by Saman­tha Trumbo — Over 4.5 bil­lion years ago, the Earth was a su­per­heated sphere of molten rock, ra­di­at­ing heat to space at over 2000 K. A bil­lion years later, it had global oceans, teem­ing with mi­croor­gan­isms. In that time, the Earth un­der­went mas­sive ge­o­log­i­cal changes, some­how serendip­i­tously cre­at­ing con­di­tions right enough to lead...