1. Which era is the first that shows life on
   Earth?
   Cenozoic
   Archean

The Archean Era, which began around 4 billion years ago and lasted until about 2.5 billion years ago, is the first era that shows evidence of life on Earth. During this time, the planet was still forming its crust, and the atmosphere was mostly made up of methane and ammonia. The earliest known life forms were simple single-celled organisms, such as prokaryotes, which set the foundation for more complex life in later eras.

Fast forward a couple of billion years, and the Cenozoic Era, which began about 66 million years ago, is often referred to as the “Age of Mammals.” This era followed the mass extinction that ended the reign of the dinosaurs and allowed mammals to diversify and thrive. Today, we’re living in the Cenozoic and experiencing remarkable evolutionary changes right before our eyes!