A group of researchers have claimed that a minor jump in oxygen levels facilitated the early evolution of animals.
The discovery questions the theory that a dramatic change in oxygen levels might have been responsible for the appearance of complicated life forms like whales, sharks, and squids evolving from less complicated life forms, such as microorganisms, algae, and sponges.
According to the researchers, oxygen levels in water and atmosphere rose at lower levels than was thought necessary to trigger life changes.
Benjamin Gill, an Assistant Professor in the College of Science, suggested that about 635 million to 542 million years ago, the Earth passed some low, but critical, threshold in oxygenation for animals.
Gill added that threshold was in the range of a 10 to 40 percent increase, and was the second time in Earth's history that oxygen levels significantly rose.
The scientists estimated oxygen levels by analysing iron found in shale rock, which was once mud on ancient seafloors. The location and amounts of iron in the rock gave important clues about ancient ocean water chemistries over time.
The study is published in the journal Nature.
