The first part is right. It's the ratio that counts. But the C12 and C14 levels have been sampled at many depths in many places. Quite simply, there is NO consistant ratio in the ocean. Very deep places have CO2 that hasn't seen the atmosphere for millenia. The C14 ratio reflects this. Surface areas have a similar ratio to the atmosphere. Of course currents mix the two regions in unpredictable ways making it utterly impossible to use the ratios for dating.
So yes, a lot of CO2 comes from the atmosphere (though a lot also comes directly from fish and other sea creatures -- in fact more oxygen comes OUT of the ocean than diffuses in FROM the atmosphere). But it's not well mixed. There are places that have CO2 that have been sitting for millenia -- some of that water upwells in ocean currents and lowers the surface ratios in certain places. This effect is well documented. Going on about CO2 diffusing into the atmosphere is pretty pointless when that's never been debated.
It's really not that confusing. When there ARE meters of snow, the upper layers insulate the lower and daily temperature creates very obvious layers. I've noticed this every year in snow drifts around my house.
But when there is VERY little precipitation (hint -- these places are where ice cores come from) then the ice crystals on the surface have a very long time to form. Ice crystals form very differently depending on temperature, so there is an obvious yearly cycle. The yearly cycle also fluctuates as the Earth's overall climate changes.
Again, this has been calibrated in a number of ways. Ash from volcanic eruptions has been found in the layers corresponding to the date of significant volcanic eruptions. C14 dating has confirmed the dates of layers down to 100,000 years. Sunspot activity increases the presence of certain isotopes in 11-year cycles. This has been observed. There's at least a dozen other ways -- many of which were cited in the paper I linked to. I know reading isn't a whole lot of fun, but if you're interested in the truth, you might consider a bit of research rather than insisting that we break everything down into tiny chunks!
Of COURSE snails eat rock. In fact, most animals eat quite a bit of rock and dirt in their everyday diets -- it's only us humans that are so picky and won't eat off the ground.
Here's a paper with many citations that show exactly where the bicarbonate for the snail's shell comes from. This time, if you still don't believe it, why don't you look up the citations yourself -- it only takes a couple seconds in Google (or better -- scirus) and you can avoid wasting our time asking for sources we've already given you.
http://www.radiocarbon.org/Subscribers/Fulltext/v41n2_Goodfriend_149.html
I've worked with an instrument that measures the salinity of a solution to within a very precise range. Yet if I stick the leads of the instrument onto a dry salt crystal, it will give me wildly false results even though I KNOW the answer should be around 100%
You can always USE an instrument on specimines for which it's results are invalid. But if you ask a scientist about dating an arctic seal or a snail shell, they'll tell you up front that the date will be wrong. This is even stipulated in the submissions manual of every dating lab I've ever looked into.
Now if you don't follow their guidelines, they don't have ANY problem with taking your money and giving you their C14 reading. But to claim that the reading accurately gives a calibrated date would be a lie.
1. No there's not. In the scientific community we've got these wonderful devices called "microscopes." They let you magnify things so you can see even individual cells. Of course there are cases (like after a volcano -- like I mentioned before) where a tree does NOT grow for a few years due to damage. Using a wide range of specimines will account for this and even give you a better idea of when to EXPECT to have to look for a couple missing rings.
2. It's not arbitrary at all. You're matching PATTERNS, not just the 5th ring or the 10th. If they SHOULD be matched on the 5th ring, if you put it on the 10th the patterns won't match up. Sure, you may be able to match 5 rings out of 100, but it's obvious that you've done it wrong.
Draw 100 lines on a piece of paper with slightly different spacing. Then cut the paper into strips perpendicular to the lines. Finally, cut the strips into overlapping lengths and mix them up.
Sure, you'll probably be ABLE to connect them arbetrarily -- especially in cases where the strips just BARELY overlap so there's only one or two lines overlapping. But trees used for dating generally have DOZENS of overlapping rings in extremely distinct patterns.
When I was younger, my parents brought me to the science museum and we were lucky enough to get in on a professional talk about this sort of connecting overlapping tree rings. We were shown one slide in particular with five samples that overlapped -- it was so obvious MY brother could have done it (he was five at the time).
Later, I went to my grandparents house like I said and tried it for myself. Again, it was obvious to ME -- an amateur where the lines fit together. A professional would have many more techniques and MUCH more experience!
So no, it's not arbitrary, and yes, scientists make sure to use hundreds of samples from different sites to make the chronology.
As has been shown to you IN THIS THREAD as well as in at least two outside links, independantly published data from different CONTINENTS fit together perfectly.