What happens when Earth’s carbon cycle is altered? Looking back 720 million years might give us a clue.
[social_buttons]A new study led by researchers from Princeton University suggests that a “snowball Earth” period created a significant change in the planet’s carbon cycle which in turn may have produced even more ice-ages.
Understanding the causes and effects of the shift in the planet’s carbon cycle – the manner in which carbon moves through the oceans, the biosphere and the atmosphere – is vital for understanding how Earth’s climate can change, and how the planet might change again under a similar or smaller shift in the carbon cycle.
“The Neoproterozoic Era was the time in Earth history when the amount of oxygen rose to levels that allowed for the evolution of animals, so understanding changes to the carbon cycle and the dynamics of the Earth surface at the time is an important pursuit,” said Princeton graduate student Nicholas Swanson-Hysell, the first author on the paper.
The “snowball Earth” theory posits that Earth’s surface was entirely frozen during the Neoproterozoic Era which lasted from 1,000 million years ago to 542 million years ago, and included the Cryogenian period in which a possible three full glaciations are suggested: the Kaigas, the Sturtian and the Marinoan, though the Kaigas is question marked by conflicting evidence.
The Cryogenian period is significant in Earth’s history as it included several repeated ice ages, which become even more significant considering that it had been 1.5 billion years since the planet had last experienced an ice age before the Sturtian glaciation took place.
The Princeton researchers collected samples of limestone from Central and South Australia dating back to the Tonian and Cryogenian periods of the Neoproterozoic Era and used a technique known as isotope analysis to learn how the carbon cycle was acting in those periods. Their results showed that a massive shift in the carbon cycle had taken place.
“The disturbance we’re seeing in the Neoproterozoic carbon cycle is larger by several orders of magnitude than anything we could cause today, even if we were to burn all the fossil fuels on the planet at once,” said Adam Maloof, a research team member and assistant professor of geosciences at Princeton.
Building on a hypothesis put forward by Massachusetts Institute of Technology geophysicist Daniel Rothman’s 2003 theory that suggested a massive build up of carbon in the oceans could have led to the shift in the carbon cycle, the Princeton scientist attempted to explain how the accumulation of large amounts of organic carbon in the ocean could have lead to the observed carbon disturbance later in the Neoproterozoic period.
“The new carbon isotopic data shows a whopping … downshift in the isotopic composition of carbonate, possibly the largest single isotopic change in Earth history, while the isotopic composition of organic carbon is invariant,” said Rothman, who was not part of the research team. “The co-occurrence of such signals is enigmatic, suggesting that the carbon cycle during this period behaved fundamentally differently than it does today.”
They posit that the Sturtian glaciation was global in scope and that the passage of the glaciers across the surface of the continents would have removed the weathered material and debris which had accumulated over the 1.5 billion years of the preceding age subsequently freeing up large amounts of bedrock to the carbon dioxide in the atmosphere. This would have allowed the atmosphere to further weather the surface of the planet, delivering large amounts of iron into the oceans which, if not eaten by the bacteria, could have resulted in a massive oceanic reservoir of carbon dioxide.
These reactions would also have removed a measure of carbon dioxide from the atmosphere into the oceans, lowering global temperatures and creating an environment conducive to further glacial events.
The increasing levels of oxygen would have eventually lead to a massive oxidation of the carbon dioxide, removing the excess organic carbon from the oceans and returning the carbon cycle back to its original state. This theory also helps in understanding the massive diversification of animal life at the end of the Neoproterozoic era.
Source: Princeton University