Others had tried to find an answer in geological processes—e.g.
Once the tree dies, it ceases to take in new carbon, and any C-14 present begins to decay.
The older a sample is, the less (the period of time after which half of a given sample will have decayed) is about 5,730 years, the oldest dates that can be reliably measured by this process date to around 50,000 years ago, although special preparation methods occasionally permit accurate analysis of older samples.
The idea behind radiocarbon dating is straightforward, but years of work were required to develop the technique to the point where accurate dates could be obtained.
What we breathe in is far from pure oxygen, but roughly by volume 78 per cent nitrogen, 21 per cent oxygen, 0.965 per cent argon and 0.04 per cent carbon dioxide (plus some helium, water and other gases).
The permanent gases in air we exhale are roughly 78 per cent nitrogen, 15 to 18 per cent oxygen (we retain only a small amount), 4 to 5 per cent carbon dioxide and 0.96 per cent argon, the CO2 being of course used by plants during photosynthesis. Matt Wormald, Neutral Bay Trees and plants give off carbon dioxide when they breathe, and when they die and rot.