It is a popular notion within the scientific community that lifeforms oxygenated the planet to support life as we know it is today. However, new research suggests otherwise.
According to the study led by Dr. Philip Pogge von Strandmann of UCL Earth Sciences, oxygen levels in the oceans gradually increased over 600 million years ago. This gradual increase took at least 100 million years for the oxygen levels in the ocean and the atmosphere to increase to the point that can support life on the planet.
The study, titled "Selenium isotope evidence for progressive oxidation of the Neoproterozoic biosphere," was published in Nature Communications on Friday. The study was conducted to determine how evolution of the planet's climate relates to evolution of life, noting that answering how life has modified the climate and why the planet has been habitable is critical in understanding the climate system and life on Earth.
The researchers studied marine shales estimated to be from 770 to 520 million years ago, the samples of which were taken from different locations across Canada, China and the U.S. The researchers placed tracers that measure selenium isotopes on the subjects.
"We took a new approach by using selenium isotope tracers to analyse marine shales which gave us more information about the gradual changes in oxygen levels than is possible using the more conventional techniques used previously," said Strandmann.
Upon scrutinizing their subjects, the researchers were surprised to find out that it took about 100 million years for oxygen levels in the atmosphere to reach less than 1 percent to more than 10 percent of today's oxygen levels. The study suggests that at least three glaciations had to occur before the planet was properly oxygenated to support life, therefore debunking the theory that the planet became more oxygenated as animal-like lifeforms continued to increase.
The study's co-author Professor David Catling likened oxygen to a fuse that took its time to trigger the explosion of animal life. He added that tracking the increase of oxygen levels is the first step towards understanding its progression, noting that an idea of geologic controls on oxygen levels can help scientists determine whether or not animal-like life might exist elsewhere in the galaxy.
