Sea Sponge Challenges Theory On The Origin Of Animals
February 18, 2014

Study Suggests High Oxygen Levels Not Required For Complex Life

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redOrbit Staff & Wire Reports - Your Universe Online

In sharp contrast to the longstanding belief among scientists that advanced life on Earth was only able to evolve once atmospheric oxygen levels rose to near-modern levels, new research has discovered a small sea sponge which they claim proves that a high concentration is not needed in order for complex creatures to live and grow.

According to the authors of the new study, which appears in Monday’s edition of the journal Proceedings of the National Academy of Sciences (PNAS), complex life first evolved when atmospheric levels of oxygen began to increase approximately 630 to 635 million years ago.

However, a sea sponge that was fished out of Kerteminde Fjord in Denmark is challenging that theory, as the creature demonstrates that animals are able to grow and thrive with extremely limited oxygen supplies. In fact, they can stay alive when the atmosphere contains just 0.5 percent of the oxygen content of typical modern levels.

“Our studies suggest that the origin of animals was not prevented by low oxygen levels,” and Daniel Mills of the Nordic Center for Earth Evolution at the University of Southern Denmark, who co-wrote the PNAS paper alongside Lewis M. Ward from the Caltech Division of Geological and Planetary Sciences.

Animals and other advanced forms of life first evolved approximately half a billion years ago, and billions of years before that, life consisted solely of single-celled beings. Since complex life emerged alongside the significant increase in atmospheric oxygen, experts believed that the two events were clearly linked in a causal manner – that the increased amounts of oxygen present in the air gave rise to the evolution of animals.

”But nobody has ever tested how much oxygen animals need – at least not to my knowledge. Therefore we decided to find out,” Mills explained. “When we placed the sponges in our lab, they continued to breathe and grow even when the oxygen levels reached 0.5 per cent of present day atmospheric levels.”

The sponges in question, a species known as Halichondria panicea, are among the living animals that most closely resemble the first animals to have lived on the ancient Earth. Furthermore, the creatures live in close proximity to the University of Southern Denmark's Marine Biological Research Centre in Kerteminde.

As for the oxygen levels these sponges require in order to survive, Mills and Ward report that they are lower than the amount scientists believed was a prerequisite for animal life. But if it wasn’t low oxygen levels that kept creatures from evolving, what was it and why did only single-celled bacteria and amoeba exist for so long?

“There must have been other ecological and evolutionary mechanisms at play,” Mills said. “Maybe life remained microbial for so long because it took a while to develop the biological machinery required to construct an animal. Perhaps the ancient Earth lacked animals because complex, many-celled bodies are simply hard to evolve.”