There was an ice age, called the Marioan ice age or 'Snowball Earth', that happened around 600 million years ago and there is a theory of why and how it came to such a sudden and abrupt end. Scientists say that it happened with "large amounts of methane, the bubbling through ocean sediments, a strong greenhouse gas, and from beneath the permafrost and heating the atmosphere."
Samples of cap dolostone in south China were found and that is the main physical evidence there is to support this theory. These are known to have less of the carbon-13 isotope than found in normal carbonate rocks. Dolostone is a type of sedimentary rock that consists of dolomite, a carbonate mineral and it is called 'cap' dolostone when it overlaps a glacial deposit. The theory states that these rocks formed when methane bubbled up from below and was oxidized by microbes, "with its carbon wastes being incorporated into the dolostone", causing the end of the ice age. This made sense because methane tends to be low in carbon-13 and if the carbon-13-depleted methane was turned into rock, that rock would also be low in carbon-13. However, this idea was quite controversial since there was no trace of previous isotopic evidence in carbonate rock as back in time as the ice age happened.
A team from the California Institute of Technology (Clatech) published an article in the journalNature saying it is wrong because of the testings they have done. Their data showed that the rock that was the main evidence that the theory was based on had formed millions of years after the ice age had ended and in temperatures so high that were unbearable for any living organism.
John Eiler, the Robert P. Sharp Professor of Geology and professor of geochemistry at Clatech, and one of the paper's authors, developed a technique used to tell the rocks' "story" that looked at the way the isotopes, like the carbon-13 in the dolostones, group together in crystalline structures like bone or rock. They proved that this grouping of isotopes in dependent to the temperature of the environment in which the crystals form; the hotter the temperatures are, the less grouping there is, and the colder the temperatures are, more grouping occurs.
"The rocks that we analyzed for this study have been worked on before," says Thomas Bristow, the paper's first author and a former postdoc at Caltech who is now at NASA Ames Research Center, "but the unique advance available and developed at Caltech is the technique of using carbonate clumped-isotopic thermometry to study the temperature of crystallization of the samples. It was primarily this technique that brought new insights regarding the geological history of the rocks."
Eiler says, "the carbon source was not oxidized and turned into carbonate at Earth's surface. This was happening in a very hot hydrothermal environment, underground." We know it happened at least millions of years after the ice age ended, and probably tens of millions. Which means that whatever the source of carbon was, it wasn't related to the end of the ice age."
This topic brings up many questions since scientists say that the only evidence there is, is the carbon-isotopic evidence of a Precambrian methane seep. Scientists are not just trying to find out how the Marinoan ice age ended, but also about the amount of methane of the Earth and the biogeochemistry of the ocean.
What interested me about this article was that, at first, when I read the title I though it was about the end of the world and I started reading the article, but then I realized what it was really about and it got me more interested. I think that it is fascinating how chemistry and geology are related because, in this case for example, they are connected by how the rock is formed and how a chemical reaction occurred for the ice age to have happened. Even though I did not understand some of the explanations about how the rock was formed since I have not studied chemistry in that level of depth, I found it quite an appealing subject and I want learn more about it. Learning about what happened 600 million years ago is very fascinating and if something like this happens again, in the future we might be going through another ice age...