A slightly fringe nugget today. Here we go. Life originated underground. That's not the accepted view, but speak to anyone researching the question and there's a lot of hand-wringing about how simple organisms could get their start on the then hostile surface of our planet. There's also the problem that plants are at the base of most food-chains and yet photo-synthesising is not a beginner's trick. Gradually researchers have accepted that the earliest life used simple chemical reactions to power itself and not sunlight. And that it quite possibly lived in undersea vents where there's no sunlight, only very hot water and lots of dissolved chemicals - just like there is deep underground. Really, it's only a hop and a skip to accepting that early life began far below the surface where it's safe and warm, and conditions are stable. It evolved for millions of years until it got the hang of proper cell walls and reliable reproduction and all those other important functions. And as it got more resilient, it began to spread towards the hostile surface. Undersea vents were the halfway house until these ancient organisms had evolved sufficiently to colonise the oceans and the land. If you want to learn more, along with some extraordinary ideas about diamonds, oil, coal and earthquakes, then read the late Thomas Gold's book, The Deep Hot Biosphere.