Sea Sponges Were Likely The First Animals On Earth

In a new study, scientists have strengthened the case for the sea sponges as Earth’s first animals with the genetic analysis of a molecule present in a 640-million-year old rock by the Massachusetts Institute of Technology (MIT).

Long held belief about sea sponges made stronger by researchers

Many scientists have longed believed that the sea sponges were the first animals on Earth and this paper published in the journal Proceedings of the National Academy of Sciences by lead author David Gold and senior author Roger Summons, nearly confirms it. Both researchers are from MIT.

By confirming that the molecule belongs to a sponge buts it back 640 million years which is quite a bit of time before that Cambrian Explosion which occurred 540 million years ago. It was during the Cambrian Explosion that single-cell creatures gave way to all sorts of different animal groups in a relatively short period of time geologically speaking at least.

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Scientists estimate that there are somewhere between 5,000 and 10,000 sponges in the sea, each belonging to the phylum Porifera (which means “pore bearer”). Sponges require a steady flow of water through their bodies for food, oxygen and to expel waste owing to their lack of a nervous, digestive or circulatory system.

The Cambrian Explosion provided scientists with no shortage of fossils to be examined and countless findings have come from these over the year and will continue to bring new understandings of early life to scientists and laymen alike. However, pre-Cambrian fossils are another story with very few of them in existence and readily available for scientific study.

Rocks rather than fossils

This lack of pre-Cambrian fossils is the reason that the pair turned their research to rocks looking for molecular fossils. Molecular fossils can be found in rocks, and are effectively pieces left by the creature when it decayed long ago.

The pair from MIT focused on a very specific molecule known as 24-isopropylcholestane, or 24-ipc. Research by others in the past had found it present in rocks of the same age. While sponges produce 24-isopropylcholestane, they are not alone as certain types of algae do as well. So the presence of 24-isopropylcholestanem by itself was not enough, the two had to prove that it came from the sponge.

In order to do this, the researchers identified the gene responsible for the production of 24-isopropylcholestane. That still wasn’t enough as both the sponge and algae have the extra gene. But, by tracing back they realized that the sponge developed this gene quite a bit before algae meaning that the 24-isopropylcholestane found in the rock was indeed from a sponge..

“We brought together paleontological and genetic evidence to make a pretty strong case that this really is a molecular fossil of sponges,” said Gold in a statement. “This is some of the oldest evidence for animal life.”

“This brings up all these new questions,” Gold added. “What did these organisms look like? What was the environment like? And why is there this big gap in the fossil record? This goes to show how much we still don’t know about early animal life, how many discoveries there are left, and how useful, when done properly, these molecular fossils can be to help fill in those gaps.”

At least for now, the sea sponge will continue to have a hold on the title, Earth’s first living creature.