Life has found a home on Earth for around 4 billion years. That's a significant fraction of the universe's 13.77 billion-year history. Presumably, if life arose here, it could have appeared anywhere. And for sufficiently broad definitions of life, it might even be possible for life to have appeared mere seconds after the Big Bang. To explore the origins of life, first we have to define it. There are over 200 published definitions of the term, which shows just how difficult this concept is to gra