First life needed much less oxygen to survive than previously believed, according to PhD student Daniels Mills from the Nordic Centre for Earth Evolution at the University of Southern Denmark.

By studying a sea sponge resembling one of the very first creatures on Earth, Mills found that sponges could live, breathe, eat and grow bigger with only 0.5 percent of the amount of oxygen in the atmosphere today.

Rising oxygen levels in the atmosphere were believed to be the reason why the first complex life forms emerged half a billion years ago, but the new discovery points towards a gap in that theory.

"We wanted to know why animal life emerged 635 to 800 million years ago. Why not two million years ago?" Mills told online science magazine Videnskab.dk.

"It turns out that oxygen wasn't the limiting factor holding back the evolution of animals as they needed much less oxygen in the atmosphere than previously held," he said.

His theory suggests that there is another reason why life evolved relatively late in Earth's history, since there was plenty of oxygen for the first life forms to survive.

New light on extra-terrestrial life
The discovery was published in the PNAS science journal on Tuesday and may also cast new light on the search for life on other planets. 

"If oxygen wasn't so important for complex life to evolve on Earth, it may not be that important in the rest of the universe either," he said.

Scientists from Denmark seem to be riding a wave of groundbreaking scientific discoveries lately. In February, genetic researcher Eske Willerslev received worldwide media attention for his discoveries relating to the ancestors of Native Americans and the cause behind Ice Age mass extinctions.