ODENSE, Denmark, Feb. 17 (UPI) -- The first, most primitive animals may have thrived on Earth in water that contained almost no oxygen, Danish scientists say.
Researchers at the University of Southern Denmark say the finding suggests the rise of animals could have created our modern, oxygen-rich oceans, rather than oxygen-rich oceans triggering the initial rise of animals.
It challenges the standard view that the evolution of animals was delayed by a lack of sufficient oxygen for them to breathe, while it strengthens a theory the first animals may have helped raise oxygen levels, they said.
The scientists collected breadcrumb sponges (Halichondria panicea) from oxygenated waters in a Danish fjord, then kept them in an aquarium from which the oxygen was slowly removed.
Even with just 1/200th of the oxygen currently found in the atmosphere, the sponges survived, and if modern sponges can live with little oxygen, early animals probably could too, the scientists said.
"There are still many researchers who contend that animals could not have arisen until oxygen levels became relatively high," study leader Danial Mills told NewScientist.com. "Our results challenge that."