It is likely that some 720 million years ago, during the so-called Cryogenian Era, Earth was completely frozen over.
If our planet trapped the same fraction of sunlight some 4 billion years ago as it does today, then its surface temperature would have been approximately 20 degrees Kelvin colder. Four billion years ago, our solar system’s star, the sun, shined at only three-quarters of its current luminosity.
Was our planet ever completely frozen?
Based on the evidence we have gathered to this day, it is likely that some 720 million years ago, during the so-called Cryogenian Era, Earth was completely frozen over. Two supposed major global glaciations characterized the Cryogenian. These are called the Snowball events of the Sturtian glaciation and the Marinoan glaciation. Both took place 717-660 million years ago and 645-635 million years ago.
The problem is that although we have tentative evidence to support the Snowball Earth episodes, not everyone agrees with them since they are very poorly understood. Nonetheless, as explained by the Book “Life in the Cosmos” by Harvard Astronomer Professor Avi Loeb and postdoc student Mansavi Lingam, both the Sturtian glaciation and the Marinoan glaciation were likely essential for the development of a variety of animal life for various reasons.
The end of the Sturtian and Marinoan
The end of these glaciation periods was linked to heavy melting glaciers. This fed the oceans with increased nutrients. Phosphate, for example, was “injected” into Earth’s oceans, which likely enabled algae’s rapid growth. The algae consequently served as a possible food source for oceanic animals. More food equals easier diversification. This has been validated by the study of sedimentary rocks that point towards increased phosphate availability during the end of the Sturtian and Marinoan glaciations.
Why this matters
This is important because the Snowball Earth episodes were a sort of environmental trigger for a rise in oxygen levels in Earth’s oceans and atmosphere. This means that the extensive glaciations were practically a delivery system that dumped essential nutrients into the ocean. Consequently, many complex ecosystems were born. The Snowball Earth events took place just before a sudden rise of multicellular life forms. Scientists know this as the Cambrian explosion. Scientists now believe that the most recent Snowball Episode triggered a boom in life and the evolution of multicellularity.
Check out the below video, which offers insight into Snowball Earth.