A little over half a billion years ago, the first forms of complex life -- animals -- evolved on Earth. Billions of years before that life had only consisted of simple single-celled life forms. The emergence of animals coincided with a significant rise in atmospheric oxygen, and therefore it seemed obvious to link the two events and conclude that the increased oxygen levels had led 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," says Daniel Mills.
The living animals that most closely resemble the first animals on Earth are sea sponges. The species Halichondria panicea lives only a few meters from the University of Southern Denmark's Marine Biological Research Centre in Kerteminde, and it was here that Daniel Mills fished out individuals for his research.
"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," says Daniel Mills.
This is lower than the oxygen levels we thought were necessary for animal life.
The big question now is: If low oxygen levels did not prevent animals from evolving -- then what did? Why did life consist of only primitive single-celled bacteria and amoebae for billions of years before everything suddenly exploded and complex life arose?
"There must have been other ecological and evolutionary mechanisms at play. 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," says Daniel Mills.
【挑战动物起源理论 丹麦海绵需氧极少】相关文章:
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2020-09-15
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