4234
The older a sample is , the less there is to be detected , and because the half-life of ( the period of time after which half of a given sample will have decayed ) is about 5,730 years , the oldest dates that can be reliably measured by this process date to approximately 50,000 years ago , although special preparation methods occasionally permit accurate analysis of older samples .
 time: half-life
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 time: half-life