...some have looked at the sum of the numbers available in the Biblical genealogies and chronologies (about 6000 years)...

I don't think the biblical genealogies are the greatest thing for finding the age of the earth. They are there primarily to record the lineage of Jesus. However anything that differs drastically from them, such as the millions of years many people quote, is obviously incorrect.

The bristlecone pine tree named Methusaleh has been alive almost 4,800 years (and an even older one has been found). I doubt these trees would have managed to survive being under water for several months; they must have sprouted post-flood. Adding up the biblical genealogies puts the flood at about 4,400 years ago. This doesn't seem to be an outlandish difference to me, and would mean the earth is probably about 6,500 years old.

For bit more iffy of an estimate on the earth's age, try this: some scientists have been taking petrified bristlecone pine fragments and matching the outer rings with living trees’ inner rings. When the rings match for several years, they count the rings of the living tree back to the match, then use that to see how long ago the petrified tree was living, and count the rings back on the petrified tree to see how many years back it years it survived. They also match between know and unknown petrified samples to date the unknown one. They have matched and counted back to about 7,000 BC. Any takers on the idea of the earth being about 9,000 years old?