New research challenges the origin of animals on earth

(scienceinfo.net) - The theory of animal origin has been challenged: some animals really need some oxygen.

One of the most powerful prerequisites for science is that: the complex life on Earth only grows when the concentration of oxygen in the atmosphere has increased almost to its present level.

However, recent research on a sponge in a fjord in Denmark shows that complex life does not require high concentrations of oxygen to survive and grow.

The origin of complex life is one of the greatest mysteries of science. How small primitive cells can develop into diverse high-end life forms that exist on Earth today. Explained popularly in all textbooks, it is thanks to oxygen. Complex life has evolved because atmospheric oxygen levels began to increase by 630 to 635 million years ago.

However, recent research on a sponge from Kerteminde Fjord shows that the explanation needs to be reviewed. Sponge studies show that animals can live and grow even when oxygen sources are very limited.

Halichondria panicea sponge was used in an experiment at the University of Southern Denmark

The truth is that animals can live and grow when the atmosphere contains only 0.5% oxygen in the atmosphere today.

'Our studies show that the origin of animals is not hampered by low oxygen levels,' said Daniel Mills , an associate professor at the Nordic Earth Evolution Center at the University of Southern Denmark.

Together with Lewis M.Ward from the California Institute of Technology, he is the lead author of a research paper on this content in PNAS magazine.

Approximately half a billion years ago, the first complex life forms - animals - developed on Earth. Billions of years ago, life consisted of life forms with simple single-celled structures. The emergence of animals coincided with a significant increase in atmospheric oxygen concentrations, and it seems to be evidence that science links these two events and concludes that oxygen levels have increased. leads to the evolution of animals.

'But no one has ever checked how much animals need oxygen levels - at least I don't know. So we decided to find the answer, ' said Daniel Mills.

The animals that live most like the first animals on Earth are sponges.The Halichondria panicea sponge lived only a few meters from the Marine Biology Research Center of the University of Southern Denmark at Kerteminde, and it was here and Daniel Mills took out the individuals to use for his research. .

'When we put sponges in the lab, they continue to breathe and grow even when the oxygen concentration reaches 0.5% of the current atmospheric concentration, ' Daniel Mills said.

This is a lower concentration than the oxygen concentration we thought was necessary for animal life.

The big question now is: 'If low oxygen levels did not prevent evolutionary animals - what did it do? Why does life consist only of protozoan bacteria and primitive single-cell amoeba for billions of years before everything suddenly bursts and complex life arises " ?

'There must be other ecological and evolutionary mechanisms. Perhaps life is in the form of bacteria for so long because it takes time to develop the biological mechanism needed to build an animal. Perhaps the ancient earth lacks animals because complex, multicellular bodies are difficult to develop , "Daniel Mills surmised.

His colleagues from the Nordic Earth Evolution Center once demonstrated that oxygen levels have actually increased significantly at least once before complex life developed. Although then there was a lot of oxygen, it did not lead to the development of complex life.