text: const MODERN_ACTIVITY= 15; 
  const HALF_LIFE_PERIOD= 5730;
  
  module.exports = function dateSample(sampleActivity) {
    
    if ( typeof sampleActivity !== 'string'
        || isNaN(parseFloat(sampleActivity) )
        || sampleActivity >= MODERN_ACTIVITY
        || sampleActivity <= 0 ) {
          
      return false;
  
    } else {
      let k = 0.693 / HALF_LIFE_PERIOD;
  
      return Math.ceil( Math.log( MODERN_ACTIVITY / parseFloat(sampleActivity) ) / k );
    };
  };
  