The end of the last Snowball Earth phase roughly coincides with the start of which period?

• A. Cambrian
• B. Ordovician
• C. Precambrian
• D. Permian

Answer: (A)

The question tests the timing of major climate events and their relation to the appearance of abundant animal life. The last widespread Snowball Earth glaciations occurred in the Neoproterozoic, and their end is followed by rapid warming and ecological diversification that marks the beginning of the Cambrian period. The Cambrian is when the fossil record shows a dramatic burst of multicellular life and hard-shelled animals, often called the Cambrian explosion. The Ordovician comes after the Cambrian, the Precambrian is the long interval before Cambrian, and the Permian is much later, so the end of Snowball Earth aligns with the start of the Cambrian.