The op is a few months old now, but the thread is still recent, so.. It's my conviction that the Bible doesn't clearly state how old the cosmos or our solar system, or our earth is., therefore the calculation of it being no more than 6,000 years solely based on adding up the years and ages of those that lived pre-flood, is an inaccurate method of dating the age of the earth. In view of the list of those mentioned are not for the purpose of telling us the earth's age. The direct genealogy only covers the line of Adam and his immediate descendants up to Noah., their names telling the gospel story. After that, if I'm not mistaken, the descendant list becomes indirect in it's lineage as it does concerning the genealogical list concerning Jesus.
And also in view of the few first verses in Genesis that indicate an unknown gap of time between a preadamic earth, the after effect of destruction resulting in a prenoaic flood and the earth being without form and void.. which happened before the arrival of any on the calculated 6,000 year list.
Such a catastrophic occurrence would I believe account in some cases for the million year dating, as well as the cases of samples being dated at much younger ages. I believe that the differences are due to the mixture of older soil, rock, bones with the younger soil, rock, bones during the two known of flood catastrophes,.. like clothing tossed in a dryer, none of the soil layers are strictly sequential.
Since God could have but didn't give any clear indication of the age of His creation, it is then considered a mystery that the various schools of education take upon themselves to search it out, if possible, or at least make an educated guess.
But I believe that specifics will remain unknown until we're in heaven, all sitting in our schoolrooms being taught by those who've gone before us and endeavor to catch us up... that is, if the knowledge has any significance to anyone of us there at that time. Personally, I'd be a most interested student in that heavenly classroom watching the provided educational movies of the actual events as they occurred. Either that, or the Eternal God will travel us back to that time so that we may observe for ourselves as the panoramic events unfold.