first organisms looked like,” explains MIT geobiologist Roger Summons, “but they lived in the ocean, were soft-bodied, and likely lacked a silica skeleton.” Back in 2009, Summons and his colleagues found sponge-like sterols in 635-million-year-old rocks from Oman. These rare C30 sterols, fatty molecules in cell membranes, are characteristic of demosponges but absent in simpler life forms. “It’s extremely rare to find a sterol containing 30 carbons,” notes lead author Lubna Shawar, MIT organic geochemist. The finding suggests that early sponges might have been Earth’s first animals, predating other multicellular life. Some skeptics proposed that the Oman steranes could have originated from algae or non-biological processes. But Shawar’s team has now discovered another chemical fossil—a C31 sterol—produced by the same sponge gene responsible for the C30 compound. The same chemistry still occurs in living sponges today. “This study demonstrates how to verify a biomarker’s biological origin,” Shawar explains. “We confirmed the signal truly came from life, not contamination.” To test the idea, researchers recreated the fossilization process in the lab, synthesizing eight versions of C31 sterols under conditions mimicking hundreds of millions of years underground. Two of the samples precisely matched the ancient sterol remnants, confirming their biological—and sponge—origin. “It’s the alignment of what’s in the rock, in the sponge, and in the lab,” Summons says. “Together, these three lines of evidence point to sponges as some of the earliest animals on Earth.” “These unique steranes were always there,” Shawar adds. “It just took the right questions to find them and understand their true meaning.” With these ancient chemical signatures now confirmed, the MIT team plans to examine more geological samples worldwide to trace the earliest branches of animal life. The full research appears in PNAS (Proceedings of the National Academy of Sciences). What do you think about this discovery? Share your thoughts in the comments or spread the news on social media to help more people stay informed about the latest breakthroughs in technology, science, innovation, and gaming.

This research was published in PNAS.