possible “snowball earth” (Marinoan) event, a terrible ice age in which the oceans froze all the way to the tropics. Life likely survived in limited oases such as the Caribbean, the Red Sea, the Persian Gulf, the Eastern Mediterranean, the Amazon, Central Africa, Indonesia, and Northern Australia. At the end of this latest Snowball Earth event, the oxygen concentration in the air suddenly increased from 1% to 20%, allowing the evolution of large, multicellular organisms.
