You don't have to rely on carbon, there's the rubidium-strontium dating which relies on the decay of rubidium-87 to strontium-87. Rubidium-87 has a half-life of 50 million years (the amount of time for half its mass to decay into strontium). Using this together with other radioactivity decay dating methods is more reliable than just using one. It's like making sure you have a flashlight and candles in the house, in case of brownouts.
Because there are many of those uncovered--if there was only one, then I would doubt it myself. The more examples are uncovered, statistics would indicate that the probably of something being true will increase.
-RODION





