“Snowball Earth” events are some of the most dramatic climatic events in our planet’s history and have only occurred a handful of times, lasting for millions of years and followed by dramatic warming. New research from the University of Washington provides insight into how the last Snowball Earth event ended, shedding light on why it preceded a dramatic expansion of life on Earth, including the emergence of the first animals. The study, published in Nature Communications, focuses on ancient rocks known as “cap carbonates,” which formed as the glacial ice thawed about 640 million years ago.
Cap carbonates are layered limestone or dolomite rocks found in over 50 global locations and are thought to have formed as the Earth-encircling ice sheets melted, causing significant changes in atmospheric and ocean chemistry. These rocks contain information about Earth’s atmosphere and oceans, such as changing levels of carbon dioxide and ocean acidity. Understanding their formation helps explain the carbon cycle during periods of dramatic climate change and provides hints about the evolution of life on Earth, particularly why more complex life forms followed the last Snowball Earth.
Senior author David Catling, a UW professor of Earth and space sciences, notes that the billion years leading up to Snowball Earth were called the “boring billion” due to the simplicity of life on Earth in the form of microbes and algae. However, after the Snowball Earth events, animals appeared in the fossil record, indicating a significant shift in Earth’s biodiversity. The study’s framework provides a connection between the Snowball Earth events and the emergence of complex life forms, modeling chemistry and geology during three phases of the event.
During Snowball Earth’s peak, the thick ice reflected sunlight, but some open water areas allowed exchange between the ocean and atmosphere. As carbon dioxide built up in the atmosphere, global temperatures rose, melting the ice and allowing rainfall to reach the Earth. This led to freshwater flowing into the ocean and joining a layer of glacial meltwater floating over the denser, salty ocean water, slowing down ocean circulation. However, ocean churning later resumed, allowing mixing between the atmosphere, upper ocean, and deep ocean to return to normal.
The study predicts important changes in the environment as Earth recovered from the Snowball Earth period, impacting the temperature, acidity, and circulation of the ocean. Understanding these changes helps researchers confidently determine how they affected Earth’s life, providing insight into how life may have evolved after the tumultuous events of Snowball Earth. Future research will focus on how pockets of life that may have survived the Snowball Earth and its aftermath could have evolved into the more complex life forms that emerged soon after. Funding for the research was provided by the National Science Foundation and NASA, including a grant from the NASA Astrobiology Program to the UW’s Virtual Planetary Laboratory.
