March 19, 2012
Earth’s Prehistoric Multiple Atmospheres
Earth´s early atmosphere may have flipped between two sates before oxygenation, according to a new study.
Researchers at Newcastle University have published these findings in the journal Nature Geoscience. They found Earth´s early atmosphere would switch between a hydrocarbon-free state and a hydrocarbon-rich state. This kind of atmosphere, according to the researchers, is similar to that of Saturn´s moon, Titan.Referring to the two states as “organic haze” and “haze-free”, the researchers say in the journal that intense microbial activity played a large part in this type of atmospheric switching.
The study offers a new look at how the Earth´s surface may have reacted to these different atmospheres and how climates effect the Earth´s environments.
Dr. Aubrey Zerkle from the School of Civil Engineering and Geosciences at Newcastle University led the atmospheric study. According to Zerkle, “Models have previously suggested that the Earth´s early atmosphere could have been warmed by a layer of organic haze. Our geochemical analyses of marine sediments from this time period provide the first evidence for such an atmosphere.”
What Zerkle´s team found next was a bit of a surprise for them, and introduced a new theory on how the Earth´s atmosphere operated before oxygenation.
“However, instead of evidence for a continuously ℠hazy´ period we found the signal flipped on and off, in response to microbial activity.
“This provides us with insight into Earth´s surface environment prior to oxygenation of the planet and confirms the importance of methane gas in regulating the early atmosphere.”
Dr. Zerkle studied the geochemistry of 2.5 billion year old marine sediments in the area that is now South Africa. Joined by Dr. James Farquhar at the University of Maryland and Dr. Simon Poulton at Newcastle University, Dr. Zerkle discovered evidence of oxygen producing microbes in the oceans. However, this evidence also shows little of this oxygen actually made it into the atmosphere.
Paired with other evidence, the research team suggest Earth´s atmosphere may have switched repeatedly from a hydrocarbon rich state, or “hazy” atmosphere and a “haze-free” hydrocarbon-free state. Backing up the evidence in this study are ancient atmospheric models performed by NASA colleagues. These models demonstrate the effect of early methane levels on the Earth´s atmosphere.
Once oxygenation occurred on Earth´s surface, this flip-flopping atmosphere came to an end. The differences between the hazy and haze-free states were not all that different from one another, and each state offered a stable atmosphere, according to the study.
“What is most surprising about this study is that our data seems to indicate the atmospheric events were discrete in nature, flip-flopping between one stable state into another,” explains co-author Dr Farquhar.
“This type of response is not all that different from the way scientists think climate operates today, and reminds us how delicate the balance between states can be.”
In addition, this study also provides scientists with insights on how other types of atmospheres are born, as well as the effects these kinds of atmospheres have on the environment. Professor Mark Thiemans, Dean of Physical Sciences at the University of California San Diego added “Another important facet of the work is that it provides insight into the formation of atmospheric aerosols, particularly organic ones.
Besides the obvious importance for the evolution of the atmosphere, the role of aerosol formation is one of the most poorly understood components in the present day climate models. This provides a new look into this process that is quite new and valuable.”