A tube sponge with sea cucumbers and cup corals.
A tube sponge with sea cucumbers and cup corals. Photo by Wikicommons / Nick Hobgood
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Sea sponges may have been the precursor to all life on earth, including human life, according to new research.

A new paper published in the Nature Geoscience journal says that sea sponges may have added oxygen to the deep ocean, helping forge an environment where more complex life forms could evolve, Discovery News reported Monday.

Earlier this year, research found that the earliest sponges could have survived in waters with very little oxygen. The research presented in this latest paper builds on this.

“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,” said a press release from Tim Lenton of the University of Exeter, according to Discovery News. “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,” the press release said.

According to DNA analysis, sea sponges first emerged at least 700 million years ago - a time when the oceans contained little oxygen. Oxygen levels in the oceans rose between 700 and 600 million years ago, and animal fossils have been found dating to 650 million years ago.

The above is some of the evidence that supports the theory. The way that sponges feed is further evidence, Discovery News said. As they feed, water circulates through sponges, carrying nutrients, and also particles of organic matter. All those years ago, these particles would have included dead microbial matter that eats up oxygen as it rots. Removing these rotting particles from the ocean would have led to increased oxygen in the water, according to researchers.

With more oxygen, more complex life forms would have been able to emerge, including animals that prey on each other, and eat each other, according to Discovery News. This would have paved the way for today's food webs and the marine ecosystem.

The theory that earth creatures, including humans, first evolved from underwater ones is widely accepted, Discovery News noted, adding that scientists believe sponges may have been an "Animal Eve" that led to the evolution of all animals today.

The research also solves the riddle of whether oxygenated waters predated the humble sponge, or the other way around. “The effects we predict suggest that the first animals, far from being a passive response to rising atmospheric oxygen, were the active agents that oxygenated the ocean around 600 million years ago,” the researchers said. “They created a world in which more complex animals could evolve, including our very distant ancestors."