Title: Globally-integrated spectral variability of the Archean Earth: The purple planet 

Abstract: The Earth has been inhabited for at least 3.8 Gyr and its appearance has changed with time. Here, we have modeled the 
Earth during the Archean eon, 3 Gyr ago. At that time, one of the more widespread life forms on the planet were the photosynthetic 
purple bacteria. We conclude that using photometric observations, it is possible to distinguish between an Archean and a present-
day Earth.