During Earth's history, it is believed that there have been several periods of extreme glaciation, known as "Snowball Earths." One such event occurred around 720 million years ago, during the Cryogenian Period. This event was so severe that it nearly wiped out all life on the planet. The entire Earth, from the poles to the equator, was covered in ice, blocking out sunlight and preventing photosynthesis. Life was confined to small oases in the deep oceans, where thermal vents provided warmth and nutrients. It is believed that the Snowball Earth ended when volcanic activity released greenhouse gases into the atmosphere, causing the ice to melt and life to re-emerge.
