another tick of the universal clock saw these tiny grainsas always drawn to each other by that ubiquitous gravity we sometimes confuse with love , always eager to congregate , to coalescesettle together first into little clumps , then the little clumps into bigger clumps , then the bigger clumps into chunks , the chunks into bigger chunks , then rocks , then bigger rocks , then boulders and finally into bodies large enough to exert their own gravityboulders so large ( some eventually grew as large as 500 kilometers across ) that some of use have since named them : planetesimals .