Evrim Yazgin
Cosmos science journalist
Scientists are coming closer to understanding the impact of the two periods known as “Snowball Earth,” on the evolution of life, and in particular, complex life.
Earth was covered in ice twice during a period called the Cryogenian, 720 to 635 million years ago (mya). The first, called the Sturtian glaciation, lasted 56 million years. The duration of the second, however, called the Marinoan, is less well understood.
“The duration of the Marinoan glaciation (4 to 15 million years) currently has 11 million years of uncertainty”, write the authors of the new paper published in the journal Proceedings of the National Academy of Sciences.
A team of geologists analysed ancient glacial rocks in Namibia to narrow down the duration of the Marinoan.
Namibia today sits on the west coast of the African continent and has vast swathes of desert. But more than 600 mya this region – like everywhere on Earth – was coated in a layer of ice.
Drones allowed the team to map sedimentary layers in the Namibian rock. The mapping revealed the periods in which there was little vertical shift coinciding with periods of time where glaciers did not move much.
The team then used isotopic dating of ash layers just before the Marinoan. This ash is likely from the volcanic activity which caused the global ice age.
They found that the Marinoan started 639 mya and lasted about 4 million years.
The first fossil evidence of complex life emerges after the 2 periods of Snowball Earth, suggesting a relationship between the thawing of the global ice age and the evolution of multicellular organisms.
The authors of the new study also suggest the difference in time between the Sturtian and Marinoan glaciations might help explain this evolutionary process. Further research may further reveal the link.
“The short duration of the Marinoan glaciation may have been essential for the survival and evolution of animals and illustrates an additional path toward habitability on exoplanets,” they write.
