we have had civilization on Earth for perhaps only a few thousand years.

 

Could you as a native speaker tell me what you understand from this sentence?

 

Could you please tell me the reason why "likely to be far older on average than ourselves."?

 

 

 

Source:http://www.ieltsg.com/search/label/reading%20practice%20test

1) Civilization appeared on earth a few thousand years ago, hence we have had civilization on earth for a few thousand years

 

2) The statement "Thus any other civilization that we hear from is likely to be far older on average than ourselves" is implied by the previous sentences which say: since the age of a planet is a several billion years then an alien civilization will be between zero and several billion years old. It's taking a probability based on there being more chance of finding a civilization in the range 'older than us' and 'younger than us'. 'older than us' would be between a few thousand and several billion years. 'younger than us' would be between zero and a few thousand. Since the older than us range is larger you would expect that age to be more likely.

 

Hope that helps and hasn't caused more confusion

Edited November 18, 201312 yr by pears

I'm closing this since you've already asked this question in your other thread.