Our planet has been driven to environmental extremes at many times in its history, and many plants and animals – including humans – have demonstrated they can survive less than ideal conditions. The last major ice age hit its peak 20 to 26 thousand years ago, and allowed humans to cross icy bridges between continents. That ice age, however, didn’t encompass the entire planet. Our world hasn’t been a complete snowball since before the ages of reptiles and dinosaurs. Infact, the last global ice age took place 635 million to 650 million years ago. And when a planet goes from entirely governed in snow and icy to not entirely frozen, it gets really gross for a while.
New research appearing in Proceedings of the National Academy of Sciences and led by Tian Gan, uses lithium isotopes to identify just when our world became a slushy mess.
Essentially, the early earth, when our world only had microscopic life, went through a period of extremely low carbon dioxide levels, and this led to our world freezing. This led to super salty water beneath a deep layer of ice.
Volcanism, however, slowly released carbon dioxide into the atmosphere until, one geologic epoch, the amount of greenhouse heating from that carbon dioxide was sufficient to start melting the ice. This led to fresh water from the melt pooling on the surface of the super salty oceans. This difference in chemistry led to differences in the chemical composition of rocks that formed in different places… a chemical difference Gan’s paper documents.
References
- When Earth was Slushy (Virginia Tech)
- Gan, T., Tian, M., Wang, X. K., Wang, S., Liu, X. M., Jiang, G., … & Xiao, S. (2024). Lithium isotope evidence for a plumeworld ocean in the aftermath of the Marinoan snowball Earth. Proceedings of the National Academy of Sciences, 121(46), e2407419121. https://doi.org/10.1073/pnas.2407419121