During 542–520 million years ago, which major event followed Snowball Earth?

• A. Cambrian Explosion
• B. The Great Oxygenation Event
• C. The Permian Extinction
• D. The formation of the Moon

Answer: (A)

The key idea is how major biological changes follow large-scale climate events. After the Snowball Earth episodes in the Cryogenian, the climate and oceans began to recover, creating new ecological opportunities. This sets the stage for the Cambrian Explosion, which occurs around 542–520 million years ago and is characterized by a sudden burst of life diversification and the appearance of many animal groups in the fossil record. The other events happened far outside this time window: the Great Oxygenation Event occurred about 2.4 billion years ago, the Moon formed around 4.5 billion years ago, and the Permian Extinction happened about 252 million years ago. Hence, the Cambrian Explosion is the event that follows Snowball Earth within this timeframe.