The exact moment where we can pinpoint the origin of complex life has long been a complicated question in itself. An even more recent discovery places the clock even further back at two billion years – with a different culprit responsible for the precise onset of complex life. When the Earth was formed 4.5 billion years ago, life existed as single-cellular units within two domains: bacteria and archaea. Somehow in the biological tree of life, there must have been an event that created these eukaryotes, and no one could pinpoint how they got there. With all theories on the origin of complex life comes skepticism. The quest for the origin of complex life on Earth brings up another enduring question: What about life outside of our planet?
The findings have led us to believe that these building blocks of life could have existed on Earth since its beginning.