Real life carbon dating
Archaeologists use the exponential, radioactive decay of carbon 14 to estimate the death dates of organic material.
It makes no sense at all if man appeared at the end of billions of years.
Carbon is naturally in all living organisms and is replenished in the tissues by eating other organisms or by breathing air that contains carbon.
At any particular time all living organisms have approximately the same ratio of carbon 12 to carbon 14 in their tissues.
So, we have a “clock” which starts ticking the moment something dies.
Obviously, this works only for things which were once living.