Those are the words of recent groundbreaking news from geochemists at the Massachusetts Institute of Technology (MIT). In a major breakthrough for marine biologists, they found convincing signs that sea sponges were among the very first animals on Earth. This study suggests that these ancient organisms appeared significantly earlier than previously believed, potentially reshaping the timeline of multicellular life. Through the analysis of ancient rock samples, researchers found chemical fossils indicating that the ancestors of modern sea sponges roamed the oceans over half a billion years ago.
Firstly, the research was centered on sterols, a type of lipid crucial for cell membranes. Scientists analyzed rock samples from Oman, dating back to the Ediacaran Period, which lasted from approximately 635 million to 541 million years ago. The research revealed a distinct 30-carbon sterol that was likely a sterane. This unusual compound now seems strongly tied to ancient sea sponges, indicating they might have been one of the first animals on Earth.
Discovery of Chemical Fossils
The screen pointed to exciting evidence in the form of steranes. They went on to point out that these steranes were the preserved breakdown products of a 30-carbon sterol. This rare steroid, derived from ancient sea sponges, challenges previous conceptions about the timeline and complexity of early life forms.
Lubna Shawar, a lead co-author of the study and a consultant with World Resources Institute, noted that their findings are especially important because…
“These special steranes were there all along,” – Lubna Shawar
This claim adds further weight to the evidence already in support of these chemical signatures’ deep history found within ancient rock formations. The research further builds on the peer-research group’s previous work from 2009. Long ago, they found chemical fossils associated with the earliest known animals, sea sponges.
The role of sterols cannot be underestimated in terms of elucidating the biology of eukaryotic organisms. Roger Summons, the Schlumberger Professor of Geobiology Emeritus at MIT, described how sterols are critical in the evolution of cellular life.
“You’re not a eukaryote if you don’t have sterols or comparable membrane lipids,” – Roger Summons
This unexpected finding helps paint a picture of early animal life that’s richer and more complex than we’ve ever given them credit for. In making cellular structure and function, sterols were central players.
Analysis of Rock Samples
From this, the research team developed an integrated analysis approach to analyze rock samples from a field site—a large outcrop of rock in Oman. To their surprise, they found a rich source of steranes which they linked to an ancient lineage of marine sponges. This discovery is significant because finding a sterol with 30 carbon atoms is extremely uncommon.
“It’s very unusual to find a sterol with 30 carbons,” said Shawar, highlighting the uniqueness of their findings. The research team focused on the composition of modern-day sea sponges in order to understand their sterol preservation. It zeroed in on the more plentiful 31-carbon (C31) sterols.
To make sure the identification was accurate they developed a careful distinction between the ancient and modern form of sterols. The prominence of two specific C31 sterols is particularly noteworthy. Their coexistence, alongside the absence of others, is a dead giveaway that these compounds did not form through independent nonbiological processes by chance. This authenticity, in turn, is critical for verifying biological origins in geological samples.
“In this study we show how to authenticate a biomarker, verifying that a signal truly comes from life rather than contamination or non-biological chemistry,” – Lubna Shawar
This stringent approach goes a long way toward concretizing the link between these ancient chemical signatures and these early life forms.
Implications for Understanding Early Life
The potential impacts of this research go far beyond the discovery of these ancient organisms. The discovery helps illuminate an important period just prior to the Cambrian explosion. During this remarkable interval of geologic time, Earth’s biosphere fundamentally changed. Complex multicellular life exploded into existence.
The Ediacaran Period provides an interesting context to this evolutionary transition. In her new digital reconstruction, Summons brought to life what these primordial sea sponges would have looked like.
“We don’t know exactly what these organisms would have looked like back then, but they absolutely would have lived in the ocean, they would have been soft-bodied, and we presume they didn’t have a silica skeleton,” – Roger Summons
This description paints a picture of primitive life forms that contributed to shaping the marine ecosystems long before more complex organisms emerged.