ion, but in time you s as muc apleasant feature in t sky.

    For a long time, astronomers assumed t toget tured t drifted by. e no about 4.5 billion years ago a Mars-sized object slammed into Eart enougerial to create t especially so as it ime ago. If it  ednesday clearly  be nearly so pleased about it. oour fourt crucial consideration:

    timing.tful place, and our existence is a s stretc played out in a particular manner at particular times—if, to take justone obvious instance, t been  by a meteor his in a burrow.

    e don’t really knoenceto, but it seems evident t if you ely advanced, ty,you need to be at t end of a very long ccomes involving reasonable periodsof stability interspersed  t amount of stress and cobe especially otal absence of real cataclysm. As o us, o find ourselves in t position.

    And on t note, let us nourn briefly to ts t made us.

    ty-turally occurring elements on Earty or so ted in labs, but some of tely put to one side—as, in fact,cs tend to do. Not a fetleknoatine, for instance, is practically unstudied. It able (next door to Marie Curie’s polonium), but almost not scientific indifference, but rarity. t isn’t mucatine out telusive element of all, o be francium,  is t tour entire planet may contain, at any given moment, fey francium atoms.

    Altoget ty of turally occurring elements are ral importance to life.

    As you mig, oxygen is our most abundant element, accounting for just under 50percent of t, but after t tive a