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 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 time was likely caused by huge amounts of carbon dioxide from volcanoes and 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

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

During the Marinoan glaciation, signs of ice show that Earth had a very cold time. Big sheets of ice grew and shrank in 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 melted, carbon dioxide built up in the air, helping to warm the planet again.

Evidence

Scientists have found clues that show the Marinoan glaciation happened in places like China, the Svalbard archipelago, and South Australia. In Guizhou Province, China, they found glacial rocks under and over layers of volcanic ashes that contained special minerals called zircon. These minerals help scientists learn how old the rocks are. In South Australia, old glacial deposits were found, confirmed by studying carbon isotopes and rock formations. In the northeastern Svalbard archipelago, two special layers in the rock show when the Marinoan glaciation began and ended. In Uruguay, evidence like dropped stones and rock layers also points to this ancient ice age.

According to researchers Eyles and Young, the Marinoan glaciation was a 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. 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 sea plants called benthic macroalgae managed to survive. This tells us that there were still some places near the coasts where these plants could live, especially where they could get sunlight.