The document provides a conversion multiplier to compare various timescales in geology, biology and human lifespan. It shows that 3.5 billion years ago the Earth formed without free oxygen in the atmosphere. Around 2.5 billion years ago, eukaryotic cells first evolved and oxygen began accumulating in the atmosphere. The Cambrian explosion of animal diversity occurred around 543 million years ago. Major extinction events occurred at the ends of the Permian and Cretaceous periods, wiping out many marine and land species. The first hominids evolved around 1.8 million years ago in the Quaternary period.