A new study has unveiled that a small rise in oxygen levels had led to early evolution of animals. The study challenges the early thought that a dramatic rise in oxygen levels might have facilitated the appearance of animals like whales, sharks and squids.

The researchers noticed that oxygen levels have increased in the water and atmosphere, but they have increased at lower levels than what were thought to be necessary for initiating life changes. Benjamin Gill, an assistant professor of geoscience in Virginia Tech’s College of Science, was of the view, “We suggest that about 635 million to 542 million years ago, Earth passed some low, but critical, threshold in oxygenation for animals”.

Gill said that the threshold might have been in the range between 10 to 40%. It was also the second time when oxygen levels increased significantly in earth’s history. The study researchers have assessed oxygen levels by assessing iron found in shale rock.

Two factors- location and amount of iron in the rock provided important hints to the researchers to know about ancient ocean water chemistry over time. A small jump in oxygen levels allowed animal evolution to start breathing air.

For the research, rock data from across the world was gathered, assessed, compiled and statistically modeled. Many organisms on earth need oxygen to produce energy and perform life functions.