Let's step back. 2 billion years back into Earth's evolution. A time full of life. But also mass extinction. An invisible killer was on the loose, ready to change the course of history. This was a time on Earth that directly impacted what the world is like today. The animals that inhabit it, the food you eat, and the air we breathe. Would you be able to survive in this new environment? And how did almost all life come to an end during this time?