The phrase "dark back of time" is often used to describe a period in history that is cloaked in mystery or difficult to understand. Synonyms for this phrase include "ancient past," "prehistoric era," "time immemorial," "distant past," "long ago," "forgotten time," and "bygone age." Each of these phrases conjures up a sense of time that is shrouded in mystery, distant from our current era, and difficult to comprehend. Whether it's the origins of humanity, the emergence of civilizations or the evolution of our planet, the "dark back of time" remains a fascinating and captivating subject of study.