In carbon 14 dating
Actually, that ratio may have been quite different.
For example, a worldwide flood would uproot and bury preflood forests.
The key questions then are: Has the atmospheric ratio of carbon-14 to carbon-12 changed in the past, and if so, why and how much?
They concluded that their findings are consistent with an Earth that is about 6,000 years old.
However, for the last 3,500 years, the increase in the ratio has been extremely slight.
Radiocarbon dating of vertical sequences of organic-rich layers at 714 locations worldwide has consistently shown a surprising result.
Cosmic radiation striking the upper atmosphere converts about 21 pounds of nitrogen each year into radiocarbon (carbon-14).
Most carbon-14 quickly combines with oxygen to form radioactive carbon dioxide, which then spreads throughout the atmosphere.