Some of the first animals on Earth were likely ancestors of the modern sea sponge, according to MIT geochemists who unearthed new evidence in very old rocks.
Image: Jose-Luis Olivares, MIT
The first animals on Earth may have been sea sponges, study suggests | MIT News | Massachusetts Institute of Technology
Another fatal blow against creationism was revealed recently by geochemists led by Professor Roger E. Summons of the Massachusetts Institute of Technology (MIT), with news that they have found chemical evidence in ancient rocks suggesting that the earliest animals may have been the ancestors of sponges, living some 541 million years ago. Their findings have just been published in Proceedings of the National Academy of Sciences of the USA.
They succeeded in extracting the chemical signature of animal life from rocks in Oman, where they found an abundance of steranes that they determined were the preserved remnants of 30-carbon (C30) sterols — a rare form of steroid that they showed was most likely derived from ancient sea sponges known as demosponges.
Not only is this fatal to creationists' notion of Earth being just a few thousand years old, with all living organisms magically created without ancestry and with different “kinds” unrelated to other “kinds”, but it also delivers another hammer blow to the creationist parody of the so-called 'Cambrian Explosion' as a literal explosive creation of multiple body plans in a single event. Slightly more sophisticated creationists attempt to claim that this was the act of creation for which the tales in Genesis are merely a metaphor, with each day of 'creation week' representing millions of years — a claim that collapses on realisation that, according to Genesis, green plants would have had to exist for millions of years with no sun to drive photosynthesis, since the sun is supposedly created the 'day' after plants.
This analysis pushes the origins of the Cambrian biota back into the Ediacaran, showing not a sudden spontaneous creation 540 million years ago, but the cumulative products of evolutionary diversification, probably beginning with these early multicellular organisms.
In addition to Professor Roger E. Summons of MIT, the team included Dr Lubna Shawar of Caltech, Gordon Love of the University of California, Riverside, Benjamin Uveges of Cornell University, Alex Zumberge of GeoMark Research in Houston, Paco Cárdenas of Uppsala University in Sweden, and José-Luis Giner of the State University of New York College of Environmental Science and Forestry.
Molecular Fossils^ Chemical Traces of Ancient Life.Long before complete animal fossils appear in the geological record, life can sometimes be detected through its chemical fingerprints. These preserved molecules, known as biomarkers or molecular fossils, are distinctive compounds produced by living organisms that can survive in altered form within ancient sediments for hundreds of millions of years.
One important class of biomarkers is sterols — complex lipid molecules that form part of the cell membranes of many eukaryotes, including animals, algae, and fungi. When organisms die and are buried in sediments, these sterols gradually transform through chemical processes during burial and heating. Over geological time they are converted into more stable molecules called steranes, which can persist in sedimentary rocks and petroleum deposits.
Because different groups of organisms produce distinctive sterols, the steranes derived from them can act as chemical signatures identifying the types of life present when the sediments were deposited. In effect, they function as a kind of chemical fossil record, revealing biological communities even when no visible fossils are preserved.
In the case of the Omani rocks analysed by the MIT-led team, researchers detected an abundance of C₃₀ steranes. These molecules are particularly significant because they are rare in most organisms but are characteristic of certain demosponges, a major group of marine sponges. Their presence therefore strongly suggests that sponge-like animals were already living in the oceans at the time these sediments formed.
Such molecular evidence allows scientists to trace the origins of animal life further back than the traditional fossil record alone permits. While visible sponge fossils are rare in very ancient rocks, their chemical signatures can persist for hundreds of millions of years, providing crucial clues about the early evolution of animals and the ecosystems of the late Precambrian oceans.
Details of the team's research are given in an MIT news release by Jennifer Chu.
The first animals on Earth may have been sea sponges, study suggests
MIT researchers traced chemical fossils in ancient rocks to the ancestors of modern-day demosponges.
A team of MIT geochemists has unearthed new evidence in very old rocks suggesting that some of the first animals on Earth were likely ancestors of the modern sea sponge.
In a study appearing today in the Proceedings of the National Academy of Sciences, the researchers report that they have identified “chemical fossils” that may have been left by ancient sponges in rocks that are more than 541 million years old. A chemical fossil is a remnant of a biomolecule that originated from a living organism that has since been buried, transformed, and preserved in sediment, sometimes for hundreds of millions of years.
The newly identified chemical fossils are special types of steranes, which are the geologically stable form of sterols, such as cholesterol, that are found in the cell membranes of complex organisms. The researchers traced these special steranes to a class of sea sponges known as demosponges. Today, demosponges come in a huge variety of sizes and colors, and live throughout the oceans as soft and squishy filter feeders. Their ancient counterparts may have shared similar characteristics.
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.
Professor Roger E. Summons,
Department of Earth, Atmospheric and Planetary Sciences (EAPS) Massachusetts Institute of Technology.
Cambridge, MA, USA.
The group’s discovery of sponge-specific chemical fossils offers strong evidence that the ancestors of demosponges were among the first animals to evolve, and that they likely did so much earlier than the rest of Earth’s major animal groups.
The study’s authors, including Summons, are lead author and former MIT EAPS Crosby Postdoctoral Fellow Lubna Shawar, who is now a research scientist at Caltech, along with Gordon Love from the University of California at Riverside, Benjamin Uveges of Cornell University, Alex Zumberge of GeoMark Research in Houston, Paco Cárdenas of Uppsala University in Sweden, and José-Luis Giner of the State University of New York College of Environmental Science and Forestry.
Sponges on steroids
The new study builds on findings that the group first reported in 2009. In that study, the team identified the first chemical fossils that appeared to derive from ancient sponges. They analyzed rock samples from an outcrop in Oman and found a surprising abundance of steranes that they determined were the preserved remnants of 30-carbon (C30) sterols — a rare form of steroid that they showed was likely derived from ancient sea sponges.
The steranes were found in rocks that were very old and formed during the Ediacaran Period — which spans from roughly 541 million to about 635 million years ago. This period took place just before the Cambrian, when the Earth experienced a sudden and global explosion of complex multicellular life. The team’s discovery suggested that ancient sponges appeared much earlier than most multicellular life, and were possibly one of Earth’s first animals.
However, soon after these findings were released, alternative hypotheses swirled to explain the C30 steranes’ origins, including that the chemicals could have been generated by other groups of organisms or by nonliving geological processes.
The team says the new study reinforces their earlier hypothesis that ancient sponges left behind this special chemical record, as they have identified a new chemical fossil in the same Precambrian rocks that is almost certainly biological in origin.
Building evidence
Just as in their previous work, the researchers looked for chemical fossils in rocks that date back to the Ediacaran Period. They acquired samples from drill cores and outcrops in Oman, western India, and Siberia, and analyzed the rocks for signatures of steranes, the geologically stable form of sterols found in all eukaryotes (plants, animals, and any organism with a nucleus and membrane-bound organelles).
You’re not a eukaryote if you don’t have sterols or comparable membrane lipids.
Professor Roger E. Summons.
A sterol’s core structure consists of four fused carbon rings. Additional carbon side chain and chemical add-ons can attach to and extend a sterol’s structure, depending on what an organism’s particular genes can produce. In humans, for instance, the sterol cholesterol contains 27 carbon atoms, while the sterols in plants generally have 29 carbon atoms.
It’s very unusual to find a sterol with 30 carbons
Lubna Shawar, first author
Department of Earth, Atmospheric and Planetary Sciences
Massachusetts Institute of Technology
Cambridge, MA, USA.
The chemical fossil the researchers identified in 2009 was a 30-carbon sterol. What’s more, the team determined that the compound could be synthesized because of the presence of a distinctive enzyme which is encoded by a gene that is common to demosponges.
In their new study, the team focused on the chemistry of these compounds and realized the same sponge-derived gene could produce an even rarer sterol, with 31 carbon atoms (C31). When they analyzed their rock samples for C31 steranes, they found it in surprising abundance, along with the aforementioned C30 steranes.
These special steranes were there all along. It took asking the right questions to seek them out and to really understand their meaning and from where they come.
Lubna Shawar.
The researchers also obtained samples of modern-day demosponges and analyzed them for C31 sterols. They found that, indeed, the sterols — biological precursors of the C31 steranes found in rocks — are present in some species of contemporary demosponges. Going a step further, they chemically synthesized eight different C31 sterols in the lab as reference standards to verify their chemical structures. Then, they processed the molecules in ways that simulate how the sterols would change when deposited, buried, and pressurized over hundreds of millions of years. They found that the products of only two such sterols were an exact match with the form of C31 sterols that they found in ancient rock samples. The presence of two and the absence of the other six demonstrates that these compounds were not produced by a random nonbiological process.
The findings, reinforced by multiple lines of inquiry, strongly support the idea that the steranes that were found in ancient rocks were indeed produced by living organisms, rather than through geological processes. What’s more, those organisms were likely the ancestors of demosponges, which to this day have retained the ability to produce the same series of compounds.
It’s a combination of what’s in the rock, what’s in the sponge, and what you can make in a chemistry laboratory. You’ve got three supportive, mutually agreeing lines of evidence, pointing to these sponges being among the earliest animals on Earth.
Professor Roger E. Summons.
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.
Now that the team has shown C30 and C31 sterols are reliable signals of ancient sponges, they plan to look for the chemical fossils in ancient rocks from other regions of the world. They can only tell from the rocks they’ve sampled so far that the sediments, and the sponges, formed some time during the Ediacaran Period. With more samples, they will have a chance to narrow in on when some of the first animals took form.
Publication:
The significance of this discovery extends far beyond a technical discussion of molecular fossils. It provides yet another line of independent evidence that the early history of animal life stretches deep into the Precambrian, long before the period when complex fossils become common in the Cambrian rocks. What once appeared to be a sudden “explosion” of animal life is increasingly understood as the point at which evolving organisms acquired hard parts and body structures that fossilise readily. The evolutionary diversification itself had already been underway for tens of millions of years.
By revealing the chemical traces of sponge-like animals living in Ediacaran seas more than half a billion years ago, this research helps fill in another piece of the puzzle of early animal evolution. It shows that the Cambrian fauna did not appear out of nowhere, but emerged from earlier, simpler multicellular organisms whose presence is recorded not only in rare fossils but also in the molecular fingerprints preserved within ancient rocks.
Once again, the picture that emerges from modern science is one of deep time, gradual evolutionary innovation, and a long prehistory of life preceding the more familiar fossil record. Each new discovery like this pushes the origins of animal life further back and adds detail to the evolutionary story — while leaving creationist claims of sudden supernatural creation looking increasingly disconnected from the accumulating evidence.
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