Cosmology: snowball Earth's last disappearance (Introduction)

by David Turell , Thursday, February 27, 2025, 15:47 (7 days ago) @ David Turell

A new view of our snowball period:

https://theconversation.com/giant-glaciers-pulverised-earths-ancient-rocks-setting-the-...

"During the Cryogenian, our planet was plunged into a series of deep freezes when enormous glaciers flowed across the globe.

"In new research published in Geology, we show that these crushing rivers of ice, sometimes kilometres deep, pulverised the planet's rocky surface like enormous bulldozers.

"When the ice eventually thawed, the ground-up minerals washed into the oceans where they may have provided the nutrients needed for the evolution of complex life.

***

"Nobody is sure exactly what triggered these deep-freeze events, though scientists have proposed a range of possibilities. One key may have been a significant decline in atmospheric greenhouse gases, particularly carbon dioxide

***

"As ice sheets advanced toward the tropics, they reflected more sunlight back into space, leading to further cooling. These processes together caused ice to spread rapidly until the planet was almost entirely frozen.

"Volcanic activity may have played a crucial role in ending these ice ages. As glaciers covered the planet, interactions between Earth's crust, oceans and atmosphere slowed dramatically. As a result, when volcanic eruptions injected CO2 into the atmosphere, it would not have been re-absorbed but rather accumulated over millions of years.

"These high levels of CO2 created a runaway greenhouse effect, warming the planet and eventually melting the ice. The resulting thaw caused rapid sea level rise and an influx of nutrients into the oceans.

"Distinct rock formations were created during this abrupt climate change, as the chemistry of the oceans responded to the new conditions. The surge of nutrients may have contributed to a cascade of biological changes, possibly setting the stage for the rise of complex life.

***

"Snowball Earth events were associated with a pronounced increase in older, deeper crust being exposed and ground down under kilometres of ice.

"As the glaciers retreated during thaw periods, massive outflows of melt water transported mineral grains that had been trapped and stabilised under the ice. Once exposed to liquid water, fragile minerals dissolved, releasing chemicals.

"This process – like the changes in the atmosphere – would have changed the chemistry of the oceans. The glacial retreat help shaped the distribution of elements critical to ocean ecosystems.

***

"On shorter timescales, however, human activities have become the dominant force driving climate change.

"While Earth itself will endure, the survival of complex human societies depends on our actions today. We are passengers on an extraordinary "spaceship Earth", a planet that recycles its chemical building blocks through dynamic geochemical cycles, using matter originally forged in ancient stars."

Comment: for life to appear using oxygen and nitrogen, the main components of our atmosphere, the geologic and glacial factors had to evolve and make a life-friendly Earth.