Atmospheric oxygen declining from Earth’s atmosphere over last 800000 years, says study

Oxygen is gradually declining from the Earth's atmosphere over the last 800,000 years, according to a recent study conducted at the Princeton University US. It also revealed that the decline paced up during the last century mainly due to burning of fossil fuels.

A comprehensive data of over 30 years has been drafted by the researchers which also is the first ice-core based record of atmospheric oxygen concentrations over the past 800,000 years.

The record also revealed that oxygen level declined 0.7 per cent in comparison to the present concentrations level. Interestingly during the last 100 years, the rate boosted by 0.1 per cent due to the burning of fossil fuels resulting in the production of carbon dioxide.

The researchers used the measured ratios of oxygen-to-nitrogen found in air trapped in Antarctica ice, to compile the history of atmospheric oxygen level.

Although various models and indirect proxies floated in the past suggesting level of oxygen in the atmosphere, but no conclusion was derived weather oxygen concentrations were falling, rising or were stagnant over the past million years.

The average amount of carbon dioxide in the atmosphere too didn't deviate significantly during the decline in the atmospheric oxygen level, as it generally does in the individual ice age cycles.

Giving the reference, a postdoctoral research associate at Princeton University said, "The planet has various processes that can keep carbon dioxide levels in check, one such process known as “silicate weathering”, where carbon dioxide reacts with exposed rock to eventually produce calcium carbonate minerals, which trap carbon dioxide in a solid form."

Higher carbon dioxide level in the atmosphere gives rise to temperature and silicate-weathering rates are hypothesised to increase and remove carbon dioxide from the atmosphere rapidly. The study reveals that the extra carbon dioxide released due to falling oxygen levels in the atmosphere triggered silicate weathering, which settled carbon dioxide but oxygen kept on falling over the period of time.

“The oxygen record is telling us there’s also a change in the amount of carbon dioxide (that was created when oxygen was removed) entering the atmosphere and ocean,” said John Higgins, assistant professor at Princeton University.

Higgins added, “However, atmospheric carbon dioxide levels aren’t changing because the Earth has had time to respond via increased silicate-weathering rates.”

The research was published in the journal Science.