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Sponges were most likely the first animals to evolve who helped in oxygenating the earth's oceans, according to a new study. The findings are the contrary to the traditional view that a rise in oxygen was responsible for their development. 

The research is also contesting the conventional belief that oxygenation of the atmosphere and oceans was a pre-requisite for the evolution of the complex life forms. 

"There had been enough oxygen in ocean surface waters for over 1.5 billion years before the first animals evolved, but the dark depths of the ocean remained devoid of oxygen. We argue that the evolution of the first animals could have played a key role in the widespread oxygenation of the deep oceans. This in turn may have facilitated the evolution of more complex, mobile animals," said professor Tim Lenton of the University of Exeter, who led the new study, according to physics.org. 

For their study, researchers considered the mechanisms in which the deep ocean could have been oxygenated during the Neoproterozoic Era (from 1,000 to 542 million years ago) without requiring an increase in atmospheric oxygen.

″This study provides a plausible mechanism for ocean oxygenation without the requirement for a rise in atmospheric oxygen. It therefore questions whether the long-standing belief that there was a major rise in atmospheric oxygen at this time is correct. We simply don't know the answer to this at present, which is ultimately key to understanding how our planet evolved to its current habitable state. Geochemists need to come up with new ways to decipher oxygen levels on the early Earth,″ added professor Simon Poulton of the University of Leeds, who is a co-author of the study.

The study has been published in the leading journal Nature Geoscience.