SHAFAQNA- A new study from Princeton University confirms the Earth has lost a measurable amount of oxygen — though not nearly enough to cause an problems for humans.
The new study shows global O2 levels dropped by about 0.7 per cent, over the course of 800,000 years. Writing in Science, the researchers say over that period, oxygen sinks — factors that consume oxygen — were about two per cent larger than oxygen producers.
“Every thousand years or so, all of the O2 [in Earth’s atmosphere] is turned into water and then back into O2, but there’s an ever so slight leak over time, in terms of extra production or consumption,” lead author Daniel Stolper, a geologist at Princeton University, told Gizmodo.
Stolper is also clear that humans needn’t start stocking up on O2 tanks, as the drop is negligible.
“To put it in perspective, the pressure in the atmosphere declines with elevation,” he told Live Science. “A 0.7 per cent decline in the atmospheric pressure of oxygen occurs at about 100 meters above sea level — that is, about the 30th floor of a tall building.”
Drilled Antarctic ice containing trapped air bubbles. Image: CSIRO/Wikimedia Commons
Oxygen, commonly rendered as O2, makes up 20 per cent of Earth’s atmosphere, along with 78 per cent nitrogen and about two per cent other gases, including argon and carbon dioxide.
That doesn’t sound like much, but it seems to have been more than enough for humans, and in eons past, oxygen levels were much lower.
We owe its presence in our atmosphere to organisms known as cyanobacteria, which began producing oxygen through photosynthesis (Astrobiology Magazine says the process may have begun as early as 3.5 billion years ago). They continued to produce O2 until a tipping point that began 2.3 billion years ago, when their output began to exceed oxygen sinks’ capacity to absorb.
Cyanobacteria. Source: Josef Reischig/Wikimedia Commons
Scientists can measure atmospheric composition using ice cores drilled from the ancient ice sheets of Greenland and Antarctica, containing trapped air bubbles going back hundreds of thousands of years.
As for why the oxygen seems to have declined, Stolper and his colleagues have two main hypotheses.
First, Stolper told Gizmodo increased erosion over the past few hundred thousand years could have exposed more material to the atmosphere, acting as an O2 sink via oxidization. A slight decline in Earth’s temperature over the same period may also be responsible: Atmospheric oxygen dissolves easier in cooler ocean waters.