Marinoan glaciation

The Marinoan glaciation was a time when huge sheets of ice covered much of the Earth. It is also called the Varanger glaciation. This glaciation was part of a larger time period known as the Marinoan Epoch.

Scientists think this glaciation began no earlier than 654.5 million years ago and ended around 632.3 million years ago, during what is called the Cryogenian period. The name Marinoan comes from the Adelaide suburb of Marino, where researchers Douglas Mawson and Reg Sprigg first described it in 1950.

Some believe that during this time, the whole planet may have been covered in ice, an event called the Snowball Earth. The end of this icy period was likely caused by huge amounts of carbon dioxide released from volcanoes, along with gases from places where ice and soil were trapped. This warming helped the Earth move out of the glaciation.

Origin of name and history of terminology

The name Marinoan comes from the Adelaide suburb of Marino in South Australia. In 1950, scientists Douglas Mawson and Reg Sprigg used this name to describe rocks from a certain time in the Adelaide area. They noticed signs of an icy period, which they called the Elatina glaciation after a place called Elatina where they found evidence.

Over time, the term Marinoan glaciation was used worldwide for similar icy periods. Recently, some scientists prefer using the name Elatina glaciation again because they are not sure if all these icy periods around the world happened at exactly the same time.

Cryogenian Snowball Earth

Further information: Cryogenian, Snowball Earth, and Neoproterozoic

Scientists think that long ago, during a time called the Neoproterozoic, Earth went through several periods when it froze over. These big icy times are called "Snowball Earth" because, in these periods, it is believed Earth was covered in thick ice. One of these icy times was the Marinoan glaciation. It was not as long as another big icy time called the Sturtian glaciation, but it still covered the whole world in ice.

During the Marinoan glaciation, signs of ice show that Earth had one of its toughest ice ages. Big sheets of ice grew and shrank in many steps, maybe even reaching places near the equator. Even though Earth might not have been completely covered in ice, the ice was still very widespread. When the ice finally melted, it is thought that lots of carbon dioxide built up in the air, helping to warm the planet again.

Evidence

Even though much evidence has been lost through geological changes, scientists have found clues showing the Marinoan glaciation happened in places like China, the Svalbard archipelago, and South Australia. In Guizhou Province, China, they discovered glacial rocks under and over layers of volcanic ashes that contained special minerals called zircon. These minerals help scientists figure out how old the rocks are. In South Australia, similar old glacial deposits were found, confirmed by studying carbon isotopes and other unique rock formations. In the northeastern Svalbard archipelago, two special layers in the rock show the start and end of the Marinoan glaciation. In Uruguay, more evidence like dropped stones and special rock layers also points to this ancient ice age.

According to researchers Eyles and Young, the Marinoan glaciation was a second cold period during the Neoproterozoic era (about 680–690 Ma), happening in the Adelaide Geosyncline. They believe it happened after another glaciation called the Sturtian, separated by lots of rocks that don’t show signs of ice. This cold time might match what was found in the Ice Brooke formation in the northern Cordillera.

Effects on life

During the Marinoan glaciation, some types of sea plants called benthic macroalgae were able to survive. This shows that there were still places along the coasts of continents where these plants could live, especially in areas where sunlight reached.