The lifeless earth was dominated by a handful of basic molecules: ammonia, methane, water, carbon dioxide, a smattering of amino acids, and other simple organic compounds.
Four billion years ago, carbon atoms mulled around the primordial soup. But as life began, those atoms did not spontaneously arrange themselves into complex life forms like sunflowers or squirrels. First, they had to form simpler structures like molecules, polymers, proteins, cells, primitive organisms and so forth. Each step along the way opened up possibilities for new combinations, expanding the realm of what was possible, until finally a carbon atom could reside in a sunflower.
