11. Snowball Earth

What were the major continents and tectonic events during the Proterozoic Eon

During the Proterozoic Eon, several supercontinents formed, including Columbia (~1.8 Ga), Rodinia (~1.1 Ga), and Pannotia (~600 Ma). Plate tectonics drove mountain building, rifting, and the cycling of crustal material, setting the stage for complex life.

What is the Ediacaran Fauna?

The Ediacaran Fauna (635–541 Ma) includes some of the earliest multicellular, soft-bodied organisms. These creatures were mostly sessile and showed radial or bilateral symmetry, representing early steps toward animal life.

How are Banded Iron Formations (BIFs) connected to the oxygenation of Earth's atmosphere?

BIFs are layers of iron-rich rock that formed when oxygen produced by cyanobacteria reacted with dissolved iron in the oceans. Their formation declined once the atmosphere became oxygen-rich, marking the Great Oxygenation Event (~2.4 Ga).

What are the key pieces of evidence for global glaciation during the Proterozoic?

• Glacial dropstones: large rocks embedded in fine-grained marine sediments.

• Glacial till: unsorted debris left by glaciers.

• Cap carbonates: carbonate rocks that sharply overlie glacial deposits, indicating rapid warming after ice ages.

What are some hypotheses for how Snowball Earth formed?

• Reduction in greenhouse gases (e.g., CO₂).

• Continental configuration promoting weathering.

• Lower solar output during the Proterozoic.
  All could have reduced global temperatures enough to trigger runaway glaciation.

How does the glacier-albedo-temperature feedback loop explain Snowball Earth formation?

More ice increases Earth's albedo (reflectivity), which cools the planet further and leads to more ice formation. This positive feedback can drive Earth into a fully glaciated state—Snowball Earth.

How could a Snowball Earth event end using the concept of forcings and feedbacks?

While Earth is frozen, volcanic CO₂ continues to accumulate, increasing greenhouse forcing. Once high enough, it triggers rapid warming. Melting ice reduces albedo, reinforcing warming—a feedback loop that ends the glaciation.