After a couple of months of absence, GeoLog is once again hosting the Geosciences column. This month we have no less than two posts highlighting recent research in the Earth sciences. In the first of this month’s columns, Amanda Gläser-Bligh writes about recent research on the regulation of the air published in the EGU journal Solid Earth.
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What if the Earth had a thermostat that kept temperatures in the correct range to maintain life? In a recent paper published in Solid Earth, Euan Nisbet of London’s Royal Holloway and his collaborators propose just that.
Despite ups and downs in the atmospheric temperatures over geologic time, the Earth system seems to have maintained an equilibrium temperature of around 15°C. The global temperature appears to be able to correct itself up and down, much like an airplane constantly corrects its route, or a thermostat maintains a given temperature in a room. But how is the atmosphere being regulated on the planet, and who or what is selecting the temperature? An enzyme named rubisco seems to hold the answer.
What regulates the atmospheric composition of the Earth? (Photo: The sky from a plane after sunset, by Konstantinos Kourtidis. Distributed by EGU under a Creative Commons licence.)
Rubisco is one of the most commonly occurring enzymes on the planet: “When you eat your breakfast, you are most likely eating some rubisco,” Nisbet points out. The enzyme occurs in most green matter, having the important role of regulating CO2 intake to be used in photosynthesis, which in turn helps control atmospheric pressure by changing the CO2:O2 ratio.
The enzyme is responsible for the amount of carbon capture from CO2, and it is possible that rubisco’s selection of CO2 in preference to O2 controls the amounts of CO2 taken up by plants and algae, which is changing according to atmospheric conditions. This implies that rubisco itself determines the balance of CO2 and O2 in the air. The theory proposed by Nisbet and collaborators is that natural selection comes into play and causes the photosynthesizing organisms to pull down enough, but not too much, CO2 out of the atmosphere. This creates what is known as the Goldilocks effect: a planet that is not too hot and not too cold, but just right to sustain life.
There is a strong debate as to whether the atmospheric composition has been controlled by organic or inorganic elements. Nisbet and his team claim that while the system is biologically led, the process is a mixture of the two with inorganic chemistry working together with underlying biological trends.
Together with the changes occurring in the Sun, which was much weaker in the past, the greenhouse effect has reduced over time to compensate for this increase in solar temperatures. The suggestion is that rubisco evolution is the main driver of this shift and has created a stable system to maximize biological survival.
Additionally, because rubisco is a biological control, the response to challenging changes in atmospheric conditions (such as a massive volcanic outpouring of CO¬2) can occur rather rapidly when compared to inorganic processes, such as silicate erosion which also absorbs CO2.
To view what the scientific community had to say about the paper, check the article’s interactive discussion. ‘The regulation of the air: a hypothesis’ is the all-time most commented paper on Solid Earth Discussions.
By Amanda Gläser-Bligh, geologist and freelance writer
