It is generally accepted that in the distant past, the Earth was essentially covered in ice. This was when a global Ice Age occurred where the temperatures dropped dramatically (over the course of thousands, or even millions of years).
This type of event is believed to have happened because as more of the Earth is covered with ice, more of the sunlight gets reflected back out into space, which allows the Earth to get colder, and therefore the temperature drops and creates more ice.
This is a vicious cycle that on other planets may have left it covered in ice forever.
Over time, however, the CO2 levels built up on the Earth from volcanic eruptions and other sources. Since the water was frozen, it was unable to absorb the CO2, which led to a period of global warming. This slow and natural process eventually melted the ice, allowing water to weather the rocks, which is a key part of removing CO2 from the atmosphere.
It makes sense that between the time when the Earth was covered in ice and when the ice melted into oceans, there was a period where there was liquid water with lots of ice in it. Up until recently, however, very little was known about this period that could be called the ‘Slush Age.’ Paleoclimatologists, however, call it a “plumeworld ocean.”
A study on this time period was recently published in the journal Proceedings of the National Academy of Sciences. This study was done by Dr. Tian Gan who was at Virginia Tech at the time.
He worked with a team to analyze the ratio of lithium-6 to lithium-7 within the carbonate rocks that were left behind as the ice melted.
When glacial ice melts, it releases huge amounts of freshwater. This is where many lakes come from, but in the oceans, it can take hundreds of years for the freshwater to fully mix with the salt water of the ocean.
As the ice melted, the continental rocks began to be exposed to the surrounding environment for the first time since this massive ice age began. They were exposed to rain and other weathering effects, which allowed them to rapidly deposit sediments into the surrounding area. It is this sediment that the researchers used as clues to learn more about this time period.
The researchers looked at the levels of lithium 6 and lithium 7 in modern riverbeds and found that the amounts of each is separated by about 23%. In the deep ocean, however, that difference is just 8.3%.
As you move closer to land, however, that grows to be more similar to what is seen in modern rivers. Since the lithium ratios are determined almost exclusively by how much water is flowing off of the land, this allowed the scientists to essentially look back in time to see how and when the ice melted and mixed into the oceans.
The study took place in modern South China. The results supported their theory that showed that sea ice melted at the top first, creating a layer of fresh water over the salty ocean. This was then combined by plumes from the continents, which mixed various minerals, including lithium, into the freshwater at the surface of the oceans.
The study says that in this area, it occurred in three stages. First, the melted ice was the main source of fresh water on the oceans. Next, the melting plums added dramatically to that fresh water supply. Finally, the salt and fresh water were slowly mixed.
So, what does all of this mean? Gan briefly explained in a statement:
“Our results have important implications for understanding how Earth’s climate and ocean chemistry changed after the extreme conditions of the last global ice age.”
This can help to give insights into how the Earth changed in the past, and even what we may experience in the future.
Climate history is so fascinating!