So by measuring the C-14 level we work out how many half lives old the sample is and therefore how old it is.The trouble is that after 40,000 years there is under 1% of the original C-14 left, and it becomes too hard to measure it accurately.This isn't a fundamental limit as more accurate measurements could go further back, but at some point you'd simply run out of C-14 atoms.
Clearly, such huge time periods cannot be fitted into the Bible without compromising what the Bible says about the goodness of God and the origin of sin, death and suffering—the reason Jesus came into the world (See Six Days? He said, This only makes sense with a time-line beginning with the creation week thousands of years ago.
It makes no sense at all if man appeared at the end of billions of years.
Since 1947, scientists have reckoned the ages of many old objects by measuring the amounts of radioactive carbon they contain.
New research shows, however, that some estimates based on carbon may have erred by thousands of years.
For an example, when they tried to get the carbon dating for presence of Aboriginal people in Australia they get to the number 40,000. Why is that 40,000 years limit for carbon dating methods?
Carbon-14 makes up about 1 part per trillion of the carbon atoms around us, and this proportion remains roughly constant due to continual production of carbon-14 from cosmic rays.
Basically, it is correct to suggest 50,000–95,000 years.
The former is the practical limit (based on the calibration materials presently used in radiocarbon labs), while the latter is the theoretical limit of the AMS instrument.
But the radiocarbon detected in diamonds is equivalent to ages of up to 80,000 years.